TerryE

The sort of Σ( area × U-value × ΔT) calc that I did in the blog entry below for Jan daily ΔT average and maybe by month should be within 10% and the following one. It is certainly enough to explore marginal infrastructure costs and heating run-rate costs. This is of course assuming that as-build performs broadly as-designed, that you haven't introduced any bridging or insulation flaws. PHPP introduces 2-D adjustments such as Psi-values, but TBH, if these are at all material then you've done something wrong in your wall / ceiling / slab mate-up.

@SteamyTea, One of the strengths of the StackOverflow sites is that if I am learning about a new topic, then I will do a search by descending votes on the associated tag and then scan through the questions and drill down on any that look interesting. The nearest that we have is the "Sort by" selector which allows you to sort topic by #comments and #views descending which does tend to hoist the most valuable topics to the first page or two. On another forum that I used to be a moderator on, the mods introduced a "Moderators Picks" pinned topic which was a list of interesting / best topics for that sub-forum. The trouble with doing this is that it is high maintenance and gets misleading if not regularly maintained. Note sure that we can square this circle.

No apologies asked for or needed. I am just trying to say that there is a lot of gold and gems there – in terms of useful knowledge and experience – amongst threads and blog posts. Well worth mining! 😊

@AccidentalSkydiver, If you don't want to go the supplied TF route, then I feel that following @ProDave's approach of buying in (mostly) pre-cut 8×2 or engineered equiv, then making up cassettes onsite for onsite erection might prove the best choice for you. External panelvent board-out and 100mm external insulation; breather membrane, of coarse just remember to mark off the verticals lines on the outer -- this makes fitting wall ties a lot easier as they do need to be fixed the joists and not just the panelvent 🤣. If you go for pumped cellulose, Then you can internal board out with OSB3 as you go along to give racking strength, then do the pumping before 1st fit. Of course, you will probably need an SE to sign-off on the entire structural design for B Control approval. One other thing if you go this route: go for a warmslab foundation if you can -- with integral UFL loops in the slab. Look on the blogs and YouTube. Search for the company that we used: MBC. I am not saying that you should use them (though they did do an excellent job for us) -- some members here (e.g. @Stones) went this route DIY, but these videos and blogs give you an idea of what I mean. Having the entire base to FFL with a +/- 2mm accuracy gives you a clean datum for cassette make-up and frame erection. 2×6 vs 2×8 is mainly a structural design issue for your SE, I guess.

Rishard, I am not trying to be difficult here, but you have to remember this is a pro-bono community. The regular posters who answer most questions tend to get pretty fed up answering some subtle variant of the same Q for the 20th time. I always search a forum for the answer to a Q before asking. 90% of the time good Q and A resolves my issue, and when I do ask it is on some specific point that is more likely to get an answer.

Rishard, These sorts of Q aren't needed if you can use the search facilities, on forum and Google. 30s to ask this sort Q and how much time do expend other members to spend answering?

@Marvin, I just cranked the maths on the figures that you provided, not on my figures. For my own house the numbers are a lot more compelling. I have a 3 storey house with ~ 250m2 floor-space with UFH on the ground-floor slab only. The inflow on the MHVR inlets is around 19°C, but we keep our internals at around 22½ °C. We don't have any heating on the top two floors (except a couple of small oil filled rads which my HA system turns on for a few hours every night during the coldest three months). If the 0.5 ACH was coming in at 0-5°C overnight instead of 19°C, then we would have needed some form of decent CH system for the top two floors. You just can't look at one component and try to optimise it in isolation (not unless your name is Boris 🤣). You have to treat the house as a whole. You also can't just use averages, because if you want to avoid freezing your bollocks off, then your system still has to cope with that Dec-Feb window when the night temperatures can hover not too far above 0°C. We did our MVHR for ~£2K, labour DIY. We avoid maybe £4-5K of CH costs and needing to install gas, etc. Ignoring the avoidance of replacement CH solutions, the payback period was under 3 years. As well as living in a fresh damp-free environment. IMO, this one was an absolute no-brainer. You do need reasonable access for maintenance / cleaning, say once a year or so.

