Part Thirty Seven – A Long Tale About Water (And Life…..)

This thirty seventh entry was published originally by JSHarris on the 9th August 2015 and received 2,583 views on the closed forum


I know I’ve not been diligent in updating this blog, but it all comes down to one thing, WATER. The borehole saga is recorded elsewhere in the blog, but suffice to say that we have had massive ongoing water problems since, with many solutions being recommended and tried, most failing and many involving encounters with supposed experts who quite clearly were anything but. Anyway, this entry will be updated over the next week or so, as I hopefully work towards a solution that works. I’ve lost count of the number of variations on filtration etc we have tried, all failed to some degree; either in that they just didn’t work at all, or that they were too cumbersome, noisy etc to be a practical solution for us. Continue reading “Part Thirty Seven – A Long Tale About Water (And Life…..)”

Part Thirty Six – Winter Energy Consumption For Heating

This thirty sixth entry was published originally by JSHarris on the 29th December 2014 and received 1,188 views on the closed forum

Just a short entry this time to highlight energy use during this cold spell.

On Christmas Eve, at 15:00, I read the import and export meter readings, left the house heating on to maintain an internal room temperature of 20 deg C 24 hours a day, and went home for Christmas. I left the PV energy diverter on to keep the hot water system running, and the mid-point half way up the height of the thermal store was the same temperature when I got back today as it was when I left on Christmas Eve, 55 deg C.

I got back to the the house late this morning, around 11.45 am, and read both meters again. The import meter recorded that the house had used 29.8 kWh to maintain it at 20 deg C evey day, and the export meter showed that during the same time period the export meter showed that we’d exported 39.5 kWh from the PV system.

So, on average, the house used 7.7 kWh per day to heat, but generated 10.2 kWh per day. On the face of it, this looks like the house is (with no occupants and no DHW demand) actually generating more power from the PV system than it is using to maintain a room temperature of 20 deg C, 24 hours a day, during this cold spell (it was -5 deg C when I got to the house this morning). Continue reading “Part Thirty Six – Winter Energy Consumption For Heating”

Part Thirty Five – Hot Water And LEDs

This thirty fifth entry was published originally by JSHarris on the 13th December 2014 and received 2,255 views on the closed forum


I thought a bit more detail on the hot water system and some of the pitfalls of using LED lighting might be useful. I’ve added an instant water heater to the thermal store mixer valve output to allow for occasions when the thermal store temperature drops below that needed to deliver useful hot water. I’ve also found a few failings with using LED lighting that are worth sweeping up into one entry, in the hope that it may help others not make the same mistakes.

The hot water is provided by a combination of three energy sources now. The thermal store is pre-heated to around 35 to 40 deg C by the air source heat pump, whenever that is running in heating mode. It is then boosted up to around 70 deg C by the immersion heater, which is only driven by excess electricity from the photovoltaic panels. Whenever the panels are generating more power than the rest of the house is drawing, the excess is fed to the immersion heater. On bright days this will easily boost the thermal store up to temperature, but on cloudy winter days I’ve found that it often does little or nothing to increase the thermal store temperature at all. I only discovered this recently, with the onset of winter and the rapid drop in PV output. Continue reading “Part Thirty Five – Hot Water And LEDs”

Part Thirty Four – Things Are Going Slowly – And Some Hot Water Stuff

This thirty fourth entry was published originally by JSHarris on the 29th November 2014 and received 1,256 views on the closed forum


I seem to have been working hard on the internal side of the house for weeks now, but with little outwardly to show for it. At least all the flooring is completed, and the ground floor architrave and skirting is pretty much all done (except my study, which is still a store room), and most of the upstairs architrave is on. I am regretting opting for oiled oak internal joinery in some ways, as it’s taking a LOT longer to fit than plain old painted softwood. Looks OK, though.

We made a late change of plan and decided that, rather than have a fitted wardrobe along one eaves wall of the main bedroom (which would have hampered access to the service space in the eaves, via the small doors I’ve fitted) we’d have a walk-in wardrobe. Space was a bit tight, in terms of depth, because of the location of the bathroom door, but by making a thin partition wall I think I’ve managed to make it work OK. The wardrobe has ended up around 3.6m long by just over 1m wide internally, and this seems to be OK for loads of hanging space, plus shelves and drawers at the ends and enough room to get in sort of sideways at the hanging space. I’ve fitted another oak door and lining in the centre, so the right hand side is a “hers” space and the left hand side is a “his” space, with room access the “crawl door” into the under-eaves service area. Each side has 1.2m of clothes hanging rail, plus around 1.2m² of shelving/drawers, plus storage at floor level for shoes etc. It’s more wardrobe space than we currently use, I think, so should be OK. It’s taken a fair bit longer to think up a way of building it and actually getting the frame in and skinned than I thought it would, but has ended up being a lot more solid than I expected, even though the partition wall is only 52mm thick in total. Continue reading “Part Thirty Four – Things Are Going Slowly – And Some Hot Water Stuff”

Part Thirty Three – System Details And The Bathrooms

This thirty third entry was published originally by JSHarris on the 4th September 2014 and received 2,097 views on the closed forum


Following a few questions on the old Ebuild forum, and as I’ve had a serious re-think after some experience of the way the house behaves through a winter and most of a hot summer, I thought an update on the final system I’ve installed might be helpful. The most important observation is that heating is not an issue, in fact I very much doubt if the house will need any significant heating in winter, as it gets very warm just from the heat of the occupants. Working in it over December and January we found that tee shirts and open windows were needed by mid-morning and we never once needed any heat. In fact we had to stop using the 400W halogen work lights and replace them with low energy ones, as one of the halogens running overheated the house pretty quickly even in cold weather. Continue reading “Part Thirty Three – System Details And The Bathrooms”

Part Thirty Two – More On MVHR And Nasty Smells

This thirty second entry was published originally by JSHarris on the 21st July 2014 and received 2,047 views on the closed forum


Just a quick update, as I’ve not had too much time to work on the house over the past week or so, due to having had my car written off (and then having to spend hours on the phone sorting out all the paperwork etc).
One small problem we had, that I only found after I’d commissioned the MVHR system and done all the flow testing, was that there was no built in way to automatically switch the MVHR to boost mode when the bathrooms or kitchen are in use. The boost can be manually turned up, either by hitting the “party button” on the Optima controller, or by manually selecting a different fan speed, but I thought it’d be nice to have this done automatically. I looked at the Genvex wiring diagram, and it seemed there was an option for fitting a hygrostat, essentially a sensor that closes a pair of contacts when the humidity increases in the extract duct (as it does when using a shower, running a bath or cooking). A quick few phone calls revealed that these things were a silly price, and that even a really dumb, basically fixed point mechanical switch type unit was around £80. I really wanted something better than this, so was going to design and build one myself, when I came across a Polish company that sells some very neat little control and sensor units, including exactly what I needed to automatically control the Genvex MVHR. Continue reading “Part Thirty Two – More On MVHR And Nasty Smells”

Part Thirty One – It’s Slow Going On Your Own…………

This thirty first entry was published originally by JSHarris on the 6th July 2014 and received 1,212 views on the closed forum

Sorry for the delay in updating this blog. Lots has been happening but things are really grinding along slowly now that I’m working on my own on the fitting out. I’ve spent many days trying, and failing, to sort out the ongoing water quality problems from the borehole, interspersed with re-doing work I thought I’d completed because I wasn’t 100% happy with it. In between that I’ve been trying to complete the bathrooms and utility room fit out.

The ongoing borehole saga

Much of this has been related in later entries on a long running thread that was on the old Ebuild forum, but is attached here as a pdf file:    . In essence, it seems that our borehole is partly filled with sand and whenever the pump runs for any length of time it sucks sand up into the supply. I’ve played around fitting fancy filters, with centrifugal spinners to spin the sand out, but having tried two of these devices both clogged solid within a few minutes use. The main filtration system uses a combined pressurised sand bed and manganese dioxide media system, in a thing that looks like a giant scuba tank, with an electronic timer and control valve on top. The top of it can be seen in this photo – it’s around 1500mm high and 300mm in diameter, to give a sense of scale.


The timer/control valve box on the top of this unit switches a set of internal valves over to backwash the filter to a drain line every couple of days. It does this at 2 am in the morning, when there’s not likely to be any household water demand, although there is a 100 litre pressure vessel of clean water that can continue to supply the house during the backwash cycle. The fine sand in the filter traps sediment and the manganese dioxide oxidises the fairly high dissolved (ferrous) iron content of our water. This filter also has a compressed air space at the top, through which incoming water is sprayed. This aerates the water and drives out the small (but smelly) dissolved hydrogen sulphide content (think Bath spa water smell, for those who’ve been there). Pretty clear water from this filter then goes to a 5µ filter and activated carbon filter (the filters at the top left), then flows through a UV steriliser to kill any bugs, before flowing to the house. Inside the house there is a check valve, a 100 litre pressure vessel (that runs at 5 bar pressure) and a pressure reducing valve that regulates the house hot and cold water supply to 2.8 bar. There are also full bore valves at various points so critical bits of the system can be shut off, a bit like the stop c o c k on a mains supply, but a bit more complex because of the need to separately isolate pressure vessels full of water.

