JohnMo

I just used 70mm PIR upstands on all external walls.

But your only moving the heat a degree or so either direction. No different to an overnight setback, then adding the temp back in a couple of stages, which allows the heat pump to gently heat the house up. Which is pretty much what heat geek and others and your general common sense says is the right thing to do for the best CoP. Basically slow and gently does it. The OP hasn't or isn't doing that, he has most of the house heating off, which doesn't let the heat pump flow at the correct rate, and the rooms he is trying to heat, cannot heat up well because the heat is moving to anywhere colder in or outside the house. Those two things on there own will give a rubbish CoP.

Me also, wife wasn't keen

Would work, but Something like this would be much better or something from Duco or passivent https://www.ventilationland.co.uk/product/44535/itho-daalderop-cve-s-s-co2-optima-inside-package-hp-415-m-h-plus-build-in-rv-humidity-sensor-and-co2-sensor-plus-4-ventilation-valves-plus-auto-rf-control-perilex-plug.html Then you just demand controlled inlet and you are good to go.

Are you just reading my first reply and rewriting it?

You don't have to have trickle vents, things like this are also available from various manufacturers https://www.aereco.co.uk/products/air-inlets-uk/eht/ https://www.bpdstore.co.uk/glidevale-energy-saver-humidity-sensitive-trickle-ventilator/p/182

dMEV are silent also, not the same as a normal bathroom fan. A few watts to run each.

MEV and dMEV run 24/7, so not sure you need a shutter. Do the same in the kitchen and cooker hood set up to recycle.

Look into humidity controlled MEV and dMEV. Basically the trickle vent will open and close as required and the fans like wise. Overall a lower running cost compared to MVHR, no filters, and good energy conservation. Some bedtime reading. Atamate_SDAR+Paper+2019+(1).pdf

I just used a small saw blade in a Stanley knife blade handle. Foam filled any gaps

Our flattish roofs 12degs. EPDM/PVC with fleece below, 18mm ply, posi rafter 256mm deep. Underdraw with 2x counter 50mm battens, full filled with spray foam insulation. Then vapour control airtight membrane and a further 50mm counter batten and then 12.5mm plasterboard. Rain is a soft patter not intrusive, strangely you can hear grows on the roof but nothing else.

GSHP slightly higher CoP, but may not have at the tale end of winter, if you have cooled the ground too much. Not always inverter driven, so may not modulate as much, so will need a buffer. Generally a big faff, with digging and slinky and filling, ASHP easy to install.

Couple of things going on. A cylinder with a coil is designed to have around 75 degree flow temp going into it. As you reduce the flow temp the heat exchanger coil cannot transfer the heat away very well. When you get a certain point in the heating cycle the boiler will trip on a high return temp. Then go in to short cycling. As you are seeing. Not efficient. You may use less gas by ramping up the flow temp to 75, your return should be around 55. The heat cycle should be quite quick.

My wife makes a broth soup full of lentils and pearl barley, that's all you need and a hose pipe. So come around for some soup, wait about six hours, all the biogas you will ever need.

You can get a batch mixer, it has an auger in it for mixing and pumping out. Seen that done. But takes an age, if you are DIY ok, but paying someone, big cheque book required

Only things I would say about the cylinder is it insulation is very thin, so make sure any heat loss is usable. If you intend heating the cylinder to use on the overnight electric the buffer would be better on the supply side of the system. Is your heating system pressurised, if so the cylinder will need to be pressurised also with the same protection.

Daft question, why would the UFH pipes be anywhere near where the walls are going to be?

Without a pump is really a non starter, we did a couple of small sections of wall between windows and took ages, we used buckets, there is lots of concrete in the walls. I would start looking for a different build method, if it was me.

No issue with a buffer on the return leg. If your using electric to do heating and not oil, but confused with this bit and relevance to oil and a buffer? Easier fix to balance the heating system so that all circuits are on and flow at the correct rate for the room heat transfer required. Then no buffer needed. Sounds like you have too many thermostats.

Sorry but dream on, your downwards heat loss makes, UFH less than efficient. Slightly oversized rads to run at a lower temperature would be more efficient, as the downwards heat loss is lower. Your boiler would operate in the same region as it would with UFH so it's efficiency would be the same. Bury the pipes in the wall they are gone. As you say it your choice, your money. But seems a lot of work for higher energy bills for ever more.

It's great getting all these prices, but where is the structural design. If the structural engineer says no your back to square one.

Is high end just something that's been given thought and isn't just the normal monopoly house, with the basic fitted kitchen and bathrooms. High end can mean nothing, it maybe just saying you spent loads on finishes, lights, floor, kitchen and bathrooms, doesn't mean it looks nice, functions well. In our pavilion (bungalow yesterday), we have a great kitchen and great bathrooms. We spend quite a bit of time on the design, then sourced the right quality at the right price. You don't have to spend a fortune to get a high end finish, but you can. If you entrust the buying and design to a third party you will pay a high price for you high end finish. As with all things self build, if you truly self build you are very much in the day to day driving seat, if you self build by getting a third party to do everything for you, you are a passenger who pays the fees.

Yes

This is why you have to balance the system, it doesn't know the temp

You can get bends and plenums which give you direction changes. Your boost only needs to be 25% above normal flow. Your normal flow is between 0.3-05 ACH. So work out you ventilated area of the house and divide by 2 to 3 to get your overall flow rate. The extract and supply should be equal and be at the rate you calculate. Put a manual boost switch in kitchen and outside bathrooms.