Chris D

@JohnMo thanks for the quick response. I'm trying to be very careful with the spreadsheet and have done the following but may be making mistakes. Increased air changes per hour to 1 to reflect lack of air tightness. Used 'room temp' of 30 and 40 degrees to simulate the UFH with the increased delta T and then reverted to the standard room temp of 20 to calculate other fabric losses. The scenario above was for 30C because I figured for a flow temp of 40 it wouldn't result in a floor temp of that as some insulation in the overlay boards though for a room temp of 40 that would be 3.5kW. If I approach from a couple of other perspectives.... If building regs are 0.13 then at 0.3 I will have 2.3 times the downward loss of a relatively good setup. I used the link below for u-value calculation which again looking at the thermal resistance it's the diminishing returns. i.e. the first 25mm halves the u value. then 100mm halves again so whilst 150mm would be great but I don't have the headroom. https://www.gov.scot/binaries/content/documents/govscot/publications/advice-and-guidance/2020/02/tables-of-u-values-and-thermal-conductivity/documents/6-c---u-values-of-ground-floors-and-basements/6-c---u-values-of-ground-floors-and-basements/govscot%3Adocument/6.C%2B-%2BU-values%2Bof%2Bground%2Bfloors%2Band%2Bbasements%2B%2B.pdf From another perspective, if room/floor temp was 30 then double the downward heat loss I have now. By adding the 25mm PIR I half this so roughly the same downward heat loss I have currently. I don't disagree at all it would be better to have more insulation but I don't have the space and also don't have any plumbing for radiators so that isn't an easy solution either so am trying to make an informed decision. If for example I lost an extra 1-2kW downwards it's not ideal but equally compared to the >£25k to dig the floors up seems like a more sensible option.

Hi @vik2001, I’m in a very similar situation in that I have a bungalow with solid floors and no existing radiators either and very open plan so not many walls so wanting to install ufh. I ran the calcs with 25mm PIR and my P/A and it dropped the u value by about half to ~0.3 which is not ideal but not catastrophic. I also was reading around and the site below seems to agree. I’ve obviously tried to look at flow temps etc so for example using @Jeremy Harris heat loss calculator with a room/floor temp of 30c I think I loose ~2.3kw into the floor rather than 900w if I meet building regs of 0.13 but as a function of the total 14kw didn’t seem too bad to me. https://www.homebuilding.co.uk/advice/retrofit-underfloor-heating The only possible issues overlaying on PIR is compressive strength so thinking maybe XPS might be needed and a bit thicker. I realise it’s going to loose some heat downwards but it s it really that bad or am I missing something?

really helpful, thanks all, much appreciated. will take a look at the options above. Notifications weren't working hence the delay in reply.

Hi There, I'm getting prices from various suppliers for a standing seam metal roof and some cladding (~300m2 on the roof) and trying to keep costs as sensible as possible. Do people have any suggestions on the cheapest options for both the materials (though hoping I have some ok prices thus far) but more importantly on the fitting cost? I've had one person quote 3 times the material cost for fitting and not sure where to start and if that's just high labour rates or if some material options are much quicker to fit and therefore in total cheaper even if materials are more expensive? thanks in advance for any help or guidance

Hi @flanagaj and others. Did you manage to get some better prices on standing seam installation cost? I'm working through the same dilemma currently!

Hi All, thanks for the quick responses. All understood on the heat flow, was being stupid as all radiant heat. Looking at the Scottish paper and including my P/A calc it places our U value at around 0.5 so actually a reduction compared to the 0.8 I used previously however take the point about heat losses. on previous forum posts above from @TerryE it was suggested not to use flow temperature for the floor temperature in @Jeremy Harris spreadsheet and that this would only be a few degrees higher when calculating floor losses. If I increased dT by 60% which would increase room / floor temp to 27C in in the calculation this would balance out the reduction in U value from the Scottish calculation and leave it as the ~20% of heat going into slab as calculated previously. Any guidance on what floor temps to use in the calculation or corrections much appreciated.

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,