JohnMo

DucoBox for MEV looks good so does Passivent https://www.passivent.com/product/intelligent-mechanical-extract-ventilation-system-imev/

UFH and condensation isn't an issue, as long as you control flow temperature. You manage the dew point inside the house envelope (what it's doing outside that envelope doesn't matter). But the way UFH cooling seems to work on the person is floor is cooler and pulls heat from the body, so actually room temperature feels cooler than it actually is. On the room temperature it pulls heat to the colder floor zone. Adding ceiling (or wall if easier) cooling into the mix should work well as cold air would continually fall.

Doesn't that drive you to a thermal store? Especially when coupled with an oil boiler? The thermal store provides mixed down water to the UFH and a plate exchanger the DHW. I would miss out the Nilans unit altogether, bucket load of cost, that really adds no value. So airtightness - are you aiming sub 3 m³/m² @ 50Pa score, if not don't waste your money on MVHR it will actually add to the heating costs. A MEV or dMEV setup to be humidity controlled with matching humidity activated trickle vents would be away better option. Just keep the heating/DHW simple and do not combine with a ventilation unit.

A hand saw and about 5 mins of work? A plunge saw or jigsaw with width gauge or a straight edge clamped in the correct place to give a final cut width required, a couple of mins and 30 mins finding everything you need. Finding somewhere to do it, then travelling there and back? Suspect way longer.

MVHR is unlikely to help that much, flow rates are just to low. But warm air is lighter so will rise via any open spaces. Have you thought about bedroom cooling?

I have a fancy back lit mirror. What a waste of money, apart from using once or twice the first week, don't think anyone has ever switched it on. Used as a mirror full stop. Music while an electric toothbrush brush is your gob or your in the shower, why?

China mostly - they supply tools dirt cheap, so most things can be done DIY, so little or no call for a man to it for you.

To give you feel, we are single storey very poor form factor, loads of glazing, MVHR etc. 192m² at -9 we have a heat loss of 3.2kW. That is using Jeremy's spreadsheet and tested with a heat meter to be correct. We have a 6kW heat pump, but due to it being a range rated larger heat modulation isn't the best, but does a good enough job. If you are set on an Ecodan, don't do the 8.5kW, do the 8kW. The 8kW has two heat pump compressors in series. A fixed output 2kW and an inverter compressor at 6kW. So modulation galore and a more flexible offering.

I am using a Harlequin 6. No issues. Only real bugbear about most the units is the air compressor, it uses quite a bit of electricity over the year.

Time for a revisit. Look at costs of running etc Are there cost savings to be made by having a hybrid system. Short answer is NO. It cost more than a £100 to have the boiler as well as ASHP per year. Gas standing charge is 29.5p daily or £107 per year. Gas used over the last 12 months 469m³. Typical calc for me to kWh 469 × 1.02264 × 38.0 ÷ 3.6 = 5000kWh. So total cost of gas 107 + (5000x5.38p) = £376. To displace the gas used assuming 95% efficiency 4750kWh of heat from ASHP. So boiler generally used at close to zero or below, so will assume an average CoP of 3. 4750 / 3 = 1583kWh of electric. Currently I pay 13p for 7 hours and 30p for the rest, but have a 13kWh battery. So will assume 70% of all electric is 13p the rest is 30p and ignore solar inputs. 1583 x 70% = 1100 @ 13p is £143 483 x 30p is £145 So total cost for ASHP running instead of gas boiler £288. £376 - 288 is £98. Plus additional electric to run a circulation pump and boiler control, that is not needed any more, without the boiler. Additional savings can be made with ASHP, running at higher set point with excess solar. Run at elevated flow temp during cheap tariff periods to mitigate running during expensive periods. Move to a different tariff, so battery charge is done during day also. So suspect a further £50 to £100 saving per year could be possible, by using nearly no expensive period electric. So have now requested gas meter is removed, to stop standing charge, have fully electric isolated boiler.

Assume you actually mean 28kWp? Your solar and batteries and time of use tariff will drive the cost per kWh of heat down to almost nothing. If you are paid for export would expect to see you paying almost nothing for electric, which will include all your heat now. Lpg would always be in addition to electric so always a cost adder.

