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Electric U/F Heating Makeup

Before you close it up I'd get some insulation between the joists, even just PIR cut tight or mineral wool on netting. With a suspended floor and nothing under it a good chunk of the mat's output just heats the void, so it runs longer and the tiles still feel lukewarm. If you can spare a few mm, an insulated tile backer board on the ply instead of plain backer also makes it warm up a lot quicker.
On Heatmiser, they do electric floor stats with a floor probe (neoStat-e I think), so you could run the Thermosphere mat off that instead of its own stat. Just check the stat's amp rating covers the mat wattage, a small loo mat is usually well under.

By gac · 1 hour ago1 hr
MVHR calculator

Having just spotted an error in cells Q29 to Q34 (picking up the 'night' air volume of 15m³/hr per person instead of the 'day' value of 20m³/hr), here's version 2.1.

Mikes_MVHR_calculator_public_v2.1.xlsx

By Mike · 1 hour ago1 hr
Just one big loop per slab?

The layer of insulation (between concrete and screed) will allow downwards heat travel and then slowly warm up the concrete below, but once warmed it will be effectively trapped heat until you start cooling. Then the cooling will make the heat migrate upwards until temps stabilise. It will make the start of heating slow and same for transition to cooling. But once heat soaked it not going anywhere and will be stable.

But the big BUT, your goal of batch charging with 70mm of screed engaged is flawed you're going need 100mm and more for that to be effective on a cold day. Not sure if you are single storey or two, as that will also make a difference to how effectively you store heat.

I would do UFH on top of your concrete, but choose your screed well.

Slow and batched charged floors is good. But ignore everything you have read about weather compensation, because it will not work and give almost zero advantage and plenty of disadvantages. Fixed flow temp at design day flow temps will work well and allow a high rate of heat transfer so your heat pump doesn't start modulating down to much, which you don't want when batch charging. Because of this you can also get a great CoP as dT stays pretty wide and you have quite low flow temps. This morning (4-7am) running at 33 degs for 3 hours of cosy window, I got a CoP 5.95 at 9 degs outside.

But if you are taking this approach to heating consider how you will heat DHW, as using the heat pump kills the batch charge approach very well. Just use the immersion.

By JohnMo · 1 hour ago1 hr
Just one big loop per slab?

If you go with some insulation the response time for the heating will be quicker but the heat won't go into the slab much.

By Mr Punter · 1 hour ago1 hr
Just one big loop per slab?

@Alan Ambrose +1 to saveasteading on skipping the extra XPS. With 300mm already under the raft, another layer on top of the slab just cuts the 150mm of concrete off from the pipes and you store heat in whatever screed is above it. For the overnight battery idea, thicker screed toward your full 95mm gives more mass to charge on cheap rate and slower response, which is kind of the point. Minimum cover around 45mm as he said if the slab is flat enough.
On loops, uniform layout still works for that approach, but it'll be several circuits not one. 16mm pipe tops out around 100m per loop before pressure drop gets silly. Keep them roughly equal length at the same spacing, maybe a bit tighter near the big glazing once you know where the windows go.

By gac · 1 hour ago1 hr

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BuildHub Guide: Information about the site : Introduce Yourself

Build Design, Planning, Finance and Legal

House Construction & Structural Issues

Building Trades

Environmental, Alternative & Green Building Methods

Self Build & DIY: General

Self Build Regional Groups