JohnMo

You just need a robust ventilation strategy, my curtains blow about isn't a ventilation strategy. Don't you need to measure the relative humidity instead of absolute?

You can normally program any heat pump to have either of these properties. But it depends on your system, if one method better than another. I found I got unnecessary frequent starting and short runs with the circulation pump off or in sniffing mode. But makes a big difference if UFH or radiators also. I have UFH and the continued circulation helps the system determine based on return temp when the floor needs more energy adding.

Watch with interest. Did have a multi car policy once, but at renewal it was cheaper to split. Motorbikes seem ok doing it that way, cars and vans?

Not sure that would be the best solution, the floor takes an age to heat up then an age to cool down. So chasing your tail to get the right temp for sleeping. Upstairs if going A2W no need for A2A, just use a fan coil connected to A2W HP. Then you have heat and cool in a single unit. Yep If you keep oil, consider a thermal store, to provide DHW and a buffer for the oil boiler to give a decent run time, especially if you have zoned heating. Pul the CH water direct from buffer. This would be rubbish with a heat pump. You will also need to be careful with the oil boiler short cycling, with lots of zones Good UFH doesn't equal a warm or hot floor, poorly installed does. Well insulated, you are flowing mid to high 20s, maybe low 30s on a very cold day. Would agree. I would step back Decision 1 - keep or dump oil. Once made every thing else starts to fall in to place. Just jump one side or the other, don't keep jumping. UFH downstairs - not the best solution, simple low temp radiator, with a manual TRV to manage room temp. Good for Oil or HP Same upstairs if oil and A2A. Or fan coils for A2W. Thermal store for Oil, HP UVC for A2W HP.

Clip can be purchased from super foil, I didn't bother, as they would fit our fat joists. So just stapled onto the vertical face of each joist. On a big roof the clips would be better and quicker.

I did similar on our garden room, but with 200mm of EPS in top instead of PIR.

I would do the longer runs in Hep20 and the then convert to copper as you come out the wall. Plastic fittings tend to be big and ugly, so keep them in the wall.

Couple of observations Foil insulation works with an air gap either side, so it acts as a reflective membrane. The insulation value other than that is pretty rubbish. Would rethink your way of heating.

As they say it wouldn't do any harm. If you find a crack that's good. Just do it as low temperature as you can

Different flow temperatures give different radiator outputs. Perhaps the one quoting the lowest radiator output runs the system a much lower temperature? If so this is good

The grant is up to £7500. If your install costs £8000, you pay £500, if it cost £15,000, you pay £7500. Cylinder is around £1000, Heat pump £2500, and £500 to £1000 for stuff, if they are not changing the system much, you have a few days of work for the plumber and a day for the electrician. Anything more than that is just profiteering, ripping you and the tax payer off.

The heating isn't going to be cheap to run at that flow temp. So I would expect the installer scope is very limited, would expect the cost to be no more that the grant money really, if the existing heating system isn't being upgraded.

If you want it via a grant MCS DHW sizing apply. So 45L is meaningless. The only important bit missing is design flow temperature. Ideal 35, just about acceptable 45, 50 and above, walk away. 1 zone or loads of zones, buffer etc, what are the details?

I would (did) 200mm PIR, poly sheet 16mm pipes stapled to PIR and though poly sheet and then screed.

You have to very careful mixing strategies as even with the bedroom trickle vents the bedroom may not be properly ventilated as you don't get a draw through from any fans elsewhere. Do you have a basic plan you can post up, there maybe some simple solutions. Also how airtight are you planning if not below 3 for the whole house MVHR may not be right solution for either part of the house

No, there are no trickle vents, it is MVHR, just implemented with minimal ducts

I would make a change take note of electric meter readings, with average daily temperature. Ask as many questions as needed.