IMO, they are easier to balance and a lot easier to run: no pipe Ts or joints; just a 1-1 from the central manifold to the individual vent,

Pretty much identical to mine except that I put the manifolds in a cupboard in the loft so the pipe go down into the floor rather than up into a wall

If you want an installer to take design authority and prepare the building control documentation and certification, then this is one valid route but I feel you should expect to pay ~2-3K for this service plus typical manpower rates for installation. On the other hand if you want to DIY, then I suggest that you need to take design authority and do your own calcs. IMO, BPC provide a useful design validation, but it's essentially a "free" service funded on their supplier margins. Having 4m high ceilings is the sort of thing that they might miss when working from plans. Again, this is a common theme discussed in the past. The BReg ventilation reqs are rather high in terms of volume exchange. A lot of us cranked the flow-rates up high to do the certification report, and then dialled the rate back (say to 30%@ normal; 50% @ boost) for living in.

We used these guys: BPC. I got them from others on this site who recommended them. I downloaded all the manuals, installation guides, etc, and dis my own design but passed it past them for validation. They suggested a few tweaks on vent placement, but OKed the rest.. Others just shipped them their house plans and asked them for the layout and equipment list. They then shipped us everything on a palette. Based on a couple of spot-checks, they were pretty competitive (this was ~5 years ago). As I said above we did the install ourselves as part of 1st fix and commissioned the system pretty soon after the the internals were plastered out. All pretty straightforward, really.

Conor, You've got your commission order out of sequence. MHVR should have been just be about the first thing to commission after 2nd fit as soon as you have a temporary electricity supply up. Pretty much everyone here on the forum (at least those that have sized and commissioned their MVHR systems correctly) agree that you live in a house that always smells fresh and that never have problems with damp or condensation. The tickle vents and four holes will be a PITA to seal properly once your MVHR is commissioned. The MVHR system was one of the things that Jan and I did ourselves. The sizing calcs are straightforward as is a star manifold installation, though to do need to properly calibrate and commission the system. If done properly, the B Insp will accept a self-certified commissioning report. It performs really well.

SHair ~ 1 kJ/kg/K, Densair ~ 1.2 kg/m3. So 108 × 24 × 14 × 1.2 × 1 /3600 = 12 kWh Yes you are correct in that it is not ½kwh / day. It is roughly 25× that. Your inference is wrong. In a near passive class house, air losses are by far the largest heat loss component if you don't install MVHR.

Much as with @Temp and @Russell griffiths we have a warm-roof, where the roof profile was sarked, partly for structural reasons (to give racking stiffness to the loft storey) and partly just to provide a physical barrier between the roofing and the house interior. This was then "felted" with roofing membrane and vertically battened. The slater later added the horizontal counter battens in line with his slating plan. We had a continuous horizontal breather at the eaves and under the ridge tiles to facilitate airflow between the felt and the slate to keep the under-slate area ventilated and dry.

I understand where you are coming from and you clearly have to guard against potential poor workmanship, but IMO that's a matter quality control and not a cause to accept that you've lost control of your subs before you begin.

Ours is -- by the MVHR -- because the top floor in the roof is part of our living space. One a more serious point, having a ventilated cold roof is one approach, but not the only one from a design and construction PoV -- Yes, you've got to get the thermal design, RH gradients vapour barriers etc correctly placed, but this is all entirely doable and we've talked all of the issues to death on previous threads on the forum. The main advantage of a cold roof is that poor builders are less likely to screw it up.

Have a read through my blog @Jeremy Harris and others. You have Slab losses, wall losses, fenestration losses, roof losses, air exchange losses, and thermal bridging losses. You need to design a house with a sensible balance to optimise so that you get a delta £s invested on any one that gives the best drop in heat losses and therefore delta £s in running costs. As with my and Jeremy's calcs, you don't need anything too sophisticated like the PHPP model which as so many terms and adjustments that it is intractable to make trade offs. With TF, as Dave says 8×2 + an extra layer of slab insulation can get a U-value of 0.12; slab and roof same ballpark; decent triple glazing under 1.0. Once you are in this domain 40+% of your heat losses are from air exchange if you have a pretty airtight house and MVHR; up to 85% if you use poor quality conventional build techniques and no MVHR, so you need to make your house airtight by design. The MVHR means that it always smells fresh because you are continually replenishing with (reheated) external air. If doesn't matter how good the nominal design is if your builder doesn't bother putting in the roof or wall insulation where you can't see -- as many have discovered with a FLIR camera once they've moved in. Ditto thermal bridges on steel I-beam crossing the warm / cold divide. The single biggest cost component in our house was the natural local stone skin -- which was a planning requirement, as well as looking nice. As to the near-passive performance, adding this was maybe 15% of the cost of the skin, but then again I use a 3kW inline heater to heat my water-based UFH system and our internal temp is ~ 22½°C everywhere, all year round. Putting the water-base UFH loops in the slab cost ~$2K and no other CH installation, rads on walls etc needed. (The 22½°C is because a pair of OAPs like it that way.)

