JohnMo

It was the soak away area design guidelines, it states sizes for differing drain away time from the perculation test. But states if it fails the perculation test, you size to a given criteria.

You would need insulation, or not comply with building regs.

An Ivar mixing valve allows you set the bypass flow independently of flow in and mixing ratio of hot and return water, opening the bypass would mean return water is hotter sooner, so the heat pump temperature output increases quicker - I think. But is this realistic? First hot and cold spots all over the floor. No one ever runs an UFH with 20 dT. Possibly for good reason. Then you would have make sure your radiator system could flow enough to keep heat pump happy. Or install bigger radiators upstairs?

See photo up thread of blocks. PIR is on inside of block and floor screed taken up to PIR. Used 70mm PIR upstand around the whole inside perimeter of the floor.

I would invest in some insulation, then the room wouldn't go cold when a thermostat switches on off. Or are you trying to heat a warehouse with a single heater? Last house managed to heat my garage with a single electric heater, it was fine.

Where is the insulation going?

Not something I could agree with, it's the whole cost of the MVHR system, not just a single high cost component. Next logical step in ventilation would be demand based MEV or dMEV, so the trickle vents would be self actuating, and ventilation fans run at a flow rate dictated by humidity and/or CO2.

I used this for my roof lights upstairs, very easy to work with, but during our build was readily available in the size I needed for doorways during COVID.

Both the thermolite and the Marmox are covered up (Marmox from UV, thermolite from atmospheric moisture) - so are they not equal, with different advantages and disadvantages? Install a PIR upstand inside the thermolite block, the bridge has gone anyway. The other factor is what ever sits on the Marmox block has to be wider than the block, the block cannot be an wider than anything sat on it. Thermolite doesn't care so offers a likely more flexibility for construction. Sorry not correct units - those valves are R value, not U value. Then you to take account of the dimensions to get the U Value

I would read the data sheet (attached) there are rules you need to follow. Thermoblock_Technical_Brochure.pdf But I used thermolite blocks and had no issues, would do so again. Also have a PIR upstand inside the thermolite blocks. So little or no heat escapes.

You may need to be a little more specific with what area you are talking about, Scotland is pretty big.

You just have to be careful the terminology is correct. A lot of systems can be hydro split (water split), while others and more appropriate to the term of split, are refrigerant split. Both are available. The Viessmann reference above is a hydro split.

True, it's a package of upgrades that go hand in hand. Good airtightness, needs forced ventilation, so why not have heat recovery as well. If you aren't reasonably airtight airtight MVHR is a none starter, costing you money every minute on, payback is never, in that cases.

The formula for calculating ventilation heat loss is: Rate of heat loss = V x ACH x DeltaT x 0.33 So if we take the efficiency of MVHR as 85%, some better some worse. The formula becomes to calculate savings V x ACH x DeltaT x 0.33 x 0.85. So if you flow rate through MVHR as 0.3 ACH. A 200m² house with 2.4m high ceilings, inside temp 20 outside temp -3 (200 x 2.4) x 0.3 x 23 x 0.33 x 0.85. So you are saving just over 900W against a ventilation heat loss of 1100W, without heat recovery. That is worse case. So a more average winter temperature of 6 degs The saving becomes an hourly savings of 600W throughout the heating season. 600W x 24 hrs x 180 days. So about 2500kWh. So @joth numbers are in the correct ballpark. So a CoP of 4 or gas, so around 5p per kWh. 2500 x 0.05, is about £125 a year. My first quote for MVHR was £10k so that for us would have been about 80 years payback. As it is I am still looking at 16 years as DIY installation. So you only paid £1000 for the full system?

Good old days when energy was a cheap, no-one cared how much energy they used. And the whole house was cold except 2 foot away from the heater. If you want an even spread of heat use several heaters.