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Heating and cooling: Low profile UFH

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  1.  
    • CommentAuthorErkindik
    • CommentTimeNov 13th 2022
     
    Hi everyone - hoping for a bit of advice… we just moved into a 1970s detached house. We want to install UFH as part of an effort to get the house ASHP ready and because we just don’t like the look of radiators in rooms! We plan to change the floors, skirting and doors so it seems like a good moment to install UFH. I’ve lifted up some flooring and can see the ground floor is a concrete slab. I don’t know what, if any, insulation is underneath it. We don’t have the funds to dig up the floor and build down to install more insulation. I’ve read about low profile UFH systems with a finished height of only 15-18mm, which would probably be ok, but I’m not sure if they would work without extra insulation.

    Has anyone installed a systems like this? What sort of performance have you seen?
    • CommentAuthortony
    • CommentTimeNov 13th 2022
     
    Perimeter insulation or wing insulation, no insulation = high heat losses and high energy use = high running costs
  3.  
    Even with 300mm EPS insulation under the slab you would be losing around 8% of the energy used for the UFH, to heat the ground. With 10mm of insulation you would be losing the majority of the energy to heat the ground. If you don't like the look of conventional radiators, have you considered skirting radiators. If you are considering replacing the skirting anyway, that seems a good compromise. The only way to install UFH without wasting large amounts of energy running the system is to dig up the floor and lay at least 300mm EPS or equivalent insulation under the slab.
    • CommentAuthorTimSmall
    • CommentTimeNov 14th 2022 edited
     
    There's very likely to be no insulation at all underneath the concrete. Usually the ground temperature will be at about 10°C year-round (bit higher in autumn, and a bit lower in spring). The temperature on the underside of the flooring is likely to be about 2 or 3 degrees below room temp. With an indoor temp of 20°C the temp difference between ground and bottom of flooring will be about 7°C.

    With UFH you'll probably be operating at 35°C or higher. That increases the temperature difference across the flooring slab (and so the heat loss) from ((20°C - 3°C) - 10°C) = 7°C without UFH, to: 35°C - 10°C = 25°C. So you'll increase heat loss to the ground by about 3x or 4x.

    So unless you're prepared to break out the concrete and replace the floor entirely (possible, but hard work, disruptive and messy), then you may be best getting down whatever insulation you can, without UFH.
  5.  
    In our last house we* dug out a concrete floor and replaced it over thick insulation and DPM, together with IWI, and it transformed the 'livability' of the room, we could sit comfortably on the floor and play with kids etc. The reduced heat losses meant we got rid of two big radiators and just had one small one.

    *Actually someone else did it for us, while we vacated, horrendous messy expensive job.

    However, we probably won't do that with our current house because the carbon released by manufacturing the insulation and concrete slab will likely be worse than what is saved from the reduced heat losses.

    So we are also looking at the low profile polystyrene boards that come with precut channels for ufh pipes. We noted that the insulation is thin so heat losses are high, as was mentioned above, so ideally we would lay additional insulation below the ufh boards.We'd also have to lay 18mm timber over the top for impact resistance, and floor covering on top, so the total build up gets rather thicker.

    You can get low profile ufh based on cement boards rather than polystyrene, which don't need the timber layer on top, but do need more insulation below.

    We found previously that adding height to the floor is less of a problem than you might think, we had one floor 40mm higher than another and the difference was taken up by 20mm tapered profile oak thresholds in the two doorways between, no problems.

    However we have a fitted kitchen in the room in question so we decided to delay raising the floor until we replace the kitchen.
    • CommentAuthorJeff B
    • CommentTimeNov 14th 2022 edited
     
    Posted By: WillInAberdeen

    We found previously that adding height to the floor is less of a problem than you might think, we had one floor 40mm higher than another and the difference was taken up by 20mm tapered profile oak thresholds in the two doorways between, no problems.


    I can concur with this. I did exactly that in my brother-in-law's place and yes, the timber "ramp" was scarcely noticeable. I would love to do it in our lounge but SWMBO is concerned that we would not be able to re-install the fitted carpet properly, apart from all the disruption of course. It would have been an ideal time to do it now as we are installing IWI in this room* but I must admit it is a headache moving bulky settees/armchairs about the place!

    *Looking forward to testing this out when ambient temperatures return to normal for this time of year. Currently room temperature doesn't drop below 20C overnight with no heating.
    • CommentAuthorcjard
    • CommentTimeNov 25th 2022 edited
     
    Posted By: Jeff BSWMBO is concerned that we would not be able to re-install the fitted carpet properly,.


    Most of the carpet fitters I've met aren't wizards that know something the rest of us cannot fathom; I'm not sure I'd let a concern like that hold up an eco renovation; you could always ask a fitter to come round and reinstall the pre cut carpet as most of the tricky bit has already been done in terms of sizing it
    • CommentAuthorbxman
    • CommentTimeNov 25th 2022 edited
     
    There's very likely to be no insulation at all underneath the concrete. Usually the ground temperature will be at about 10°C year-round (bit higher in autumn, and a bit lower in spring). The temperature on the underside of the flooring is likely to be about 2 or 3 degrees below room temp. With an indoor temp of 20°C the temp difference between ground and bottom of flooring will be about 7°C.

    With UFH you'll probably be operating at 35°C or higher. That increases the temperature difference across the flooring slab (and so the heat loss) from ((20°C - 3°C) - 10°C) = 7°C without UFH, to: 35°C - 10°C = 25°C. So you'll increase heat loss to the ground by about 3x or 4x.


    All very true But once the soil below the the floor has warmed up how fast is that going to continue I am convinced the loss will reduce to a fraction of that expressed above .

    the Delta is going to decline to practically nothing.


    Dry soil, after all is not a very good heat conductor .

    As Tony says it is the perimeter where you need to concentrate your efforts IMO.

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