JohnMo

Sorry this is incorrect. The MVHR in and out flows, are balanced - same is taken out as brought in, so house is neither pressurised or depressurised by MVHR. MVHR also slowly decreases house temp (assuming colder outside) as the efficiency of the heat exchanger within the MVHR unit will never be 100%. Ventilation heat loss will be based on approximately 10 to 20% of the overall flow rate of the MVHR unit, plus natural ventilation heat losses based on house airtightness. So airtight house, ventilation losses are almost all losses produced by MVHR, leaky house plus MVHR, are MVHR losses plus natural air leakage losses.

Are you room warm enough is your boiler running without too much cycling? dT is all to do with flow rate, if you moving too much water through the system dT will be low. You could turn down your circulation pump. But if circulation pump speed is controlled by boiler then the boiler is happy with the dT so don't mess with it.

In theory it may be ok, but heat loss is best guess, and the -2 is unlikely to stay constant all day, so could be correct, but may not be. At that temp outside you could have a bunch of defrosting happening also to confuse things.

Things flex so they don't break. Our 3G windows flex, think at full design load our 2m tall windows are allowed to flex many millimetres - according to the structural calculations.

Shouldn't really have said effective, should have said efficient. Pump enough heat into anything it can be effective. Downwards heat loss also means more heat is always pumped into UFH than radiators - insulation depth make it cheaper than it would otherwise be to run. You can have a lower flow temperature also.

You are trying to make the system resistance similar everywhere. So if some parts are not getting enough flow, you have to increase resistance elsewhere, by closing the LS a little.

No chance of that here. I get life is for living, 'stop going on!'

My 6kW ASHP (R32) states min 3,95 / nominal 6,08 / Max 6,99 As demonstrated above min output is coincidentally with max demand i.e. at lowest outside temp. I need house heating on, at about 10 to 12 degrees outside, which when looking at the performance chart ASHP is make about 6.7kW at 25 - 30 Deg flow temp. While at -10 its max output is closer to 5.7kW. So I am looking at nearer 40 to 50% turndown in reality. So my 6kW at minimal demand is making closer to 4 to 4.5kW at minimum demand temperature.

Many a similar conversation during and after our build. One said that I would green mould on the walls within a week of moving in. No joined up thinking or understanding you could actually have a ventilation strategy, had never heard of MVHR, dMEV, would only ever install intermittent fans - why anything else?

Smart and simple

Measured heat output or calculated for flow/return temp and actual flow rate. All electrical energy use - timer, controllers, all pump, immersions etc. Divide heat out by electric in.

They can if you give them an air test certificate. They don't unless you provide a certificate and insist.

Visibility splay are a roads or highways thing. So they are the people... Remove it, if on you land, just tell them they 24 hrs or you will chop it down. Go to B&Q buy a cheap saw, if you don't have one.

There are advantages for you if the supplier uses a lower design temp of -5 or lower. First if they set the flow temp at 45 for -5, in reality you have a system that will most likely work well at 40(ish) at -3, so get a better CoP. When the heat pump is running at -3 you will be in defrost mode so loosing approx 10% of output, so don't fret too much. All depends where you live for design temp - MCS are wanting the system designed for 99.6% likely lowest temp. For us that would be -9.

Think my boiler is 32kW it's a combi, it modulates to about 6kW, yours will modulate down to about a third of that. You have UFH so a huge buffer to work with, your will happily accept huge kW input. If you have a 19kW heat loss (very much doubt you have, unless you have a wall missing) or half that, your boiler is in a happy enough place. Car analogy, just because you have 200hp does mean you use it, most the time you are using a 10th of that. More importantly, is your boiler stop/starting 100s of times a day? If it only stops/starts a few times a day, happy days.

A few issues 12kW is huge has he actually done heat loss calcs. Ideally with a heat pump you would have everything on or everything off as a huge heat pump needs huge flows. 12kW will need between 28 and 40L/min. Why only a 170L cylinder as heat pump temps that is small there are two of us and we get though a 210L most days. You ideally would need to control through the heat pump controller. You would also dump S or Y plan and install a 3 port diverter. Call for heat is normally controlled by heat pump.

Just had that with my front door, tried to use rechargeable and only getting a couple of weeks out of them. Just bought some lithium AA batteries supposed to last about twice as long as Duracell's

That will hit your CoP big time. Switch that function off completely. Time to heat once or twice per day only. The run time will be longer but the CoP way better. My 6kW and 210L takes about 40 to 50min on a single heat. With a single circulation pump you have to balance between heating and DHW. So you will have to play about to find the right settings.

Min amount is just what is required to support normal defrost cycles. It doesn't address cycle times during normal running. Normal running cycle times are governed by min ASHP turndown, and min house heating load. If your min turn down is 3 kW and house min heating load is 1kW the heat pump will cycle on off to cope. The more water volume you have the longer the cycles.

I have a Greenwood CV2 dMEV fan in a summer house, I had to pull the cover off to see if it was running they make so little noise. Would pull about a 100th of you humidifier electric.

Why not just a Shelly H&T (or similar) in each room, integrate into a min max helper and use a generic thermostat, do it in home assistant. Then bounce the signal about via wifi?

Be careful with the number of zone and their size. Small zone means boiler short cycling. Which in turn results in bigger than expected energy bills. Humidity issues indicate an issue with ventilation, use ventilation to resolve dampness. You only need thermostats with humidity sensing, for cooling, not for heating. I like Computherm thermostats they are not smart but are good and transmit through think concrete walls, and into a foil lined shed without issue. UFH is best left to tick away on a low flow temp.

That fixes humidity, but not the CO2 issue you will have. You NEED ventilation. Your living environment will be bad for your health. Sorry I am going to very blunt - Airtight without ventilation is not a good or smart move. Add a couple of dMEV fans one in kitchen and one in bathroom(s). You then need to allow air in somewhere.

Only do that if you have fixed every draft and been air tested to 3 or better, otherwise that defeats most benefits. If you are reasonably draft free you are better doing dMEV or MEV. Something like Greenwood CV2 or CV3 fans for dMEV and then add self modulating trickle vents. Cost pennies to run, can be bought from eBay super cheap and are just about silent - they only boost when needed and they do that automatically based on humidity. MEV same deal, but you have to run ducts to central unit.

Not enough insulation for UFH to be effective - stick with rads