The problem I was getting with sand from the borehole was mainly during the filter backwash cycle. This flushes around 250 litres of water from the pump backwards through the sand filter, to blow any accumulated sediment up and out through the drain. It does this in 8 minutes, so demands around 30 litres a minute of water from the pump, at as high a pressure as possible. This is right at the maximum capacity of our borehole pump, so it is working pretty much flat out to deliver this flush water. Unfortunately, running at this rate causes it to suck up sand from the bottom of the borehole, clogging the pre-filter I put in place. After back flushing, the timer/valve unit on the filter activates a small venturi suction pump in the valve head that flows pump water to the drain and sucks all the water out of the filter pressure tank, leaving it full of air (the air is drawn in via the small grey tube with the white check valve and filter). It takes 15 minutes to do this, and uses around another 50 to 100 litres of water to create the suction. Once full of air the filter switches back to operational mode and fills with water from the pump, which compresses the air in it (as the inlet is at the top and the outlet is at the bottom) and leaves the compressed aeration pocket at the top.

Having found that trying to filter the pump water when it was running at 30 litres per minute or so during back wash was pretty much impossible, I decided to add a storage tank and second pump, primarily to deal with the high flow rate back wash flow requirement. In normal use the borehole pump will probably never need to deliver more than around 15 to 20 litres per minute, if that, so adding a relatively cheap tank and pump just to deal with the high flow rate seemed reasonable, and also gives the option of having another store of water, should we have a problem with the borehole pump at any time in the future. So, I now have a 650 litre tank in the water plant shed, fed via a solenoid valve and an aeration venturi (it made sense to fit this, as pre-aerating the water used for back flushing stops it from reducing the oxidising capability of the filter media). This 650 litre tank has a float valve that turns the solenoid valve off when it’s full. The tank is re-filled at a relatively slow rate from the borehole pump (flow rate is limited by the 6mm orifice in the venturi aerator). A second pressure pump draws water from around 3/4s of the depth of this tank and feeds (via a check valve) the supply to the filter. This pump set is controlled by a second pressure switch and a time switch, so that it only operates when the filter is going to backwash, normally (although over-riding the time switch would allow this pump to feed the house if needed). Thankfully the extra tank and pressure pump set wasn’t that expensive. The tank was around £220 and the pump another £120.

I have the borehole drilling company coming out to air lift the accumulated sand in the borehole, too, and am going to replace the borehole pump higher than it was, in the hope that it will stay clear of any sand that runs back into the hole via the 0.5mm wide slots in the bottom 12m section of the borehole liner. At the moment, the whole of this slotted section of liner is packed hard with sand, so all the water the pump is drawing is being sucked up through the sand, which is one reason why, at high flow rates, the sand gets disturbed and pulled upwards into the pump. Fingers crossed that I may get a reliable water supply within the next couple of weeks. Thankfully there is no shortage of water, the borehole can easily sustain pumping at 2000 litres per hour for days on end, non-stop, and I doubt we’ll ever use more than around 500 to 600 litres in a whole day, and then only when the filtration system backwashes.

Fixing things that should have been done properly the first time

Like most blokes, I suspect, I’m not good at reading instructions before I launch in to doing things. Although the ASHP install went well (around 1/2 day) and it worked as expected (once I’d fathomed out all the missing information from the manufacturer on what the controls really did) it did create some noise inside the house when it was running. This was really odd, as it was almost completely silent outside, yet inside the house there was a distinct hum in the utility room whenever it was running. Not really loud, but enough to be annoying. After reading through the installation instructions (properly….) I realised that my attempt at reducing heat losses might be to blame. The manual makes it clear that the flow and return pipes should be connected to the rigid pipes coming from the house using 1m long full bore flexible hoses. I had thought this was OTT, as it would have meant having long loops of hose outside, so I hooked it up using 300mm full bore flexible hoses, and wrapped these with insulation. It turns out that the long flexible hoses are needed to isolate the compressor vibration from the house structure. Here’s a photo of the short hose I originally used (after I’d removed it) and another photo showing the new long hoses (before I fitted armorflex insulation over them:


The difference doing this has made is staggering. The ASHP is now inaudible inside the house, the only way to see whether or not it’s running is to check the display. Clearly the short pipes I’d used were conducting vibration into the rigid pipework and hence into the house, whereas the longer pipes stop this completely. Had a read the instructions properly I’d have realised this, and could have saved a couple of hours work in draining (and saving) the antifreeze, replacing the pipes and refilling the system.

The second re-work was very similar, and relates to noise and me not following the manufacturers instructions for the MVHR. Although the MVHR is virtually silent most of the time, whenever it goes to active cooling mode there is some noise, mainly from the extract ducts. To be fair, the installation manual makes it clear that duct silencers should be fitted to the big ducts close to the MVHR unit, but because I changed my mind and only decided to fit this big Genvex unit after the house was designed, I ended up with insufficient space to fit silencers. I also had to re-jig the service area layout to fit the big Genvex unit, and this also reduced the space available for silencers. After a bit of head scratching, and researching how duct silencers work, it seemed easy enough to make some custom shaped ones. Essentially they are just absorption silencers, that are lined with a layer of sound absorbing material. They aren’t very high tech, all that’s needed is a big enough volume to allow the air through without restriction, plus some sound absorbing foam.

The fresh air supply silencer was easy, as it could just be a big rectangular box that fitted on top of the supply manifold chamber, with a central baffle and a couple of duct fittings. Unfortunately it’s impossible to photograph, as it’s sat down in the narrow eaves space behind the MVHR unit. The extract silencer was more of a challenge, as the only space I had to fit it was up against the underside of the roof service space battens.Here are some photos, first the front view:

The extract manifold is the thing with all the blue ducts to the left, the bit of left over green vapourblock board forms the front of the silencer. The just visible short sliver flexible duct goes to the MVHR extract intake.

Here’s a side view of the silencer, which gives an idea of the shape and size.

Finally, this is view of the acoustic foam lining:

These silencers have made a very big difference to the sound level indeed. Even on full boost cooling the MVHR is virtually inaudible in the bedrooms and living room, and can only just be heard in the utility room (which is right underneath the service area). If I’d had the space I’d have perhaps made them a bit bigger, as they are so effective at reducing noise that I think it should be possible to make the MVHR virtually inaudible everywhere in the house, even at full boost when cooling or heating the house.

The foam I used is fire-resistant acoustic foam used for insulating studios and the like. It wasn’t that expensive, as I bought some big sheets to line the walls of the service room, and just used offcuts for the silencers.

Finally, for anyone looking to use the same Genvex MVHR unit, I can offer another tip to same money. This unit has the option to add humidity sensing to the extract duct, so that if it senses increased humidity (such as when a shower is running, or perhaps from cooking) then the MVHR will automatically go into boost mode, to increase the extract and fresh air supply rate. There are no-volt contacts on the MVHR to switch the unit to boost, so what’s needed is a humidistat, placed in the duct so that it closes a pair of contacts when the humidity exceeds a set point. Standard duct mechanical humidistats are both expensive (well over £100) and fairly crude, with poor adjustment of the true relative humidity switching point (because they are also very temperature sensitive) and no control at all over the hysteresis (the relative humidity difference between the switch on and switch off points).

After a bit of digging around I found a Polish manufacturer that makes a very neat little unit (…latory/dhc-100/ ) that can be programmed both for set point and hysteresis, plus has some added features like time delay switching (so you can set an over run time if you wish). Best of all is that this unit is 100% compatible with the Genvex (it has no-volt relay contacts, and will run from the 24V supplementary valve power supply that the Genvex has) and only cost £43 delivered. It also has a nice RH display, and is accurate to 0.5%, so should be a handy way of monitoring the extract humidity level to get the right set point for switching the MVHR to boost.

I’m cracking on with finishing the second bathroom this week, then will start the main bathroom, after which I can have a good clean up and start fitting the bamboo flooring on the first floor. I will be glad to finish with doing plumbing, especially all the stuff to do with the bloody borehole………………


joiner 06 Jul 2014 03:04 PM:

 With so many female contributors on here now, this is not the time to go reinforcing the “men don’t read instructions” illusion that women are so fond of insisting has more than just a grain of truth in it!


 jsharris 06 Jul 2014 03:25 PM:

 The problem is that for both of the above cases it is, unfortunately, true! In the case of the ASHP install I thought the requirement for 1m long flexible hoses in the instructions was daft, as it would cause additional energy loss from the hot/cold pipes to the outside air in winter/summer. I didn’t realise until reading the instructions more carefully that the real reason for needing long flexible pipes was to get rid of the noise transmission path.

 A quick wander around our build will find quite a few unopened plastic bags with instructions inside, I’m afraid……………


 ProDave 06 Jul 2014 03:38 PM:

 the trouble with men is they don’t just need to be told HOW to do something, but we need to know WHY. If we are not told why, then we do it our own way.


 joiner 06 Jul 2014 04:22 PM:

 I know, but no need to go advertising it!

 Thank god the wife doesn’t read this stuff or my life would be misery.


 jsharris 06 Jul 2014 04:50 PM:

 Spot on Dave (ProDave). The mistake with the ASHP pipes was me thinking I knew better than the manufacturers, and that shorter pipes would always be a good thing, not realising that they knew that noise transmission was a problem unless you use longer pipes.


