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@Beelbeebub A wiring diagram would be most interesting if you can find it, although I am sure I can work it out.

Deployed ! Loads of issues with the 3d printed case . I’ll rethink that .

I'll try and dig out my wiring diagram but here's the box Incoming tails from grid come in, the SPD and it's breaker are connected there. The love and neutral the head via the SolaX RCD and the live via the MCB out to the solax. They also go into the "grid" input of each changeover switch. The output of each changeover switch then goes to each CU. The eps love and neutral come back from the unit and connect to tge other input of the changeover switch (the live via the eps breaker) Currently CU2 is connected to the grid, the inverter can power it but it will go down in the event of a power cut. CU1 is fed via the EPS and stays up in the event of a power cut. (not shown are some Henley blocks below to split the connections)

I guessed 😄, congrats on your new grandchild.

So elaborate! Not exactly correct - the heating demand rate if 10W per m² max demand is a good indicator that us incorrect. That number being chosen for a specific reason - a heating element in the MVHR (flowing at passivhaus flow rates) can supply that heat without getting a burning dust smell from the ventilation air. A passivhaus still needs heat not much, but some, you don't need a huge gas or oil boiler though.

Don't know what it was made from, but they were little honey coloured granules/balls. I liked the smell when I was a kid.

She's right. Passive stack ventilation is driven by the difference between indoor and outdoor temperatures. In winter that difference is big so it tends to over-ventilate; in theory you could devise controls to restrict that but it wouldn't be easy. On a hot summer day the indoor-outdoor difference can be small, resulting in very little stack effect, so very little ventilation. In fact the outside temperature may exceed the internal temperature, causing the stack to operate in reverse and draw in warmer air from the top down. MVHR is a more reliable choice and offers multiple other benefits as discussed in other threads.

Always a worry when Governments mandate a solution. You'd hope they would learn from past mistakes... Building regs should set standards and highlight agreed solutions, but not prohibit alternatives measures where effectiveness can be evidenced. As to MVHR, I prefer long term ruggedness over perfection. Currently our house is manually ventilated and we have dumb window vents. CO2 is not an issue but moisture can be. I'll add the new moisture sensitive vents and ridge vents just as soon as I finish all the other building works. Only been at it for 12 years so far... @SimonD how did calculate your ventilation and sorbative insulation efectiveness?

Thats a really good point! Thanks. Need to think about this. Any thoughts on NBG requirements for self/custom build. What is really required to be accepted as exempt and what other requirements in that respect I might need to demonstrate. Or am I over-thinking it.

Sure, you can choose to heat a Passihaus however you like without restriction. Perhaps because of that, many people in the UK seem to be unaware of the underlying principle behind why 15 kWh/m²/year was chosen (for European climates) - it's not a random number - and think that they need to pay for a conventional heating system in addition to all the other costs of achieving the standard, rather than offsetting the cost saving. Indeed it's so fundamental that it's the reason that the word 'passive' is in the name - it doesn't require traditional 'active' heating or cooling, because it can maintain a comfortable temperature largely through passive means. It's pretty useful to know on a thread discussing costs vs benefits. Worth mentioning too the innovative use of Willis Heaters as a low-cost heat source for those who do choose to add UFCH; there are multiple threads on the topic.

ITV Tonight Investigation - Floods: New Build Nightmares:- https://www.itv.com/watch/tonight/1a2803/1a2803a9449 Flooding prompts discovery of planning breaches on ten new-build estates across country:- https://www.itv.com/news/tyne-tees/2026-02-12/flooding-prompts-discovery-of-planning-breaches-on-ten-new-build-estates

In Scotland mechanical ventilation become mandatory when airtightness gets better than 5m3/m2. So with a decent airtightness I would worry (like the other half) about piss poor ventilation. For the sake of a small cost in running install dMEV fans or a MEV system

I'd be interested in how this complies with building regs minimum extraction rates etc or if you supplement with extract fans? It also looks very humidity focused, MVHR seems like it'll do a better job of reducing CO2 levels.

Sounds like a good plan. Baby pram is for grandchild no. 4, not for me in my 60's 🙂

So how does that work, if they are helping balance demand are they sucking energy out of the battery or is just by being installed its assumed that house demand will be next to zero in peak times? Without PV you generally as a residential customer, get nil for exports, unless on a one-off scheme for say a Tesla battery

I planned my house upgrades around using the Glidevale I-PSV system, combined with natural internal insulations for humidity buffering. (Windows ready for inteligent trickle vents, undercut doors, and additinal vents between rooms and a central starircase / stack to ridge ventilation). Benefits - zero power use, nothing to go wrong, and zero maintenance. Occupants are the 'smart' part of the system and we are perfectly capable of sailing the ship as required But now my other half is insisting on an MVHR as she 'doesn't believe' passive stack will work...