An estate agent gave me a piece of advice that proved invaluable: if you think that you might ever convert your loft into living space or warm storage, then by far the cheapest time to do it is when you build the house; you can always defer second-fit until when you need the space. So we went for warm-loft and now my adult son who lives with us uses the loft floor as his bed-sit.

That's for the reasons that I discussed. The Q just isn't meaningful as phrased. Very east to ask, but you are expecting a lot of time and effort from other members, and any answers taken out of context will be useless. Your design / construction and heating approach can impact your ASHP bills by a range of 5-8x. It's a bit like asking: what is the average MPG for a vehicle; well it all depends on the type of vehicle: bike, motor bike, eBike, Tesla, conventional compact ICE, Diesel, gas guzzler, ... IMO, you really need to do your own research instead of expecting members to give you lots of detail on meaning of life Qs.

@SBMS, this is really a "how long is a piece of string" type of survey. I don't think that it's going to help you very much at all. Why? The heat demand is nothing to do with the heating technology and everything to do with the thermal design and actual performance of your build. So you need to start there, with the trade-offs between cost, design and construction risk and performance. We have a very airtight, passive-class build with decent MVHR; just UFH in the floor slab, and no other heating for the two upper floors, apart from a couple of small oil filled electrical rads that my HA system turns on for a few hours each night in the worst 3 winter months. I don't even have an ASHP because I can't make a payback case based on my (electric resistance heating for my water UFH loop) energy bills. Next if you use electric heating for your DHW (SunAmps, cold-fill DW and WM), then you can get away will running your ASHP at something like 30°C output temp and you should get a CoP of 4-5. If you use conventional rads then you will need an output temp nearer 60°C and then you'd be luck to get a CoP of 2½. Just because Dave used 1 mW electricity doesn't mean you will achieve something similar 2× better or 4× worse. My suggestion about not bothering about ASHP to heat your water has been covered on other topics. If you heat your water using E7 rates and use some highly insulated PCM-based system such as SumAmp and a HEP20 manifold system, than parasitic the heat losses are so minimal that you really don't spend that much heating your water using electric resistance elements -- certainly not enough to merit investment in more complex DHW solutions.

Anywhere where you think that you might need to put a screw in the floor.

My electrician used a plastic enclosure. I would have been a lot more comfortable with a steel one. ☹️

First I misread the Siemens datasheet. The input will accept 240V at a current draw of around 15mA so yes, this could be switched by the Pro SM4. The advantage of a Wifi based switch is that it removes the RPi from the scope of the inspectors review, though you should have the CE DoC to hand. The disadvantage of Wifi is that it doesn't work too well in a steel equipment enclosure. 🙃 Though you could try putting the RPi inside the enclosure as well In the UK, the rule are different. Your electrics have to be signed off by a Part P certified electrician who certifies the house registration and does this in an online registry so the Binsp (and insurance companies) can look this up. Once my electrician read the datasheet for the Crydoms he was happy to ignore the 5V control signals as these are outside the scope of the certification.

As it happens the answer is the same on both: you can manually set the post date and time on both, with the default as "now". Posts are listed in date order of the post date and time. You can edit any historic post and change its contents. In fact (again on both) you can hide a blog post. I do this when I am in the composing / proof reading cycle and I only publish it when I think it is good enough to be readable. If you look at my early blog posts, you will see that they pre-date the foundation of the forum. This is because I scraped the content of my posts from eBuild and set the DTS to be the original. @Rishard Sorry about this diversion, but that is what we old farts tend to do. You have to take the rough with the smooth. 🤣

@ProDave, Your blog is a Wordpress site so you can just paste in Rich text content into the standard editor or if your posts are in Word format there are a range of add-ins which will be decent conversion for you.