 SteamyTea 07 Jul 2014 08:36 AM :

 What are these instructions in plastic bags you talk of. I have never seen them.

 I made a Temp/RH logger with some DHT11 sensors, these are cheap, made for A/C units, but do seem to require airflow to get an accurate reading.


 Calvinmiddle 08 Jul 2014 04:19 PM:


 I know you used the HB+ ducting but looking at the manifolds that you used it looks like you used the flat 400 x 400.

 I’ve been looking ta the CVC website and there is another manifold that looks like it also might act as like a silencer as there is a much bigger air volume in them.

 Did you notice these? Or have I got it wrong and they aren’t mean to act as a silencer.



jsharris 08 Jul 2014 05:06 PM:


Yes, I did look at these, but they were too big to fit in the limited space I had, which is why I went for the smaller manifolds. I think that these bigger manifolds might silence a bit, but they don’t have any acoustic lining to absorb sound, so could only really work as expansion box silencers. My feeling is that this would be fine for airflow noise, but probably not for the transmitted noise from the motors in the MVHR unit we have. The big advantage of those bigger manifolds is that it is a lot easier to gain access internally, which would be a big help when balancing the system. Balancing is done by inserting annular rings of differing diameters into the manifold duct fittings, and needs access to the inside of the manifold to undo the quarter turn locking ring on each incoming duct, insert the ring, replace the locking ring, refit the 150mm duct, then go back around the house checking all the terminal fittings to see how the change has affected the flow rates. This is a bit of a tedious and iterative process, and gaining access into the smaller manifold is tight and has to be done by feel through the 150mm duct hole, making the process even harder than it need be.


 PeterStarck 10 Dec 2015 07:07 PM:

 As a new member I’ve been working my way through this excellent blog. I can fully relate to the various problems of all types you have encountered during your build. For instance my 47m deep borehole started off as a deepbore soakaway, but that’s another story. I will be installing a Genvex Combi 185 and I was told by the suppliers that controlling it with humidistats wasn’t a good idea because of their unreliability. I’m therefore very interested in the Polish humidity controller you mentioned. I found a similar looking one on Ebay but from the price suspect that the sensors are not as good as your one. Have you looked at the one linked to below, my Polish is nonexistant and comparing them is difficult. The dimensions are not quite the same even though they look similar.…sd=191324730505


 jsharris 10 Dec 2015 09:06 PM:

 Hi Peter,

 Glad you’ve enjoyed the story so far.

 I’m not sure about the Chinese units; I went for the Polish unit for two reasons. The first is that I’ve not been wholly impressed with some Chinese made equipment, the second is that I worked for a while in Southern Poland and was very impressed with their work ethic and attention to detail.

 I have a copy of the English instructions for the Polish humidistat, and have to say that so far it has worked flawlessly. The only slight problem is that I need to change the the threshold twice a year, as the warmer months tend to be dryer, so it’s better to have boost come on at around 60 %, in the late autumn and winter the threshold needs to be increased to about 65% to allow for normal seasonal changes.

 I suspect that much of the unreliability that is reported is down to poor quality sensors plus a failure to recognise the seasonal humidity changes.

 I’m impressed with the Genvex Premium 1L we fitted. It works very well, has a LOT of programming options via the Optima controller (the same one used of the Genvex 185 I think). It takes a bit of wading through the manual to get to grips with all the settings, though.

 BTW, buying a Genvex from Denmark is massively cheaper than buying from the only UK distributor, Total Home Environment. I bought our unit from, saved around £3000 and can get back the 25% Danish VAT. Their service was good and they knew more about the product than the UK dealer.


 PeterStarck 11 Dec 2015 08:04 AM :

 Hi Jeremy, thanks for your help.

 Based on what you’ve said I’ll be buying the Polish humidistat.

 I went to Total Home Enviroment to look at the Combi 185 a couple of years ago and they were very helpful. The only problem is they ring me every few months now asking me when I will be buying the unit. I searched for Danish suppliers but never saw so thanks for that. I shall look into it.


 jsharris 11 Dec 2015 09:19 AM :

 We also went to Total Home Environment and had a quote from them for both supply only and supply and install. The supply only quote from THE for just the Genvex Premium 1L active MVHR was around £8,200 inc VAT, plus around £2,200 for ducting (inc VAT) and another £3,000 (again inc VAT) for installation labour, making the total around £13,400.

The price from Sundthus for supply and delivery of exactly the same unit was £5,200, including Danish VAT at 25% (which can be reclaimed from HMRC I found).

So, comparing just the unit price, after recovering the VAT, THE wanted about £6,830 to supply and deliver the same unit (with the same warranty) that Sundthus would supply and deliver for £4,160. Sundthus were great to deal with, spoke and wrote excellent English and now even list a UK delivery price on their web site (I was, I think, one of their first UK customers and they had to get a price specially for me).

The unit they supplied came with the English manual and was pre-programmed in English, so was no different to the one that would have been supplied by THE. I’ve just checked, and currently Sundthus have the Combi 185 L-S for 42,772 Danish Kronor (including Danish VAT at 25%), which at today’s exchange rate is about £4,134 (inc 25% Danish VAT) and UK freight charges of 1550 Danish Kronor which is around £150 (again inc Danish VAT at 25%).

Worth comparing those prices with those you get from THE – I’ll lay money that they are a lot keener!


PeterStarck 11 Dec 2015 12:34 PM:

I looked at the Sundthus site this morning and the prices are certainly much lower. I put the site through Google Translate and I think the DKK42772 price is without the VAT and with VAT it is DKK53465. It is still a large saving on the UK price though. It’s also interesting about the delivery.

What is the situation regarding the guarantee when buying from Denmark?



Part Thirty – MVHR Details

This thirtieth entry was published originally by JSHarris on the 29th April 2014 and received 2,012 views on the closed forum

Just a short update with some details of the MVHR install, and a brief explanation of how I drilled some big holes through the airtight walls of the house………………….

One job I’ve been putting off was cutting the fresh air inlet and exhaust air outlet duct holes through the walls of the house. Ideally I’d have put these in before the insulation was pumped in, but at that stage I hadn’t purchased the MVHR and so wasn’t quite sure where I wanted the holes.

The technique I used was this. First I made up a 600mm long 6mm diameter drill, by drilling a 3mm hole in the end of a bit of 6mm bar in the lathe, turning down the shank of a 6mm wood drill bit to 3mm and then silver soldering the two together. This very long drill allowed me to accurately drill a pilot hole through the wall, in a location free from any internal timbers. The secret to getting it to go straight was to get a block of 70mm square timber and drill a 6mm hole through it that was square on one axis and had a 1 deg angle on the other axis. Holding this block against the inside of the wall and using it as a drill guide ensured I got the long drill through square, with a slight downward angle to ensure no moisture could ever run back into the house via the duct. Once drilled right through I undid the drill chuck and left the drill in the hole as a guide.

Next I used a short bit of batten with a 6mm hole in one end and another hole in the other end the right size for a pencil. I spaced these holes about 80mm apart, so that when I slipped the 6mm hole over the drill I could draw a 160mm diameter circle on both the inner and outer walls (the latter from the top of a ladder). Next it was out with the jig saw to cut the wall skins out (fiddly for the one shown below because it’s the fresh air intake and is right in the corner of the eaves).

In the photo above you can see that the inner airtight/vapour block skin has been cut away and the warmcell insulation (the grey stuff) is packed solidly in the cavity, even in this corner at the very top of the wall and around a metre or so from the nearest injection point.

Next, a plastic funnel was taped over the end of a bit of 150mm PVC duct (pointy end out, and the nozzle taped over) and the whole thing pushed through the wall from the outside (only so that any displaced warmcell fell inside). The cone of the funnel tended to compress and displace the warmcell as the duct slid in, ensuring that very little is lost and that it is packed tightly around the duct. Before pushing the duct right in, I fitted the external terminal to the duct and squirted expanding foam around it before pushing it right home, to seal up around the duct exit in the outer skin. I then pushed the thing home and screwed the terminals to the cladding, then fitted the grills to them. They are dark brown and blend in reasonably well with the larch.

To seal the inside, which is far more critical, I first used low expansion foam (the pink stuff) to fill around the duct and bond it to the inner skin. Before the foam cured I wiped around it with a gloved finger to get a fairly smooth inner surface. As a belt and braces seal, I then added Siga airtightness tape to seal all around the joint. The photo below is the exhaust duct, but shows the same sort of seal (the exhaust duct is easier to photograph, as it’s higher up on the gable wall, rather than very low down on the rear wall behind the MVHR unit).

