JohnMo

Buying at full price, I would go Panasonic monobloc and just go to City Plumbing or Cylinder2Go (you get a discount )for the cylinder. Then you just need an UFH manifold. Next job - do your pressure drop calculation assume a 100m long UFH loop and then use your pipe length to sort out primary feed pipe sizes. You want to be getting around 1.4m³/h flow rate (assuming 6kW), to keep UFH and cylinder happy.

I found with boiler it's super efficient at heating via UFH. I run at a fixed temperature, chosen so the boiler runs without stopping when ever it's on (when it's been below 5 degs for more than 6 hrs - hybrid install). And running against a heat pump cylinder generally runs about 4 degs hotter than the cylinder ends up. So about 56 degs max temperature.

Forgot to mention - one thing goes wrong generally the whole thing is toast. Monobloc and 3rd party cylinder every day.

So why the bulk of the all in one then? It basically moves most the stuff of a monobloc inside? Big box small cylinder and from the looks a £1k plus cost premium. Easy plumbing for a premium price. Until you realise most the time in points are exactly where you want them, they have zone valves not needed, basically plumped for S plan or similar, which you don't want. My 210L came with 3 port diverter, expansion vessel, combi valve, and elbows, for under £1k, pre plumbed was nearer £2k, piping in wrong place for easy tie-ins, loads of stuff not needed.

Why do you need a pump? Why 2 port valves, you just a 3 port diverter! You definitely need an expansion vessel X2 one for DHW cylinder and the other for the heating system. All in one cylinder (assume you mean pre-plumbed) full of sh*te you shouldn't need. Would be my opinion. Reality is you need a 3 port valve and some isolation valves. If you do need an additional pump due to pipe length (distance from ASHP) you will just add a fixed speed pump on the return line after cylinder and UFH tee together.

It's on the low side, but still ok. Ours fluctuates between low/mid 30s to mid 50% depending on the weather. Have found we almost never need boost either. If it sitting consistently at 36% and below I would considered dialing down the MVHR flow rate a little. It's doing what it needs to. Also look at the way you boost, you may not need it?

The stuff I linked to wouldn't need the liner and is £25 a sheet.

I think the insulation material is this https://www.thepackagingdepot.co.uk/s-1241/1200mm-x-2000mm-x-25mm-white-foam-sheets/?srsltid=AfmBOormE9cYSfOuxypkmQFxMf25Te6Zgn3pYwoIJnoQGgXQ6KlRuT00z-g

Wish it wasn't the heating season for us, we nearly got to the point of thinking about cooling and temperature took a dive. Average temp here the last week has been between 6 and 8 degs.

I PIR in our foundation, but I used long screws about 150mm long. Just pushed through and when it came to break it out just smashed it all out. Our concrete above the floor insulation was 100mm so used a 100mm PIR former. Once I had sorted the drains etc, just back filled with concrete by hand.

You could used XPS - Extruded polystyrene. It's pretty tough. But why do you need insulation? If you do make it inside out, hard stuff inside, EPS outside.

When we first had the MVHR running we were getting similar, so tweaked up flow rate in bedroom and lowered elsewhere, it never goes above 1000ppm (window closed and door closed). Now with window open most nights it's closer to 600ppm.

Would doubt it's EPS, been working with it for a few weeks, and it would soon fall apart in a a rotating composter. Looks more like @Iceverge says.

Mdpe is fine, just look in most farmers field, mdpe pipe been there for decades. Underground plastic drain pipe will turn white and may go brittle. Armour cables generally UV stable.

Just about any expanding foam filler is ok with EPS. Dampen the edges of the EPS just prior to the expanding foam. It helps with expansion and curing.

If you want him to be notified, you type @ then carry on writing his user name and a drop down appears pick from list. Then you get @Nickfromwales and he is notified.

Not able to open a .ods file?

You don't Shop around and buy what you want - simple. I couldn't be bothered guessing, or messing about with odds and ends, so I shopped around, bought exactly what I needed.

Not a good start

MEV mechanical extract ventilation - so just extraction, but ONLY when needed. A simpler system with dMEV could be done with no ducts

Yes. A ducted single fan unit like MVHR but without the supply.

If I did it again (unlikely) I would just do demand based MEV. Humidity control trickle vents, humidity control wet room terminals and automatic speed control on the MEV unit. No filter to change, one fan, only running when actually required and only in the area needed.

You do two layers with staggered joints. The layers can be equal in thickness or not, it doesn't matter.

Maybe, but they have to follow all MCS guidance. So unless you have an actual air test they have to use the MCS figures for ventilation heat losses etc. To take credit for MVHR it has to be installed and commissioned etc etc. I just couldn't be ar£ed with all the faff to get very little in return.

Must be missing something. Your flat roof already has a fall, looking at the brickwork, so why do you need to make another fall?