Hi All, after many hours reading and investigating I thought perhaps easier to actually post my query on here so please be gentle with me if I'm being stupid.
We're planning a large refurb of a ~250m2 bungalow which is currently heated with 70's hot air blown heating which is noisy and unpleasant.
Floors are currently solid concrete.
Proposal includes lots of glazing and external cladding and insulation but nothing on the floor.
As no radiators or pipes at present we'd much prefer UFH but don't have much height so are looking at the low profile matting systems like nu-heat, ambisolo, etc.
I've read the hundreds of posts saying you need insulation under UFH to minimise heat losses and am trying to quantify this to make an informed choice and there are lots of competing elements, heat rises, flow temps, floor covering, etc.
Using Jeremy's amazing heat loss spreadsheet I think I've worked out that approx 20% (2kW) could be lost into the floor with no insulation (assuming concrete u value of 0.8). I think my absolute numbers are wrong as I think the spreadsheet concludes 50,000 kwh/yr and currently with v poor insulation it's still only about 25,000 kmh/yr.
So my dilemma which I'd appreciate any advice on is that does 20% heat loss into an un-insulated floor sound about right? if so even with current bills that would be ~£700 per year into floor heat losses which whilst bad, compared to the cost of digging up and re-laying 250m2 of concrete, new skirting boards, etc. would still take a very long time to pay back even if you saved the majority of this. .
Any suggestions or ball park estimates to quantify proportion of losses into the concrete floor pre and post insulation would be much appreciated.
Thanks in advance,