Having got these ducts fitted, I could then shift the MVHR unit (all 78kg of it…….) on to the mount I’d made for it. I’m keen to minimise noise that may be transmitted from this unit to the house structure, so as well as using very short lengths of flexible duct to connect it up as vibration isolators, I also used four rubber anti-vibration mounts to support a base frame that the thing sits on. This raised the MVHR up (which makes it easier to service and allows room underneath for the condensate drains). Here’s a photo of one of the rubber bobbins I used (the keen eyed will recognise these as Mini exhaust mounting bobbins……….):

I’ve kept all the duct runs from the MVHR to both the outside fresh air/exhaust terminals, and the house extract and supply manifolds, as short as I can to reduce losses. The system uses radial ducting (the Swiss HB+ sytem) so every vent in the house comes back to a common manifold. This is the extract manifold, fitted to the wall to the left of the MVHR:

And (tucked away in the tight space on the floor behind the MVHR) this is the fresh air feed manifold:

Finally, this is a view of the installed MVHR with all the ducting connected up, showing the house feed and extract end:

And another one showing the fresh air feed and exhaust end (the fresh air feed is behind the MVHR box down at floor level, on the rear wall):

The next job is to finish the wiring (pretty simple, just power and a four way control cable that goes to the controller already fitted down in the hall), add some insulation around the fresh air inlet and exhaust ducts and then test and commission the unit. I suspect that adjusting flow rates may be the most tedious bit, as this has to be done by measuring the flow at each extract and fresh air feed terminal (using a low air speed measurement unit) and then adjusting the flow rate by swapping restrictor plates over in the fittings where each radial duct fits to the manifold.

Hopefully the above may be of use to anyone else contemplating their own MVHR install. So far it’s taken me about a day to fit all the first fix ducting and perhaps 3/4 of a day to fit the unit itself and connect up all the ducts. In addition to doing this today I filled the primary ASHP circuit and leak tested it (hence the damp patch on the floor under the small PV for this circuit) and tested the ASHP briefly (seems to work, but I need to read the manual tonight to programme it).

I’ve edited this post to add a photo of the intake and exhaust ducts, taken from the North East corner of the plot. The exhaust is on the left (on the East gable wall) and the intake is on the North wall, right under the eaves.


ProDave 29 Apr 2014 06:47 PM:

 Great information as always.

 One question abut drilling the holes through the outer wall:

 Did you cut the outer skin in one go with the timber cladding in place? (long jig saw blade to cut both the cladding and outer skin of the wall together)

 Or did you remove a section of the timber cladding, Drill the inner and outer skins of the wall, then drill the cladding to match and replace?


 jsharris 29 Apr 2014 07:15 PM:

 I did it in two stages, Dave, but had I had a longer jigsaw blade I’d have done it in one go. I ended up using the jigsaw to cut through the cladding, then fiddling around with a Bosch multitool to cut out the outer OSB skin (pretty fiddly when doing this up a ladder).

 The outer terminal covers I used (these ones: http://cart.vacuumsd…d=377&parent=46 ) had a surround that’s a fair bit bigger than the duct, making it easy to have a bigger hole in the outer skin and use squirty foam to seal it up.


 couplands 01 May 2014 05:53 PM:

 Just wondering if you have to worry about the build-up of static in the ventilation system. Ive seen with air extraction systems in workshops (albeit at higher flow rates), that the plastic pipes need to be grounded using copper wire along their length.




 jsharris 01 May 2014 07:07 PM:

 Not as far as I’m aware. Lots of MVHR systems use plastic ducting and none use any form of conductive coating or wire, as far as I know.

 I fired up the MVHR unit today and it seems to work OK, nice and quiet when in passive mode at low fan speeds, but there is some noise when it’s in active mode. This worried me at first, as when I turned it on it defaulted to active heating, with the fresh air feed running at around 40 deg C, the exhaust at around 4 deg C and a fair bit of noise coming down the ducts. An added problem was that all the menus were in Danish (because I bought the unit direct from Denmark) so it took me a while to work out how to switch it to English and turn the temperature down so it wasn’t in heating mode.

 In passive mode and with the fan speed at the lowest setting it’s pretty much inaudible in the bedrooms and living room, but can be heard in the utility room and downstairs WC. I didn’t fit silencers to the fresh air feed and extract ducts, before the manifolds, but I’m sure it does really need them (the manual says they must be fitted). I’m now going to make up some silencers and fit them tomorrow, should be easy enough, just some big expansion boxes with some acoustic lining.

 The really good news is that the vibration isolation seems to work very well indeed, the only noise I’m getting is through the ducts. One advantage of a sealed and well insulated passive house is that it is very, very quiet inside with the doors and windows closed, although this does mean that any installed system has to run quietly.


 SteamyTea 11 May 2014 10:18 AM :

 When it comes to commissioning and balancing the system, how do you cope with the permutations of doors in the house being open or closed. Some doors you know are usually closed (bathroom, toilet (or is it lavatory, I never know), utility room. But other doors can be left open, or closed, depending on mood.


 jsharris 11 May 2014 10:55 AM :

 For the purposes of the report for building control I just left all the doors open, as that reduced the variation I was getting from the wind outside (wind is a real problem – I was seeing about +/- 30% flow variations second by second on pretty much every terminal on a very slightly windy day).

 There are three things to do when commissioning the system, I think, plus the final tuning after you’ve done the building regs tests.

 The first is to balance the fresh air feed in and the exhaust out, by restricting all the ducts (at the manifold end) for the higher flow side (in my case the sum of the extracts started off around 40% more than the sum of the fresh air inlets).

 Next is to set the MVHR to it’s highest speed (in our case fan speed 4) and check the extract flow rates against building regs (6l/S in a WC, 8/lS in a bathroom or utility room, 13 l/S in the kitchen). This needs a bit more balancing, and may involve opening up some extracts (like the kitchen) and closing down others (like the bathroom, WC and utility), double checking that the sum of the flow from all the extracts after doing this is the same as it was before.

 Next you set the MVHR to it’s manufacturer recommended occupied house running speed (in our case that’s fan speed 2) and measure the total flow out of, and into, the house to ensure it exceeds the building regs minimum continuous ventilation rate. For us this gave a flow rate that was a fair bit higher than building regs needed. Our habitable floor area is a bit under 130m², so using the building regs minimum of 0.3 l/S per m², we needed about 39 l/S. I found that I was getting over 50 l/S on fan speed 2, so switched the unit down to fan speed 1 (the unoccupied house level) and found I still got more than 40 l/S total, with no noise at all in most of the rooms.

 That completed the building regs compliance bit, so I then went around and shut the WC, bathroom, bedroom and kitchen doors and checked the flow rates again. On the lowest setting they didn’t noticeably change, but on fan speed 4 the extract rate in the kitchen, utility and WC dropped a fair bit. This is because the only source of air into those three rooms is via the 8mm gap under the kitchen door (which was howling a bit when I did this). Opening the kitchen door got the flow rates pretty much back to where they should be, and reduced the noise a fair bit.

 In practice the flow rates will vary a lot from whatever they’ve been set at during the building regs compliance testing, as differential wind effects on the external exhaust/intake terminals seems to have a big impact. In my case this impact is made worse as I have the exhaust on the East facing gable and the intake on the North facing wall, right under the eaves (I’ve just edited the post above to show the arrangement of these terminals on the outside). I’m bound to get fairly wide variations of dynamic pressure from the wind between these two locations, so a fair bit of variation is to be expected. I’d imagine that situations like this must cause problems when doing measurements in a lot of installations, as, in terms of avoiding cross flow from the intake and exhaust, it makes sense to position the exhaust on the wall opposite the prevailing wind and the intake as far away from it as possible.


 SteamyTea 11 May 2014 05:47 PM:

 Now I am lodger free again I can use the prevailing wind to ventilate my place again. Suppose it is worth checking again when wind is in different direction, just for fun mind.

Good that you are compliant at the lowest, and quietest, setting.


 Calvinmiddle 21 May 2014 11:27 AM :


 Has your BCO come back yet saying he is happy with the method you used to commission your system?


 jsharris 21 May 2014 08:43 PM:

 I’ve not heard a thing from the BCO, which usually means that he’s OK about things. If there was a problem I suspect he’d have let me know by now, as in the past he’s been pretty quick at getting back to me with anything that wasn’t clear.

 I won’t seem him again for a while, as our next inspection is the final completion one, which won’t be for a while yet as I’m now doing everything else on the house myself, which is turning out to be a slow job!


 coopers 25 May 2014 07:21 PM:

 Hi Jeremy, Did you implement the “poo-smell-direct-ducting” that we were discussing a while back?


 jsharris 26 May 2014 02:45 PM:

 Yes, I’ve put the ducting in and looked inside the plastic built-in cisterns we’re using to make sure there is a direct air path out from the flush pipe. The answer is that I was right, there is a good direct connection from the airspace above the water in the cistern to the flush pipe, so there’s no reason in theory that this system shouldn’t work.

 Whether it does or not depends on whether there’s enough airflow to overcome the tendency for smells to disperse. The biggest connection I can practically make to the cistern is with a 32mm flange fitting, but I’ve run 40mm pipe along the eaves space from the extract manifold, and that does seem to have a fair bit of “suck” at the end, especially when the MVHR is in boost mode. The biggest restriction is inside the cistern, the internal overflow pipe that connects the air space to the flush pipe is only about 20mm, so will only allow a limited flow rate. I suspect that the flow rate needed is probably pretty low, though, you don’t really want a massive draft down there!


 Calvinmiddle 27 May 2014 03:05 PM:

 Have you more details of this “poo-smell-direct-ducting” as it is something that interests me. I have seen this product advertised, is it this or something like this?

