JohnMo

I would The above with you new lower temp radiators means your heat pump ready if you wanted at a later date. Or a combi with inbuilt cylinder. But at a later date if you did change to heat pump, you need to replumb for cylinder.

So has ours, currently sat in a 6m high lounge. Average height of other rooms 3.5m. Think my ventilation rate at the moment is about 0.2ACH, based floor area x 2.5m. And I am looking reduce that. Do you monitor CO2 and humidity? I would be careful you aren't over ventilating. Low humidity isn't good, skin and chest issues for two.

But only say distributing the flow proportionally by volume. The volume flow is generally 0.3l/s per m² or how many people wet rooms etc which ever the greatest. Trouble with the regs you either over ventilate or under. There are 2 plus dog in our house, turned the flow rates way down and still in winter the humidity is on the edge of over ventilation after a couple of cold days. If the regs didn't say I had to balanced supply and extract ventilation, (Scottish rules for airtight better than 3), would have just installed demand controlled MEV. Would have had self actuating inlet vents.

Have you attached the correct document, nothing mentioned volume. You can demonstrate via "through flow". The alternative is to under ventilation of bedrooms. You can demonstrate exactly the same way as PIV system. Unless you are getting really good airtightness, why waste your time and money on MVHR. This is a design done for my house per building regs, by Paul Heat Recovery. Notice the volume Though m³/h column.

It doesn't Granted, but will not give you anything without solar as well. £250 at 5p (without a smart meter) is 5000kWh of export. Or at 15p (with smart meter) is 1666kWh. 5000kWh represents 1 whole year of generation for me. It's not effective to pay £250. 1.6kWh escaped today and less yesterday. Would rather put into hot water and into floor via ASHP (23kWh of heat into floor today at a CoP of 4).

But don't need to include heights generally, English regs are based on floor area, Scottish floor area and height upto 3.0m, Passivhaus I believe floor area and height up to 2.5m. A very good summary is linked below https://www.paulheatrecovery.co.uk/information-on-domestic-ventilation-and-mvhr/mvhr-info-for-architects-and-designers/

Have you changed settings on the thermostat/timers since moving in? I would suspect when they tried to commission the system, they would have short cycling issues (boiler only running for very short periods) when only trying to heat 5 loops of UFH, via a mixer. So they may elected to leave the radiator thermostat in charge. So all on or all off. I would be tempted - assuming you have radiators TRVs to set the thermostat to run for long periods, let radiators rooms be regulated by TRVs, and under floor managed by mixer flow temp. I would also set towel rads to run for the same times as the radiator thermostat is set. To give boiler the best change of staying away from short cycling. Underfloor water temps are alway fairly cool to touch.

Think I would be looking at a thermally broken stud wall and cellulose fill. If the oak is structural it would be a cheap structure to do.

The company that supplied the wooden flooring gave the equipment for a a couple of weeks for free. This is basically what I used https://www.protilertools.co.uk/product/tilemaster-hygrometer-moisture-tester?gad_source=1&gclid=Cj0KCQiA-5a9BhCBARIsACwMkJ5nTcNnFTicgLKmn0qg4DdTmrZHiUQ_JRfIP6ppIcd4grcLx-VEs8kaAlAhEALw_wcB

I would do this, change the blocks marked with X for thermolite

Obvious question why? No, manifold pump will circulate. But why do you need a mixer and pump with ASHP? Just use normal sizing calculations and you need prv and filling loop.

If you have the boiler manufacturer controller they can do weather compensation load compensation and mix of the two sometimes. But loads compensation doesn't work well with UFH. Weather compensation outside temp only control, load compensation uses indoor temperature only. I would put dumb limit stop TRVs on radiators to control bedroom temps. Then do the weather compensation curve to suit UFH. Upstairs will also use heat from downstairs so unlikely the rads upstairs will have much work to do. Run it all UFH and rads on or all off.

Bigger radiators are needed. And dT is about 5 degs.

Only thing to be careful of, if you run on thermostat and not weather compensation your set point for flow temp can get a quite big overshoot. I don't have rads but did run direct from the boiler on simulated WC (resistor to give set outside temp and fixed flow temperature)

The only way to do that is way bigger radiators, big buffer or volumiser. Just keep increasing set point temp until you get the the equilibrium point where the boiler can get heat away and you have a relatively long run time. 2 degs on mine make the difference between short run times and running for hours. TPI control makes the boiler go daft. Not really, long run times have way more impact on gas or electricity consumption than lots of short cycling at a lower than optimal flow temperature. Also 10 degs difference in flow temp, is only a couple of percent reduced gas consumption. Long runs win everyday.

Hope you haven't handed over a bucket load of cash

Just looking at the graph. I would operate a little more dumb and at a higher temp. Do you need heating on at 3.30am? If not leave for as late as possible to give boiler way more work to do flow at 60+. As long as your return temp is below 53/54 deg you are in condensing mode, only marginal gains are made after that. It's going to way more efficient than your current operation. Does your boiler control have its own thermostat? or if you want to, do through Home Assistant for now just use the generic thermostat set the hysteresis to 0.5 or more

Sounds like almost every thermostat that runs TPI control is just rubbish. Maybe better just getting an adjustable hysteresis thermostat and make the hysteresis wide, but not uncomfortably wide to give the boiler something to work against.

Report MCS, that is rubbish. Looks like a monkey did it. The grey cables are exposed to UV, so unless they are specifically designed for that, the insulation will fail.

We decided on twin wall all the way. We really didn't want additional heat the single flue gave, it really became a disadvantage due the possibility of overheating the room. You need to understand room heating needs, so you don't melt. An additional 1kW may be too much. We went stainless steel and it draws the eye less, black would just look huge. Lighting the fire is easy enough.

Flexible pipes should be outside the wall not through it. All external pipes are to be insulated. Wall pipe should be sleeves and insulated.

Assume this will be chlorinated or something, so it's not a smelly pool full of nasties after a couple of days. Will make a good breeding ground for stuff like legionnaires etc...

Trouble with the heat pump it tends to be pretty small, so just heating the cylinder can be a long job - many hours. So not sure it would cope doing the equivalent of another cylinder. So that may be a non-starter. Why not just use a basic heat pump to do everything, use the hot tub thing as a huge buffer for UFH. Then a big plate heat exchanger between the hot tub and UFH. Heat pump gets super long (efficient) run times. It would be cheap enough to install, pretty cheap to run. Would be a system very flexible heat pump size. Example of what available with a short look https://www.ebay.co.uk/itm/196989855620?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=8MWPRtN6SYW&sssrc=4429486&ssuid=8KgwDlAbTJS&var=&widget_ver=artemis&media=COPY

You assume everyone can have a smart meter. Without a smart meter and a MCS install you get about 5p for export, and you can only get E7 or standard tariff, without a smart meter. So just about zero incentive to export. Currently have dishwasher and heat pump tumble dryer on and battery slowly charging. So mine is currently saving 30p per kWh (peak rate cost)

I would do a simple cascade system, with supply ducts to bedrooms only. No need to supply to dining lounge, as air would overflow from bedrooms to stairs and down to kitchen. Extract will be kitchen and bathroom only. Supply rates bed 1 and 2 say 35m³h and bed 3 25m³h. So total supply is 95m³h. If you need more flow up the flow rates slightly. Extract rates Kitchen would extract 50 and bathroom 45m³h. 45m³h of the supplied air would be taken by bathroom, the rest would go down the stairs wash through the living room and out of the kitchen extract. Whole house would be be fully ventilated. Only one easy run duct is needed. Do the ducts in 90mm and run 2 to the kitchen to a 2x90mm x 125mm plenum.