Wumpus

This is the key. You will likely do well in heating season, through the winter, but does this hold out in the summer, when presumably your heat pump is working a lot less hard? You can shift some/most hot water to off-peak tariffs anyway, so perhaps not so much saved there? I suggest looking at how your electricity demand varies month by month and see how many months of the year you would get 13.5kWh of benefits. That might extend your payback calculation a lot?

This sounds great. Can you recommend the company?

This could be tricky, the bigger return on investment is on DHW. Our UFH flow temperature is 35 degrees, but that wouldn’t make a dent in the hot water?

I like this idea. I would need my plumber back as I certainly don’t trust my abilities in that direction, but the rest is very possible. There is intello fabric on the wall where our MVHR ducting exits, so I guess just adjacent to that and good taping to keep everything airtight. Thanks

Fair challenge and this may be the path we go for. I was trying to reduce our CO2 footprint and perhaps enhance value if we sell in the future. Of course we could remortgage as well.

Hello Buildhub, I need your experience please. Theres a bit of a story to go with this, so bear with me. We completed our house last year and have been living here for over 18 months. The house is built to Passivhaus principles - air tightness tested at 0.38, insulation is great with floor 0.09, roof 0.1 and walls 0.13. Triple glazed throughout (Norrsken, very happy), MVHR at 86%, thermal bridges minimised. We did not complete a PHPP but do have detailed heat loss calculations for each room. As funds got a bit tight, we didn’t put in the ASHP we planned, and instead put in an electric flow boiler which feeds our lower floor UFH, and we have a direct electric cylinder. Maybe this was a mistake, no point go in back over it. The house is performing exceptionally well. We batch heat the lower floor slab overnight in Intelligent Octopus GO hours, and typically the requirement is 10-15kWh a day. We don’t really top it up during the day except when very cold outside, which is not very often in Devon. The internal temperature loss is around 1 to 1.5 degrees a day and we maintain the lower floor between 20 and 22 degrees (heat to 21.5 overnight). All of our heat for the last 12 months (2600 kWh) cost us £191, which I think is pretty good. Hot water (4100 kWh) about £340 a year, again overnight. All this points to an ASHP being of marginal value, we won’t save much on £530 a year and need to add in annual servicing. At a COP of 3, we might save £350 a year on the electricity? This would all be “case closed” if it were not for our mortgage, which is with Ecology (who are fantastic). Ecology offer a discount for achieving a B or higher SAP on the as-built building. Our SAP as designed was A101, our as-built is C79. The only difference is the change from ASHP to electric boiler, everything on the SAP certificate is “very good” except for heating and hot water, which are “very poor”. Our insulation levels exceed the as-designed SAP numbers. We could spend some time discussing how SAP does not do a great job for houses like ours, but again not much value here. So, I had an MCS certified contractor around to look at replacing the electric boiler. He pretty much understood that we have a house with very low heat loss, but old me that he had to install heat emitters in every habitable room. We don’t have UFH or radiators on the upper floor, and adding them would add a lot of cost and make quite a mess of the house. Any advice or experience from anyone on whether it’s is an MCS requirement to have heat emitters in every room, or any other thoughts on how to proceed? The mortgage discount is worth doing if the costs are less than £2500 including the government grant. Thanks all

We used compacfoam to form the upstand. Robust and insulated.

It might be possible to create a couple of terraces and use the dig-out from the lower level to backfill the upper level behind some kind of gravity structure like gabions. Cartaway will be expensive so best avoided, especially as your access looks difficult. It will need some kind of excavator I would think, not something you would want to do by hand. another option might be a criblock system which can look softer than gabions.

I think this will be more of a building control question rather than planning. There are rules about how close to a building the treatment plant can be, from memory more than 15m. I think planning is only concerned with demonstrating a viable scheme, so once that is achieved, any alternative location would work. Any scheme would need to be approved by your building control officer, so I would start there. I’m pretty sure you could substitute for any alternative treatment plant. A lot of people dislike the bio disc units because of the moving parts and greater mechanical complexity.

Yes, potentially helpful for a PV installation. You would be allowed 16amps export on each phase, if you can get that much on your roof, without requiring special permission from the DNO, so more than 10kWp. If you install your PV on a single phase, any exports net off against any imports on the other 2 phases at the time. Same standing charges etc. as single phase.

Agree it would be better to deal with the water behind the wall than try to hide it. Is it too late to put in a land drain behind? Some form of waterproofing membrane on the back face would give the best result.

Costs may not be as much as you think, it would be worth getting a quote from the DNO, but as you say, it may depend on available capacity on the line you’re connected to. Off-peak tariffs are available on 3-phase. We have Octopus Go on our 3-phase supply and it all works as expected, the meter just adds together the 3 lines to give a total kWh consumed.