 I find the search function on the site hard to use and can’t really find anything


 coopers 27 May 2014 07:31 PM:…_+odour +buster


 Calvinmiddle 29 May 2014 12:03 PM:

 Thanks Coopers

 Jeremy – if I understand this you are running the extraction from the pan (via the cistern) all the time. Is there a 40mm pipe conected to the manifold directly for each of the 3 toilets – so each pipe is acting like the extract from another room in a radial system (abet with a 40mm pipe reducing to 32mm) Or does the 40mm pipe split and and serve all 3 toilets.


 jsharris 29 May 2014 05:46 PM:

 Unfortunately it’s impractical to fit this to the downstairs WC, as I only had the idea after the boxed in and insulated soil pipe stack had been plasterboarded and plastered, so I’ve no easy way of getting an extract duct down there now. For the bathroom WCs, what I’ve done is make a home-made adapter to connect a 40mm waste pipe to the extract manifold. This 40mm pipe runs along the top of the eaves service space, and both bathrooms have their WCs fitted against this stud wall. I’ve fitted a swept tee off the pipe to the first WC and a bend to the second WC, with both reducing down to 32mm flange fittings on the cisterns.

 Yes, the extract is continuous, but at a pretty low rate. I have a feeling that the air flow rate needed to disperse odours down and out only needs to be pretty low, just enough to counter natural dispersion that would occur otherwise. The system will undoubtedly work better (assuming it does actually work at all) if the toilet lid is closed quickly after use, something that will, at least, please the female member of the household……………….


 Calvinmiddle 01 Jun 2014 12:10 PM:

 Thanks Jeremy

 I’m finding this interesting as due to the limitations of the plot we only have clerestory windows in the bathroom and its three metres to the bottom of them. My wife is insisting that the windows need to open but I’m telling her there is no way to reach them and the MHRV to get rid of odours in the bathroom – also showed her the odour buster video showing smoke getting sucked down as this makes sense as opposed to dragging the smell across the room to the extract vent.

 She is from Australia so airtight houses with closed windows is something of an alien concept as windows are there to let breeze in to cool the house in her eyes.


 jsharris 01 Jun 2014 01:17 PM:

 I can empathise with overcoming the “we must have windows that open” problem! Not only is my other half convinced that opening windows is “healthy” it was also a recurring theme from questions asked during our open weekend.

 The idea of drawing odours directly from the toilet pan seems obvious, to me, and makes me wonder why on earth we didn’t think of doing it years ago. Apparently the odour buster units have been marketed in Malaysia for years and the story I heard was that they were invented there to overcome this problem in a relatively sealed house that relied on air conditioning to keep the temperature and humidity within reasonable limits.

 I’m just hoping that the MVHR will have enough oomph to do the job, but I do have a fall back option if it doesn’t, and that’s to get a couple of the cheap ebay fan units, discard the charcoal canister and connect them to the MVHR extract ducting as booster fans.


 vk2003 16 Aug 2014 04:31 PM:

 The only thing I would worry about with connecting your mvhr to the toilet pans, is the bacterial aerosol load that will get drawn up into your system/manifold. Have you put an inline filter in to prevent this?


 jsharris 16 Aug 2014 05:40 PM:

 I’ve answered this question here:…dea/#entry95090 , as best I can, but I don’t think it will present a problem at all, as other systems are sold that do pretty much the same thing, like this unit: and they include an activated charcoal cartridge, which would be a breeding ground for aerobic bacteria. Luckily, faecal coliform bacteria are anaerobic, so won’t survive for long in a dry, aerobic environment like an air duct.


 iSelfBuild 13 Mar 2015 06:02 PM:

 Just nearly had a heart attack when I saw how much your MHVR unit was in your cost breakdown… but it doubles as your ASHP! Very interesting.


Part Twenty Nine – Some Details That May Be Of Interest

This twenty ninth entry was published originally by JSHarris on the 23rd April 2014 and received 2,303 views on the closed forum

I’ve been asked a few questions about technical details and costings, so thought it might be useful if I added a bit of detail.

First of all, how much has it all cost?

Our site costs were high, and not very typical of most sites, so what I’ve done is break down the other costs and add in the basic ground works cost, just for the house alone (excluding the garage), to give an idea of how the costs break down. Bear in mind when looking at this that there is a fair bit of DIY in there; I was the architect, project manager, first and second fix plumber, ventilation and heating system installer and have done a fair bit of other stuff.

Simplified costing spreadsheet – 050421014

So far the total looks like it’s going to come out at around £173k just for the house and basic landscaping. This seems reasonable for a house that comfortably exceeds passive house performance levels and is reasonable well finished internally (we could have saved a fair bit by not opting for oak doors, staircase and joinery, and going for a cheaper spec for the kitchen and bathrooms). Hopefully this might be of use to others.

Next I thought I’d add some details of the technical stuff. Dave (ProDave) asked how I’d fitted everything into one meter box, so here’s a photo:

It’s a tight squeeze, but everything fitted in there (just). The lower box is a modified caravan hook up box, that I used as a temporary site supply initially, but is now permanent. It has four RCBOs, one feeds the blue 16A socket, one feeds the treatment plant the third feeds the borehole water pump and the fourth feeds the garage, which is TT’d locally, rather have the earth exported out over the SWA. The two way CU in the lower right corner just  feeds the waterproof CU below, as an isolator. The 80A fused isolator in the top right corner feeds the 25mm² SWA that runs in a duct under the slab and up to the services area in the “loft”. The garage has its own RCD protected two way CU, one circuit for lights, the other a ring main running a lot of metal clad sockets all around the walls, but the earth for this is TT’d, just for my peace of mind.  The 6mm two core SWA that feeds it is fed by a 40A DP RCBO, so the underground cable is well protected, too.

The 25mm² SWA from the meter box terminates in an adaptable box in the upstairs services area. The tails then run out to a meter that I installed simply because it has a data port that will allow me to monitor and log the energy consumption of the house. The PV import meter is right next to my monitoring meter, which is next to the internal AC isolator for the PV system. The consumer unit has RCBOs on every circuit, something very well worth doing for several reasons. Firstly, it means that a fault will only trip one circuit in the house, which is less inconvenient and makes it a bit easier to find the fault. The second very good reason is safety related. If you have a PV installation then the inverter can continue to supply power to the consumer unit for up to 5 seconds after the mains supply is disconnected (say by an RCD in a conventional 17th edition split board). This can then, potentially, create a situation where the RCD trips because someone’s had an electric shock (and they are designed to trip fast to prevent death, 30mS) yet the PV inverter carries on supplying power to the side of the board that’s tripped out for a few seconds. My personal view is that this is very iffy, but an all RCBO board circumvents this risk, even if it is a fairly small one.  There is a DP time delay RCD as the master, just to catch the near-impossibly rare faults that a SP RCBO won’t always catch, but as my electrician said, it’s total over-kill for the sort of installation we have.

This black box:

is the home made PV diverter. This works like an Immersun Mk 2 and diverts excess power from the PV array to the thermal store (the green thing to the right). Whenever the PV power generated exceeds the house power demand the excess is fed to the immersion heater in the thermal store, providing most of the hot water for the house, free of charge. We still get paid for generating power, on the basis of 50% of the deemed generating capacity of the PV system, whether we export that power or not, so it makes financial sense to use it, rather than export it. In practice we’re still going to export a fair bit of power, as even on a dull and rainy day like today we generated around 8 kWh, more than we’d need for hot water.

The UFH heating isn’t filled and commissioned yet, but the pipework and controls are all finished and tested. This is the weather compensated, sensitive thermostat I made to control the circulating pump:

The thermostat measures the outside air temperature, via a probe on the North side of the house, and the slab temperature, via a probe set near the centre of the slab. It has a switching threshold of +/- 0.1 deg C and is designed to hold the slab at an accurate temperature of around a deg or so above desired room temperature. It does weather compensation by increasing the slab temperature by 0.1 deg C for every 1 deg C drop in outside temperature below 5 deg C. I can change the slope of this characteristic and anticipate I may need to fine tune it to get the house temperature to remain stable. I had to go down this route because a conventional thermostat would have had far too great a hysteresis (the difference between the turn on temp and turn off temp), and could have resulted in large swings in room temperature (one of the problems with controlling a passive house is supplying just then tiny amount of heat needed, very accurately).

Finally, here’s a bit of the kitchen bling:

This is an Itho stainless steel boiling water tap. The right hand lever is a normal hot/cold mixer, fed from the hot and cold supplies, the left hand knob (with a safety button) is the boiling water dispenser. This means that we have no need for a kettle, and can make tea straight from the tap. The boiling water is provided by a very well insulated pressurised boiler that sits under the plinth:

It’s fed with softened water by a small under-sink cartridge water softener, on the left in this photo:

Getting everything neat and tidy under the sink was a struggle, as I wanted to try and leave as much useful cupboard space under there as I could. Being able to put the boiler unit under the plinth was a great help, as it would have taken up loads of space in the cupboard. I may swap out the switch for the boiler for a time switch, so that it’s only on when we need it, which is mainly during the day (when the PV will, hopefully) be generating. It only uses 32 Wh of energy on average, though, so wouldn’t be a massive cost even if we left it on all the time (especially as we’ll still be net exporters of power over the year,anyway).

I should have some photos of the completed water treatment plant soon, it’s nearly finished, and with luck will be commissioned tomorrow.


ProDave 23 Apr 2014 07:13 PM:

 Excellent stuff.