Your torque tighten, to ensure the bolt is stretched and is ideally mid way in the elastic range of the bolt or stud. This allows for changes of temperature, vibration etc and the bolt to maintain tightness of the assembly. If you under torque the bolt is not in the elastic range of the bolt material and if subjected to cyclic fatigue will give a very early failure of the bolt. It will break. If you over torque the bolt goes out of the electric range of the bolt and will stretch the bolt permanently, the bolt will yield. At this point you are applying almost no clamping force with the bolt. Your correct tightening torque changes due Bolt minimum dia Bolt coating Threads being lubricated Grade of bolt - 4.8, 8.8, 10.9 etc So you have dissimilar materials, aluminium and steel. You hot dip galvanise the steel structure, but be aware a strong galvanic corrosion can occur especially when wet between aluminium and zinc (galvanizing). If the top of the screw piles are steel no issue, if they are aluminium - ideally you need an insulated bolt kit, this will sleeve the flange holes and below washers, the flanges would need to have gaskets as well.

I would dump the 90 x 25 batten and add another 90 x 90, bring the floor insulation up to 200mm. Then 70mm screed. Insulation mineral wool

To have no emitters upstairs your downstairs UFH has to output enough heat to satisfy the whole heat house load. The other thing is the assessor may have taken MCS default air changes and a bunch of other default numbers. So it's sh!te in, sh!te out heat loss wise. That sounds worrying. It should be sized generally for the heat load. Which may indicate the issue in the second paragraph sh!te in... Look for another installer. Or don't bother with the grant. Go and get a Panasonic, Hitachi etc heat pump from internet or local wholesalers.

They generally run circulation pump at a fixed speed and speed is adjustable via the controller. Believe they actually run on a moving dT to ensure long cycle time, but with a fixed (user/installer adjustable) pump speed. So maybe the pump.is just running way to fast and hence the noise.

I was referring to the only pump in the system with an ASHP. They don't have additional pumps required for a gshp. It also outside, not inside. There is zero noise inside. So plenty of noise

Only pump for heating is in the ASHP itself, so manifold for UFH is total silent. Wife was stood by ASHP doing cooling today, unaware it was even on.

To add to what @JamesPa says our new build (started in 2020) was originally gas. In 2023 we put in an ASHP. Messed about with hybrid and have now asked for the gas meter to be removed. Having gas meter standing charges are £110. Saving made running gas over ASHP near zero and below about £20 per year. Gas is costing me money (£90).

Other thing I forgot to say - new build fit UFH - it's a no brainer. If a single storey it's easy. If a two storey size the UFH circuit to supply enough heat for the whole house heat loss. Then you need no heaters in bedrooms or fit fan coils in bedrooms for heat and cool and size UFH for just ground floor. Then choose an ASHP that does cooling and use floor as a cooler. Ours has been on cooling mode since April. No condensation house temp nice and stable. 26 today, house at 21-22.

The recirculated cooker hood we have has worked well. It's is very often off and not needed with continuous background ventilation. We have MVHR, but the dMEV fan would perform the same job. If you go this route get a Greenwood CV2 or CV3. There are really very quiet and easy to set up and will boost automatically based on rising humidity. Generally pretty cheap on eBay.

Think OP decided the criteria, not AI

I did most. Roof no (all internal battens yes), electrics no, plasterboard no, ground works no (except insulation and UFH) but did just about every thing else. I selected my battles

Sorry architect is talking utter rubbish. A simple design ASHP (so no zones, no buffer) will do anything asked of it, if sized correctly. You basically run it 24/7 on the lowest acceptable flow rate to keep house temp stable via weather compensation. Ideally size rads to a max design flow temperature of 45 or below. The lower the better. The exact same rules above apply to a gshp. Sub 5 degs outside the gshp will get a slightly better CoP generally, but the average winter temperature is generally higher than that. At warmer temps the ASHP will get a better CoP. Any savings aren't worth the additional costs of installing a gshp.

That looks like it may hurt a bit.

Why not keep it sorted of simple. Recirculating cooker hood, then a dMEV in an appropriate easy to install place.