JohnMo

Why? You will always get less heat recovery!

You should have structural drawings from roof supplier or approved ones by your structural engineer. If you have neither get them done ASHP. Nothing so far mentioned wind loading, roof overhang etc

Are you sure? Residential building are 7.5% while roads are 11.8%

Every time the boiler starts and stops. Short cycle time affects gas consumption in a bad way. So an on/running time of about 6 mins or less isn't good. Cannot answer that, you would have to try and see what happens.

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.