 That costing spreadsheet is a great help for costing my build. Since I’m going down the route of getting one person to design it and then another to build it, with me doing all the finishing off, it will be a bit hard to cost. And the first time I’m going to need an accurate costing is for the building warrant application, where the fee is based on the cost of the building work.

 And yes there’s a lot in your single meter box. Did the meter monkey say anything? sometimes they get a bit uppity if they think there’s too much stuff in “their” meter box.


 slidersx200 23 Apr 2014 07:24 PM:

Interesting reading as usual Jeremy and once again you have been very open in sharing your experiences of the actual costs associated with specific elements of the build. How did you fair with the PV system if you don’t mind me asking? It’s currently on our “if we have ANY money left” list, but I’d like to ensure the heating/dhw system is designed to take advantage of it in the event we do fit it someday.

 Slightly off topic perhaps, but your mention of the temperature probe in the slab got me thinking about how much of the plumbing, electrics etc need to be installed before the slab is poured. I know quite a lot can be accommodated in the service void or internal stud walls, but no doubt some items will need to go through the floor and as (if I understand correctly) when using the Viking House/Supergrund type systems the finished floor surface is poured before the frame is erected, quite a lot of decisions will need to be made very early in the construction stages.


 jsharris 23 Apr 2014 08:03 PM:

 Dave, the meter guy had a moan, but I just said that it was my box, I’d paid for it and installed it, and that there was loads of room for the company head and meter (this was before I’d fitted the fused isolator at the top right…………….).

 Suzanne, you really need to think ahead and get as much as you possibly can come up through the slab. This means a lot of very accurate setting out, as you need to be certain that the soil pipe(s), water pipe, electricity supply, phone cable etc are all in the right place inside the house. I opted to have just a single soil pipe stack come up through the slab, by deliberately designing the house so that all the toilets (on both floors) were located near to a single point, which meant having to only have one waste pipe (for the kitchen sink and dishwasher) go out through the wall. This significantly reduced the heat loss from having too many holes in the building.

 The temperature probe was added afterwards. The MBC guys marked where the UFH pipes were (plus I had photos) so it was easy to drill a hole into the slab in a safe place and grout in the probe. I did this as part of first fix electrics, and fitted two sensors, with the cable from the spare one coiled up in the eaves (in case one of the sensors fails).

 PV is an absolute no-brainer. Just do it. Ours is generating loads of power (it’s now over 700 kWh since going live on 20th March). It was also relatively cheap, certainly given the amount of energy it will produce over its lifetime, plus the FIT payment. The pay back time, just on the FIT payment, will be around 7 years, and that ignores all the free energy we’ve made use of for hot water.


 joiner 24 Apr 2014 06:59 AM :

 All good stuff!


 coopers 24 Apr 2014 09:57 AM :

 “Suzanne, you really need to think ahead and get as much as you possibly can come up through the slab. This means a lot of very accurate setting out, as you need to be certain that the soil pipe(s), water pipe, electricity supply, phone cable etc are all in the right place inside the house. I opted to have just a single soil pipe stack come up through the slab, by deliberately designing the house so that all the toilets (on both floors) were located near to a single point, which meant having to only have one waste pipe (for the kitchen sink and dishwasher) go out through the wall. This significantly reduced the heat loss from having too many holes in the building.”

 I think this was meant for Sliders (Michael), who’s not wearing his dress today.

 All good info J, and really useful for all us would-be-passive-house dwellers. I’m sure you’ve done the energy efficiency calcs on boiler tap vs kettle?


 jsharris 24 Apr 2014 05:18 PM:

 Sorry Suzanne and Michael – I blame it on one too many glasses of “relaxation” after a particularly busy day……………


 wmacleod 24 Apr 2014 08:30 PM:

 “ProDave, on 23 April 2014 – 07:13 PM:, said:

 And the first time I’m going to need an accurate costing is for the building warrant application, where the fee is based on the cost of the building work.”

 Dave, I don’t know if you will be allowed to use your own costings for the work, I certainly wasn’t when I questioned it, I had to pay the fee based on £1136m2 for the ground floor and £813m2 for the upper floor unless a certified chartered surveyor would go over my costings and sign off on them. Fees for that would have been more than the difference in the building warrant fee!

 Pictures look great Jeremy, it is really interesting to see the build progressing so well. The breakdown of the costings is very helpful as well.



Alphonsox 25 Apr 2014 09:15 AM :

 Many thanks for sharing so much detail. It is proving extremely useful for getting our build up and running.

 A couple of questions…

Does the £53K MBC cost include the cost of the garage timber fame ?

What controller did you end up using for the UFH ? some form of PID ?


 jsharris 25 Apr 2014 04:16 PM:

 No, that was just the cost of the house foundations and frame. The garage frame and insulation was about £7k, and the slab and ground works for it was another £1600. The garage is 6.1m x 4.1m and is lined and insulated, with a floored out storage loft, so I can use it as a workshop.

 The UFH controller is just a simple on/off thermostat, with a +/-0.1 deg C switching threshold. The time constant of the slab is such that there didn’t seem any merit in doing anything more sophisticated, although it’s very much an experiment, so I may be wrong. All the controller does is turn the UFH pump on and off. The UFH flow temperature is fixed via the mixer valve (which can be adjusted to give me control over the warm-up time). The calcs show that with a 25 deg C flow temperature the warm up time should be about 1/10th of the cool down time at maximum heat delivery, so I’m hoping that this simple approach will do the job.


 coopers 28 Apr 2014 07:01 PM:

 Hi Jeremy,

Was the house fully battened ready for tiles? Today I spoke to our preferred builder, who will be doing all the non-timber frame details. He expressed concern that the roof will be felted and battened. He said it’s a recipe for disaster, as if the battens aren’t properly aligned, the roofers will have to rip it all off. He said if they are fly battened, then it’s ok. I’ve tried to look this up, but I’m not getting anywhere.


 jsharris 28 Apr 2014 07:23 PM:

 Yes, it was fully battened exactly to the right spec for the slates we used. I just ensured that MBC had the correct batten spacing, including the shorter spacing for the first batten (to allow for the 50mm overlap in to the gutter).

 Not at all a problem, the roofers had no problems at all with fitting the slates properly, as all the battens were exactly where they should have been.

 I’d question the wisdom of your builder, as he clearly doesn’t seem to understand quite how accurately built one of these houses is (and needs to be). As another example of accuracy, I double checked the finished dimensions of the downstairs WC last week (in order to order units). I designed it to be 1210mm wide (to allow for two 600mm wide units with enough room to fit them and allow for any slight errors in squareness). The room turned out to be 1211mm wide with dead square corners.

 Do NOT accept it being fly battened, the battens need to be fixed on the correct centres to the counter battens at the first go, as they are nailed through the special breather membrane (it’s not felt). All you need to do is let MBC know the pitch required for your chosen roof covering (including the offset lower batten) and they will do the rest, to a very high spec.


 coopers 28 Apr 2014 08:21 PM:

 ah, I see, that makes sense. He was saying that if a house isn’t square, it will show in the tiles more than anywhere else. I guess he’s used to building wonky houses!!

 Thanks Jeremy



28 Apr 2014 08:39 PM:

My experience has been that pretty much every trade I’ve had on site has been amazed at how accurate and square the house is. British builders are clearly more used to houses being built to much poorer levels of accuracy, which undoubtedly leads to many of the problems we have with poor airtightness and thermal detailing with so many British built houses.


 eddleetham 29 Apr 2014 06:58 PM:

 Jeremy, I’ve been struggling with making comparisons between different timber frame manufacturers’ quotations, as they all seem to have slightly different specs. When I spoke to Seamus he helpfully suggested that his quote would be roughly half the cost of the finished building. It’s obviously only a ball-park figure, but would you agree that for a straightforward build without any major site problems, and assuming an average quality of finish, that’s a reasonable estimate?




 jsharris 29 Apr 2014 07:29 PM:

 Hi Edward,

 I think that, for a very basic finish, then it might “just” be possible (at least in cheaper labour cost areas of the UK) to build for this sort of cost, but it would mean a fair bit of DIY.

 I think it’s pretty hard to get any self build in the UK, especially in the south, to come in under £1000 sq m, and most average builds seem to come in between £1100 and £1300 per sq m. The cost of our basic foundation and insulated frame from MBC Timberframe came in at around £400 per sq m; others here have had quotes for simpler builds from them that have been closer to £350 per sq m.

 I think there’s no substitute for doing a detailed costing, including as much detail as you can. One major problem I found when trying to do this, was that many of the frame suppliers were very unclear as to what was included or not included. More than once I thought I’d found a bargain, only to find that when I costed in all stuff that wasn’t included the true price was way over the attractive quote.

 My feeling is that the finished cost is going to be around 3 times the foundation and insulated frame cost, even for a fairly basic finish.


 coopers 29 Apr 2014 07:39 PM:

I agree with Jeremy, at least 3 times the frame/slab/insulation costs.


 TerryE 10 May 2014 01:11 PM:


 Since I will be doing my own spreadsheet, I pasted yours into OpenOffice Calc and rechecked the totals to make sure that I hadn’t made a mistake. In doing so, I noticed that you’d missed out a subtotal for Floor coverings, which carries through to your grand total. Shock, horror, I’ve just added £4,976.41 to your total build cost. Sorry 

 But v. useful. Thanks.