@LSB >>> looking at baby prams Congrats :). We have the 21 degrees guy calling in at our home address i.e. IP6 late afternoon, so would be pushed to make 5pm. Agree that seeing it in the light would be better than stumbling around in the dark😄. Shall we all make a date for say Thurs March 19th? Sunset is about 6pm then apparently. Happy to host a plot visit - might be marginally more interesting as by then we should have the structure of our walls 'watertight'.

Apparently they're subsidised by the grid for helping balance demand which may help explain the pricing. I'd work on the assumption you may have to buy out of the contract (and get a cost for that, it'll probably be more than the subscription) if you want to sell - says the contract can be transferred, but similar leasing of the solar panels themselves has caused problems for plenty of people when selling.

They aren't. Dovista own the likes of Slovaktual, Weru, Rationel, Velfac and others https://dovista.com/dovista-brands/

The total cost seems slightly cheaper than I have been able to find independently. Money is tight at the moment, so the cost of financing a battery install makes it even more expensive. Absolutely. Which I why I'm sceptical of this scheme, surely there must be a con somewhere.

@Gus Potter Thanks for the screen shots... really appreciate it We've already got some labour costs in the spreadsheet, mostly because we're aiming for supply & fit for the big ticket items (for VAT reasons... 5% on supply & fit, 20% on supply only). Thankfully, labour rates here are not too outrageous if you choose wisely Once it's watertight, we're in no huge rush and looking forward to doing as much as possible ourselves... we've done it before, albeit on a smaller scale, and while we're admittedly getting older, being hands-on is one of the drivers for the project. This is bang on... There are quite a few aspects of our plan that many would question, but we are determined to have... a few economies elsewhere make the justification a bit easier

Ok thats great to hear (not sure you said that before) and thanks for highlighting this. It's revealed to me my sloppy language, I'm sorry for that. When I said 'it's wrong' I was mainly referring to the system only being on 4 hours a day. I think it needs to be on longer so you have more warmth. I'm not proposing lowering the radiator temp in the short term. In the long term (after you've made some more improvements to your property and you've been able to maintain a better temperature) it would be good to look again at the temperature of the radiators. Once the room is warm, you won't need to feel the heat from the radiators any more to feel comfortable and then you can start tuning for efficiency. Modern heatpumps can support a property like yours. It's a myth they can't. It's possible the one you have is a bit too small and it seems likely that you need to make a few more improvements to get it working in your situation but it's very much doable with a little thought and care. @Dillsue has highlighted similar examples. If it's colder inside than it is outside, are you opening the windows to try and get some warmer air from the outside? (not during your bath but before and definitely after to clear the moisture) The problem you have is that your building has a lot of heavy solid materials in the structure. These take a long time to heat up and cool down. The key to living comfortably with them is to stop them cooling down in the first place as trying to warm them up quickly will lead nowhere. Clearly your bathroom has got cold and once cold a towel rail isn't going to be able to compete with the raditors emitting cold that are the walls. As a temporary measure while you explore the improvements already discussed, it might be worth considering abandoning trying to heat the space and focus on just heating you. A good way to do this is radiative (infrared) heating panels. One of those pointed directly at you while sitting in the sitting room will likely make you feel a lot warmer and use less energy than running the heatpump. Not so good for making you feel a bit warm when you get up in the morning, but maybe an idea for evenings. https://www.toolstation.com/tristar-smart-infrared-panel-heater/p78401 (not a recommendation just an example) Still, I think you can do better than just heating yourself if you can prepare well this summer.

If alan can't make 5pm them we could meet later somewhere else. I'm pretty free today apart from looking at baby prams 🙂 at lunchtime

£35 x 12 x 10 is £4200 so doesn't much in the scheme of things Web site says "Midway through the contract, you’ll have a choice: either continue with the monthly payments or pay a settlement fee based on the contract’s remaining value at that point" so it may be an expensive option? Only thoughts are - do they have the ability to suck your battery dry, at any time they want, so they get paid for export and you pay to charge the battery? Things that sound too good to true, normally are

Let me know if I can help @fatgus drop me a message if you would like to.