You have a start and stop hysterisis for the compressor. So for a target of 25, the return flow will drop by a predetermined amount below the target flow temp, once at that point compressor starts. It will run until the shut off hysterisis temp is reached. How long it runs depends on system volume, heat demand and how deep the heat pump modulates. My settings are based on my system and what it does and doesn't do. Mine at a target flow of 25, start up hysterisis is 5.1, so return temp is allowed to fall to 19.9, before compressor start. Cut off hysterisis is 2.3 so cuts off at 27.3. My total hysterisis is 7.4. All this changes with different heating systems and houses. Mine is 300mm spacing UFH in 100mm concrete screed. Heat pump is a Maxa i32V5. Today excluding DHW the compressor has started 5x times up to 10pm, shortest run time was 18 mins (9 degs OAT) and longest run 2.5 hrs (5 Deg OAT). WC is all about running just enough to top up the energy in the house, so I use the hysterisis and a WC curve to play with the floor heat output. Based on the floor average temperature, to get the correct heat output. The WC curve starts at 15 Deg OAT at 25, this gives a floor minimum temperature of 19.9 (don't want the heating on really at that temperature), at -9 the WC curve stops at 30.3, so floor temp is a minimum of 25.2 (not tested this temp yet). So far this is working fine down to +3 degs. Depending on actual run times at sub zero this will affect where WC stops and at what flow temp. But once set it's set for ever.

Think I saw all the various wiring schemes on the Homely website

Cascade is a system configuration used by people like Fresh-R also a configuration used by Brink. Just as effective as normal MVHR, infact most MVHR is using cascade to a lesser extent. For example lounge is supplied with air, air then moves though the hall and is extracted in the kitchen, the hall is ventilated via cascade.

No more Q's You need to have think about how you actually operate the system. Timed heating slots will drive up your heating cost most likely as the heating system has to run hotter than ideal to play catch-up. more further down I would suspect you have two control methods in each room - a radiator thermostatic valve, so this controls the radiator output based on room temp, plus what sounds like a room thermostat that possibly calls for heat from the heat pump. Your UFH will also be calling for heat randomly, so the whole system is likely to run rubbish and cost huge amounts to run. My advise Bedroom wall thermostats set very high so they are unlikely to stop calling for heat. Set radiator valves fully open for now. Set all UFH thermostats high, so they always call for heat. Remove all timers and set to run 24/7 Now you need to get access to your heat loss calculations and the weather compensation setting in you controller. Read your manual At the warm weather end of the WC curve, set to 25 deg flow at 20 degs outside, the cold end set per your heat loss calculations, so design outside temp to max flow temp. If you have predefined curves to select check and adjust as required. Now you need to adjust the WC curves to get the lowest flow temp and a stable comfortable house temp. Now adjust your bedroom radiator valves to get a comfortable bedroom temp. This will take a few days at least. You are now at the cheapest running mode, then adjust slightly to get the comforts you need. Never switch off, just have small 1 to 2 deg setbacks.

MVHR and dMVHR does not need trickle vents. You have to have dMVHR in every room, for it to be sound ventilation strategy, so stupid expensive and you have to meet the minimum whole house flow rates. Have to you considered cascade MVHR instead? Or proper MVHR with coanda effect terminals, or a combination of the two to limit ducts?

Interesting thought, but not sure I agree, many ASHP don't have that functional control. We are currently putting in less than an average of 1kW into the house with a 6kW heat pump, so well below any modulation, controlled on hysteresis and pure WC. House fluctuating a massive +/-0.25 degs and daily CoP generally around 5 for heating, as I get thing optimised. Generally cycling is good, its an easy way to control capacity, when below min modulation. The only caveat the run time needs to be long enough to do some useful heating, this varies with different systems, this is easy to tweak with hysteresis.

Tell us more about the system. UFH do have lots of thermostats (so plenty of zone on that also) Do you have a buffer? Do you run weather compensation? I suspect you are running the system similar to a gas boiler, as in timed running slots for heating?

Change the solar fixings to ballast trays or ballast system for different angles, so no roof welding needed?