10 May 2014 01:40 PM:

Well spotted!

 Thankfully it’s only on the cut down and heavily edited version I posted here, the main spreadsheet I’ve been using has that sub-total included. Somehow I must have accidentally edited out that sub-total when producing the version I uploaded here.

 I’ve now edited the version in the post above to reflect the true cost!



 pocohontas 16 Sep 2015 01:28 PM:

 Sorry if you’ve written this elsewhere – did you get the Vat back on the MVHR? I’m looking at getting a few things from Europe.



 jsharris 16 Sep 2015 06:45 PM:

 I’ve not put the claim in yet, but I did call HMRC and they confirmed that I could claim the Danish VAT back, as long as I included evidence of the exchange rate at the date of purchase.

 Others here have claimed the VAT back on purchases made in the EU. I think Colin (temp on here) claimed back the VAT on stuff he bought in the EU.


Part Twenty Eight – 90% Finished, So Only Around 90% Left To Do…………

This twenty eighth entry was published originally by JSHarris on the 19th April 2014 and received 1,442 views on the closed forum

I know one shouldn’t ever start with an apology, really, but in this case it’s so long since my last update that I feel one is due. Several things conspired to delay this entry, ranging from getting pretty stressed out with the build a while ago, to smashing my camera on site and not being able to take photos. I’m pleased to say the stress levels have dropped, and as those who’ve popped in over the past few weeks will know, a fair bit of progress has been made.
I’ll start off with some photos to give an idea of the transformation that’s being going on. This is the view through the front door, with the hall decorated, the travertine flooring down, the oak doors and staircase in place, but without the glass balustrade panels fitted:

And this is the view looking the other way:

The underside of the staircase has a 6mm rebate routed in to the inner edges of the string, so that I can panel it with some 6mm oak veneered ply. The staircase manufacturer has thoughtfully provided some wedges, cut to the exact staircase angle, to glue and pin to the lower edge of the underside of the risers to support the centre of this panel

I spent a happy week fitting the kitchen units and plumbing in the integrated dishwasher, boiling water tap etc, plus doing the necessary wiring for the induction hob and cooker. We’re still waiting for the combination microwave to arrive, and the stone fitters have yet to fit the upstands and window cills, but this is how the kitchen looks at the moment:

Once we’d had most of the second fix electrics completed I arranged to get the PV system wired in and connected (on 20th March) so we just managed to get our system registered and beat the FIT tariff change at the beginning of April. As of yesterday afternoon when I left the site (just after 4 weeks after the system was commissioned) it had generated just over 620 kWh. It’s peaking at over 6 kW most days, and even on dull and cloudy days we seem to get around 1 kW or so from it much of the time. It looks as if our predicted generation for the year of around 7,000 kWh is about right. The inverter had to be mounted on the outside of the house, on the North wall, as it generates a fair bit of heat when working at full power, the last thing we want inside the house in mid-summer. Here’s a photo of the inverter, tucked out of the way around the back of the house:

I’ve also hooked up the ASHP, and fitted it under the inverter around the back of the house. It’s bolted down to some concrete blocks laid on their sides, which in turn are mortared to the retaining wall foundation slab:

The ASHP was dead easy to install, just a flow and return pipe (like a boiler) a power feed and a four way control cable. I’d already fitted ducts through the insulated wall for these connections, so ran the pipes/cables through then sealed up around them with squirty foam. The hardest part was fixing and insulating the large bore flexible flow and return pipes, as they are tucked away at the back of the unit and tricky to get at.

When I came to fit the buffer tank I discovered that it wasn’t a direct one as ordered, which caused a bit of head scratching at first. It seems that the manufacturer had accidentally fitted a 7kW coil in the buffer, making it an indirect one. After a bit of discussion with the tank supplier, and a few calculations, I decided that an indirect buffer was actually an advantage, as it allows me to have a very low volume primary circuit, which in turn means a massive saving in antifreeze cost (well over a £350 saving). In terms of extra complexity, it’s meant fitting an 8 litre pressure vessel and filling loop up in the services area, plus an extra bottle vent, but it does now mean that the main thermal store, buffer tank and UFH circuit can be filled with ordinary water plus inhibitor.

I’ve got all the buffer tank plumbing completed and have started plumbing in the thermal store (which should be dead easy, just a cold and hot water connection, plus the two 28mm thermo syphon pipes from the buffer and an overflow. I’ve run a length of 32mm waste pipe down from the first floor services area, behind the buffer tank and then along the wall to a trap, then the washing machine drain another trap and the connection to the main soil pipe stack. This waste pipe will take the overflow from the thermal store header tank and the two condensate drains from the MVHR unit, once I’ve figured out the easiest way to connect three 20mm pipes to a vertical length of 32mm pipe.

One small issue I’ve had is with sediment in the borehole. This was, to some extent, to be expected, as the upper layers the drillers went through were fine grained gault clay/mudstone, and they were wet drilling, so were pumping a lot of the black muck back down the hole to clear the debris out. The water runs crystal clear if left to run for a few hours, but when turned off and then on again it is sometimes a bit murky for a few minutes, before it runs clear again. I knew I’d need some sort of filtration system, but to work out which would be best I needed a water analysis. The local authority are obliged to offer a water analysis service for a fixed price of £25 (the rate’s set by central government), so I emailed them and rang them to find out how to get a sample to them for testing. This was the first time I’ve encountered the sort of bureaucracy that local government is infamous for. It turns out that they will test the water for £25, but won’t accept a sample that’s given to them, they insist on coming out and taking the sample themselves, for a fee of £100 on top of the analysis fee. The (rather unhelpful) chap in the Environmental Protection team told me that this was because the water analysis cost the council around £70, so if they didn’t charge the sampling fee they would lose money on every test. Clearly what they were doing was circumventing the governments intention to make safety testing private water supplies affordable, by setting the maximum fee at £25. In reality they were charging the £70 analysis cost, plus another £55 to call out and take a 2 1/2 litre sample of water. Not only that, but they insisted that they could only take a sample from either a kitchen tap or from a special sampling tap that was installed within a covered area. As I only have a standpipe in the garden this would have meant additional expense in sorting out something that met their requirements.

Luckily there’s a place just up the road from me that offers very sophisticated analysis capability if you ask the right person, so I took a sample, gave it to this “right person” and within 24 hours had all I needed to know to choose the right sort of filtration system. Our water is fairly alkaline (pH of 7.6) with a fairly high total hardness of around 260. It also has a fair bit of iron in it (0.22 ppm) and a tiny trace of hydrogen sulphide (0.2 ppm, which is way below the harmful threshold of around 5 to 10 ppm). The latter can be smelt when the water first runs from the tap, but isn’t at significant levels in terms of health risk. The iron level is on the high side, though, the recommendation is that iron in water shouldn’t really be above about 0.05 ppm and it would be a good idea (just for the sake of taste) to get the level of hydrogen sulphide below the human smell detection threshold of around 0.005 ppm.

Getting rid of this low level of iron and hydrogen sulphide is very easy, and can be combined with a filter to remove the fine sediment. Getting both the iron and hydrogen sulphide out relies on oxygenating the water, then passing it through a filter bed of manganese dioxide, with sand and gravel at the bottom. This works catalytically to remove both compounds, with the resulting sediment build up in the filter being removed by backwashing it to the drain every couple of days. All this happens automatically, with the filter media being held within a tall pressure vessel (rather like those water softeners use), fitted with an electronic control head and timer that periodically backwashes and regenerates the filter (by allowing the filter vessel to fill with air) at a set time (by default it does this at 3 am every other day). I’ve fitted this in the lean-to water treatment plant shed I built on to the back of the house, so we shouldn’t be aware of it flushing . Luckily we’d already run a length of perforated land drain pipe from the big soakaway under the drive along the back of the house (to take the run off that tended to collect on the retaining wall slab foundation) and the end of this was just below the water treatment shed. All I needed to do was push a long length of 25mm MDPE pipe down inside it and connect this up to the backwash drain outlet on the filter (the filter backwashes under pressure, so water flows out of this pipe under the pump pressure). I still have a bit more plumbing to do with the filter, but have got most of the connections made.

Getting water into the house will be a big step, as I can both start checking all my second fix plumbing for leaks and can get the downstairs WC working, which will save the cost of the portaloo hire. Once that’s gone (and the skip’s gone) I can take the Heras fencing down. By pure luck another self-builder a mile or so up the road wants to buy all my Heras fencing (as they are hiring at the moment, and realising how hire costs add up), so the timing couldn’t really be better. I’m looking forward to getting the fencing down and the skip and portaloo out of the way, as it makes the place look so untidy.

We’ve had a fair few visitors since the last entry I made here, including two visitors from the local authority, the Sustainable Energy Across the Common Space lady (see here: and the Energy Policy Officer for Wiltshire Council (who is also an enthusiastic AECB member). As a consequence our home is now part of an initiative to raise awareness of energy conservation measures in the home in this area, the South Wiltshire Green Doors programme. We’ll be open to show people around over the weekend of the 17th and 18th May, but visitors have to book through the Green Doors programme, here:

I’ll try and make updates to this blog a bit more regularly from now on…………………


ProDave 19 Apr 2014 08:22 PM:

I was wondering how the “black sludge” episode with the water was doing. Did fitting a timer work to purge the remaining sediment out and does it now run visibly clear?


 jsharris 19 Apr 2014 09:02 PM:

It’s a bit variable, Dave. Sometimes it runs clear within a minute or two of turning on, sometimes it takes two or three minutes or more before it runs clear. It pretty much always runs clear within 5 minutes, so I’m far from sure quite what’s going on.

