JohnMo

Your house is very similar to mine, my walls 1.4, floor 0.09, roof 1.3, our heat demand is 3.1kW @ -5 NE Scotland. Our temps have dropped quite a bit more than yours. So much so, that the heating has been on since the beginning of Oct. Interesting is for the average temp in Oct, our heat demand should be 1.5kW, but so far this month we are averaging at about 20kWh a day including DHW. So about 0.6kW heating input. The only thing to watch for is look at the HP output at your lowest ambient, to make sure you have some room for DHW. If you are batch charging UFH, this allows a bigger HP to be used, if doing WC you will be setting back at night a couple of degrees, so you will have a few hours where the heat pump isn't doing that much anyway.

Good chance it's air. You will need to bleed the system.

Just compared your SAP to mine, yours Jan 2100kWh, mine 1500kWh, my max heat demand (calculated) is 3kW at -5 degC. Yours pro-rated, is about 4.2kW for a max heat demand. But you need to calculate for local weather conditions. You need to add an allowance for DHW, and the reduced performance as temperature outside reduces. Plus have decent modulation. So on balance, as suggested above by @Conor would do a decent job or something similar. Ideally look for cooling ability built in and weather compensation. Bigger is not better with heat pumps.

Square hollow section. Large say 150-200mm square could have a thin wall thickness. Also rectangular could be an option.

Hope not my glulam roof beams are exposed. But I would think you would need to be on top of the preservation. Have you considered doing the structure in box section steel?

Also found this https://www.juiceelectricalsupplies.co.uk/product/dri-eco-nox-hc-nuaire-drimaster-eco-nox-ventilation-system-piv-carbon-filters/?gclid=Cj0KCQjwqc6aBhC4ARIsAN06NmO_Ys_lzHNklnO_vJ_a1Eh14_dE_0lMrfyB9mqu8KTYSGntW5-p-IwaAhTSEALw_wcB

Not sure what flow rate you need. But you could use something like this for the filter, has pre filter, H13 and carbon https://uk.rs-online.com/web/p/soldering-fume-extractor-accessories/0391359

You can do similar to PIV also.

Oh yes!

Someone said it doesn't work with UFH, so if your on radiators it should work

WC requires a flow all the time, your flow temp is right to match heat loss with heat input. So you have lowest possible heat input. The heat pump/boiler, just monitors the return temp, adding heat as required. At the moment my boiler fires up for 10mins or so every couple of hours. But the pumps run 24/7 in the heating season.

When I bought my compacfoam, I bought from GBS, was cheapest at the time.

Been there, a couple of time with various bits of our plumbing

The other way with UFH is to batch charge the floor, but you really need a thick floor. I have a 100mm concrete, charged it a 30 degs for about 6 hours over night. At the end of that time the house was at 18.5 deg, an hour later at 19 and stayed there until bedtime. Only disadvantage is you have to fiddle with it, as on really cold days the house started to cool to much over the day as the heat loss didn't match heat input.

One thing that springs to mind is the manifold pump, you can either have a mains outlet with a switch on the wall, think @joe90 does that. I have a thermostat in the hall (which I manually turn up to start pump) and wiring centre, but that is just hang overs from the system I installed. I also have Salus auto balancing actuators on three loops to automatically set a base line, which I have adjusted everything else around.

On my boiler the default was set at 20, I changed mine to 11.

That's about right. You will need the controller for the heat pump, or boiler only.

That's the idea of weather comp, you set the flow temp so you get your house at the temp you want today, as the weather cools, the flow temp increases to keep indoors stable. If it starts getting cooler indoors the curve is to flat, if it gets hotter it's to steep

Your flow temp is too high. That why the house is too warm. You should be able to adjust the curve. Your start temp needs to drop a couple of degrees. You may also need the 35 degree also reducing.

Not sure I would change, even if I had the choice. Steady temperature below the floor, about 8 degs, instead of a breeze at what ever temperature it is outside, could be -5, so heat loss could be bigger.

Ignoring any solar gains, our house sits at a steady 19 degrees. Have a big gas boiler and even bigger buffer, to keep the boiler happy. Flow temp in the floor is 23-26 depending outside temp. 192m2 operating on a single zone.

Almost the same as mine, but I have a further 150mm reinforced concrete below, and strip foundation below that. Due to being at top of a historical sand dune.

If you can get more insulation in the floor with UFH I would, this will help limit downwards heat loss.

This sheet isn't a dpc, it there to stop hydrogen bubbles forming from the reaction between aluminium foil on the insulation and the concrete in the screed.

Very environmental friendly