Just my take, without understanding how it looks from the outside, but I would centre all three on the same line - front door, French doors and glazed doors? Centre on the dining room/table so you can see through the side windows front to back.

Bit slow to respond on this. I did my own KNX installation, along with our electrician who ran the bus cables and radial 240v cabling to two KNX cabinets. It’s all very possible and is absolutely solid. No complaints at all, everything works as it should every time. If you have questions let me know. ETS takes some getting used to, but once you get the concepts it is all very logical.

If it’s any help at all, our contractors use about 10kWh per day for everything, including the site office heating, kettle, power for tools etc. They are pretty good about switching stuff off when not in use and I am OK to pay for it. This is for a team of 2-6 depending on the day. It was a lot less in the summer of course.

I have to endorse the comments on wet underfloor pipes. We have a Passive build and our contractor suggested we wouldn’t need much heat and panel heaters would do the trick. I am so pleased we initiated on underfloor heating pipes. Experience has shown that 3 hours overnight on Octopus Go tarring does everything we need for the next 24 hours. We put in an inexpensive electric flow boiler rather than Willis, but the idea is the same (long story about our plumber not really liking the Willis and this was a compromise). The savings with a heat pump didn’t add up for us, we spend about £1 a night on heating and with a COP of 3 that would save 66p a day which takes a super long time to recover the costs of a heat pump. We can add one later if needed. The concrete acts as a great heat store and I don’t think we would have got there just heating the air.

Always learning. We bought the Mixergy and are happy, but I like to understand alternatives if we ever do another build (not for a while, we still have the scars)… I get how the overnight can work well with our 4 hours of Octopus Go, but less clear how the day works? We use a “maintain at max 20%” strategy on the Mixergy, which uses a small amount of daytime power. If we don’t top up, we run out for washing up and hands in bathrooms etc., but it uses very little electricity to get to 20%. How does that work with a twin immersion strategy? Genuine question, looking to understand. thanks

I really like our 300l Mixergy tank, it has many positives. We heat overnight to 80% and then maintain at 20% for the rest of the day after showers first thing. Just be aware that it’s quite slow to heat on direct electric at 3Kw. 4 hours overnight takes ours from 20% to 80%. Although what is produced is available quickly, large volumes of hot water take time. The max temperature is 65 degrees. it works for us, but it’s not anything like instant.

I have a couple of thoughts, and I hope they come over the right way. First, undertaking any project like this is hard so do cut yourself some slack. It’s a long slog and will be a lot easier with a trusted contractor, but mistakes happen on all sides. It sounds like he’s well intentioned, and that is worth a lot. Second thought is that you can’t be on site every day, so you need him to care about the details as if it were his own house. Getting to good airtightness takes a lot of attention, minimising thermal bridges does not happen by accident and if he’s not checking the subbies and there every day, how can he be confident you will get the results you need? The electric bill seems to be a small symptom of a bigger oversight question?

Fair point. If the oversight isn’t enough things will get missed that are more significant and in a Passive construction that’s not going to be a good thing. Would a “disappointed not angry” approach work? The suggestion to add a timer might work? …or if they really don’t care they will override it somehow?

…to add, I think this is the key point. A good working relationship with someone you trust is worth an awful lot more than some electricity?

I would expect them to be reasonable and not leave the heater on when they are not in the site office. I don’t think there’s anything wrong with pointing out that it’s a lot of money, or possibly that it’s a waste of resources and the environmental cost is poor. Ultimately I think it’s your cost though. I had similar irritations, but I do not begrudge the team having a place to warm up and dry off. The winds and rain in Devon and Cornwall are more than a bit persistent after all. I do get a bit irritated when the doors of the house are wide open and there’s a fan heater blasting out, but usually just swallow it. We were running at around £200 a month for electricity over the winter for contractor use. It will drop substantially when the weather gets warmer, which hopefully is soon. Perhaps just swallow the costs until spring?

I have had 2 Miele washing machines and would not have anything else. They last for 20+ years and are super quiet. They do weigh in at the heavy end of the scale. We moved ours into the new house and it nearly didn’t happen because of the weight. if you shop around, John Lewis often give 10 year warranties, which gives some reassurance, although I have never had one go wrong (famous last words). I think it’s worth the extra cost for the longer lifespan and warranty.

Ours was finished with ply sarking and Tyvec over, then battens etc. The sarking is mechanically fixed to the insulation with plastic fixings to minimise thermal bridging.

We have a similar condition, building in an AONB. We discharged it by submitting details of the light fittings to be used, and yes, all pointed downwards. I think they also look for nothing too dazzling. We also had a condition to have them on a sensor (but interesting there is no comment on how long the timer can be)