I know that the borehole is down into a major aquifer, as even pumping at 1200 to 1500 litres per hour doesn’t drop the level at all. It may be that there is enough “cross flow” down in the bore to disturb the sediment, and may be this varies a bit from day to day. The general consensus from those I’ve spoken to is to just filter it out and backwash it to a drain every few days.

As I need to treat the iron in the water anyway, and as this treatment system needs backwashing every couple of days to regenerate the media, I’m just going to go with this as the main filter. I have plumbed in a Cintropur centrifugal filter, with a 25 micron screen before the main manganese dioxide/sand/gravel flter, as a way of collecting some of the sediment in a clear filter bowl to keep an eye out for any changes. This Cintropur filter has a drain port at the base and I’m thinking of fitting a solenoid valve to this, so that I can get it to blow out any muck for a couple of seconds whenever the pump turns on.

I have a feeling that I may have to just live with the water being a bit cloudy as it comes in, and let the filters sort it out. This is pretty much what the water companies do in many areas, anyway.


 Nickfromwales 20 Apr 2014 08:47 AM :

Hi Jeremy.

The house is looking great. The travertine is really nice, I’ve just done a hotel entrance lobby with the commercial grade honed and polished stuff with mosaic ‘doormats’ outside each door and by the entrance door. Looks stunning when the light hits it the right way. Don’t forget the impregnator sealer!

Is the inverter IP rated or is it going to be protected from the elements by a cover / other ?

The overflow pipe from the store goes to a trap, you say. Is it by luck or engineering that you have the two condensate overflows going into the same 32mm pipe? The reason I ask is I’ve seen plenty of overflow pipes which go to a trap before terminating to a soil / stench pipe. The problem is that there is no regular / occasional water flow through the pipes to replenish the body of water in the trap (which eventually evaporates and leaves the trap empty) so the stink from the soil pipe is free to come back through the empty trap and cause nuisance smells / draught etc.

Do the condensate outlets discharge water periodically throughout the year? I imagine you’ve engineered it but curiosity has the better of me!

Regards, nick.


 jsharris 20 Apr 2014 09:30 AM :

Thanks Nick. The travertine does look good, but I was a bit annoyed at the way the estimating guides for calculating the amount of adhesive, grout and sealer worked. We ended up with 7off 20kg bags of adhesive, 4 off 10kg bags of ivory grout and around 6 litres of (very expensive) Lithofin sealer left over. We sealed the travertine after fixing it down, but before grouting it, then sealed it again after grouting. I’ve got enough left over sealer to do the whole floor another couple of dozen times, I think!

The inverter is IP65 rated, so OK for outdoor mounting (it’s specified as an outdoor model). Another advantage of having it outdoors (apart from keeping it cool) is that it makes a definite buzzing noise when running near full power. Not enough to be a nuisance outside, but I think it would be audible inside the house and might be a nuisance.

It’s engineered to have two traps in series, Nick, as I strongly suspect that the tank overflow/MVHR condensate drain trap will be dry from time to time in the summer. The 32mm pipe runs down from the service area (where the three drain outlets need to be hooked up to it somehow) to the first trap, and then along the wall under the work surface in the utility room, where it connects to a 40mm waste and trap for the washing machine. This 40mm waste then runs across to the main soil stack in the downstairs WC. The idea was to avoid having holes through the external walls as far as possible.


 coopers 23 Apr 2014 08:04 AM :

Nearly there Jeremy. Any more pictures of inside and patio doors etc? Is the window colour silver or grey on the MJ chart?


 jsharris 23 Apr 2014 05:22 PM:

Hi Suzanne,

I’ve taken some more pictures for the next blog entry, but they are really showing some of the technical stuff. The windows and doors are dark grey, RAL 7015, outside, plain lacquered pine inside.

There’s still a great deal to do, and it’s all down to me, so is going slowly! I’m hoping to get the water supply in and working this week, and then get the downstairs WC in and working next week, along with commissioning the MVHR and perhaps the ASHP. After that I still have to fit out both bathrooms, lay all the bamboo flooring, fit all the oak skirting and architrave and fit out the utility room. I can spend a whole day working non-stop at the moment and nothing much looks any different afterwards!



 coopers 23 Apr 2014 07:59 PM:

It will be fabulous! What made you choose the bamboo flooring? We’ve no idea what we will have yet.


 jsharris 23 Apr 2014 09:06 PM:

I do hope it turns out OK………..

The choice of bamboo was primarily because it is very, very hard. This means it’s harder to dent or mark (although it can still be scratched) than wooden floors. It’s also fairly thermally conductive, and when glued down (rather than laid as a floating floor) it works well with UFH. Finally it’s relatively inexpensive (around £20/sq m) and has great eco credentials (as it’s grass, and grows very quickly, locking up a fair bit of CO2).


 couplands 28 Apr 2014 01:38 PM:

Hi Jeremy, I note you say glue the bamboo flooring down. Is that because there is little need for expansion in your house due to stable temps..?

I have generally laid floors loose/floating in the past. Not that I’ve laid a lot of floors..:-)


 jsharris 28 Apr 2014 03:10 PM:

Apparently gluing the floor down still allows expansion, as the adhesive is a modified silicone, so remains flexible. You still need to leave 10mm expansion gaps around the outside when using the adhesive, just as you do when laying a floating floor.

My reason for gluing it down (at least on the ground floor) is because it reduces the thermal resistance, so the the UFH should work a little better. It also makes the floor feel more solid, I’ve been told, and with plain T&G flooring it avoids the need to glue the tongues with a bit of PVA when laying. The downside is that the adhesive is expensive. I’ve gone for Sikabond T54, which is specifically designed to allow floor natural movement.


 ProDave 03 May 2014 06:37 PM:

I’m after more details of your ASHP. I’m leaning more towards that and abandoning my plan to use ground source.

 So yours is “monoblock” so it’s all in one. So it just sits outside, extracts heat from the air, and sends that to the house via flow and return hot water (circulating antifreeze) is that right?

 How noisy is it? If I choose that it would go under the car port the far side of the garage to keep it as far as possible away from the house as we don’t want to be able to hear it. Alternatively can it be wall hung on the garage gable end above the car port (if there’s any technical reason why it might not work well under the car port)

 This would mean fairly long flow and return pipes. I guess that just means a bit more antifreeze needed and not other issues as long as they are well lagged?


 jsharris 03 May 2014 07:42 PM:

Yes, a monoblock is pretty much the same as a boiler, just a water flow and return plus power and control wiring. The water needs antifreeze, solely for the case where the temperature drops below freezing and there’s a power cut, as when there’s power the unit has freeze protection (by just running for a short time at very low speed to keep itself warm).

In the end I bought a new Glowworm 7kW Envirosorb2, for £1700 inc VAT and delivery. It came with an internal programmer/control box, that’s connected by a four core low voltage cable. It’s a massive overkill for our needs, but there was nothing that came close for an equivalent price.

It’s very quiet, unless being asked to deliver high temperatures, when it does hum a bit. I accidentally set it to deliver 55 deg C flow temperature when the outside temperature was around 8 deg C, and it was noticeably noisy outside, but I couldn’t hear it at all inside, even right by the wall where it’s mounted. It’s about a metre from our back door and maybe 300mm from the rear wall, mounted on blocks mortared down to the retaining wall foundation. This meant very short connecting pipes, and as this is at the back of the house it’s well away from habitable rooms (the living room is the other end of the house at the front). There’s no need to run it at night, as the house will maintain night time temperatures from the residual heat in the slab and the heat in the buffer tank.

I’d not wall hang it, as I suspect it might transmit vibration into the structure. Better to bolt it down to solid concrete and isolate it with large bore flexible hoses. I very much doubt if you would be able to detect it running from inside the house, even if it was mounted just the other side of an external wall. If you really do need to position it so there are long pipe runs, then you could look at running them in very well insulated ducts under the slab, as that might reduce the losses in very cold weather. I’d also think twice about fitting it under a car port, as that might tend to amplify any noise. I’m sure ours sounds noisier than it really is because it’s in the deep corridor at the back of our house, between the house and the retaining wall. This means that the retaining wall tends to reflect any noise back to the house, yet still I can’t hear it inside when it’s running at 40 deg C flow temp.

 The secret to keeping the noise down seems to be the inverter technology. Ours will run with the fan barely ticking over, or even stopped, when only asked to deliver a few hundred watts. AFAICS, it’s a bit like a very wide range modulating boiler, and is capable of running from a few hundred watts output up to about 8kW output when the conditions are right. It heats a 70 litre buffer tank from cold to 40 deg C in around 20 minutes, and that’s then enough to heat our house to 20 deg C when it’s 10 deg C outside for a several hours. When working at this flow temperature the fan on the unit is barely spinning, and it seems that the fan is the major noise source.

If worried about noise then I’d be inclined to look at over-sizing the unit. You might lose out a little bit on efficiency, but gain by having the fan only run very slowly most of the time.