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  • Talk to me about underfloor heating
  • Premier Icon thenorthwind
    Full Member

    Doing the kitchen at the moment and planning to put a small area of electric underfloor heating in. Not as a main heat source, but as a bit of luxury and extra heat at minimal cost (house doesn’t warrant a full wet system) while the floor is up anyway. Subfloor is solid concrete.

    The electrician is supplying the matting but I’m a bit confused about options for insulation under the matting, between the matting and floor, and the floor itself.

    Floor will probably be some sort of laminate. Some are “waterproof”, some just “water resistant” – given the location and underfloor heating, is “waterproof”ness critical? Is there are actually a difference, as in jackets?

    Is the thickness important? I’m thinking with all the layers, it may be difficult to get it level with the rest of the floor (not a major problem) – tiles that came up were about 15-20mm.

    Any help appreciated.

    Premier Icon dovebiker
    Free Member

    Is your floor slab insulated? If it isn’t, then without insulation under the heating element, you’re wasting a lot of energy. What do the heating mat manufacturers recommend? Floor levels matter if it comes to things like door thresholds and opening doors.

    Premier Icon WorldClassAccident
    Free Member

    Great as a luxury, crap as heating.

    Great for drying quilts and fluffy stuff that fills with air as it dries – lots of camping gear

    Premier Icon thenorthwind
    Full Member

    No insulation underneath at the moment, but obviously plan to put some under the matting, otherwise, as you say you’re just wasting energy heating the floor. But what type, how thick? Presumably a case of as much as you can fit, but vertical space is very limited.

    One joint to another floor (between kitchen and diner, now one room) and two doors – one to garage, with raised threshold (~30mm) and one to a door opening away from the kitchen (joint on kitchen side). So no real problem other than aesthetics and tripping.

    Premier Icon lesgrandepotato
    Full Member

    We laid 70mm of celotex under ours pretty much the bare minimum to get a viable system.

    Premier Icon TheBrick
    Free Member

    If you only have 15_20mmto play with your on insulation will be minimal.

    Premier Icon thenorthwind
    Full Member

    Yeah, I was thinking that, it’s nothing compared to standards for wall/loft insulation. But it’s much less of a problem with a solid concrete floor, from what I’ve read – presumably you don’t lose nearly so much heat than with free air under a timber floor. You can buy 6 and 10mm boards. Seems like barely anything, but better than nothing I guess.

    Premier Icon wobbliscott
    Full Member

    Great as a luxury, crap as heating.

    Err…no its not. Great as heating but electric is unaffordably expensive for anything other than a temporary boost in a small room like an en suite bathroom or something. I have wet UFH in my extension and it is brilliant and if I crank it up and open the interior doors can heat the whole house. Its also ridiculously efficient. However I do sometimes miss a single heat source to warm my cheeks on when I get in on a cold day. But sit down for a moment or two and you suddenly realise you’re nice and toasty warm.

    presumably you don’t lose nearly so much heat than with free air under a timber floor.

    Yeah, you need dried screed if you have a suspended floor construction. My brother installed that himself. Its like a dry sand mix that you compact around the pipes. The base is insulation so the pipes are encased in the dried screed. the whole point of underfloor heating is that heat transfer occurs from the pipes to the screed to heat the floor and the whole floor area becomes the radiator so having heated pipes in free space makes zero sense at all. Thats just inefficient.

    Premier Icon dirksdiggler
    Free Member

    Laminate on an uninsulated slab will be a massive heat sink. Any heat you add will get sucked into the slab and be a complete drain on your wallet.

    Unless you want to spend significant money insulating the slab just for what is essentially cheap flooring (laminate) then I would probably look at doing a slightly more expensive flooring.
    Is there a vapor barrier under your slab? That’ll also dictate what solutions you have.
    If there’s no vapor drive then I’d probably look at glue down cork options rated for kitchens. I’d think this is the most economical way to create a reasonable thermal break between your slab and your feet..
    With no vapor barrier you’ll likely need to add one.

    We just tore out carpet and pad and did 3mm cork underlayment over 6mil poly with a 1/2 cork floated over top. Crazy improvement over uninsulated slab on grade. 3 coats of 2k polyurethane and it should be bomber.

    Only way I wanted to do radiant heat under floating engineered bamboo was with 4″ XPS foam under the slab, 12mm cork underlayment and 2″ foam on either side of the footings. 100sqft of heat and this turned out to be our primary heat source in the house.

    Premier Icon bigfoot
    Free Member

    tiled lots of concrete floors with electric UFH, usually try and use a 12mm insulation board( more is obviouslly better but very rare you can get away with it) but have also had to go down to 6mm sometimes, it still works and the tiles get warm but will cost more to run.
    also you’ll loose a few 4/5mm sticking the boards down and the UFH wires will need covering with self levelling compound so probably another 8mm.

    also laminate won’t transfer the heat as well as tiles would, not sure by how much, maybe not a lot as its thin. i’ll be using engineerd oak over a wet system and been advised not to go over 20mm or it won’t work as well.

    Premier Icon markspark
    Free Member

    Have a look at the brand handyheat.co.uk, they do a system specifically for laminate/wood floors that comes printed on polythene roll that’s probably less than 1mm thick so doesn’t really add any height to the floor so more insulation can go down. Not the cheapest but their design service is very good! Used it to heat a 2 story hex shaped conservatory complete with 4m long glass access bridge🙄 and all the sheets fitted together perfectly. Your electrician just needs to add a junction box somewhere as there’s multiple cold tails as opposed to just one, so that would need locating somewhere accessible

    Premier Icon FuzzyWuzzy
    Full Member

    I have it my tiled bathroom – I think it’s got 10 or 12mm insulation under it (didn’t want to raise the floor height). It’s OK, it mostly just warms the tiles rather than heats the room (to actually heat the room you’d need it on pretty much constantly). I experimented with the bathroom door shut and it coming on up to 8 hours before I got up and the room was still cold (during fairly mild winter conditions). I’d still do it again as even taking the cold out of the tiles (that still takes 2-3 hours) makes a difference but if you’re looking at it purely for a bit of extra room heating I’m not sure it’s a great option for that.

    Premier Icon zbonty
    Full Member

    I installed electric mat from Selco in a small kitchen/laundry/bathroom area. 6mm insulated boards on the slab, tiles on top. Its a fairly chilly extension so not the main heat source- bathroom radiator does that. Providing some extra ‘cosiness’ to the tiles was well worth it for me.

    Premier Icon thenorthwind
    Full Member

    Thanks for all the replies. Sounds like it’s possible to keep the thickness down, but not ideal, which is as I thought, and I’m still convinced it’s worth doing.

    That Handy Heat carbon film claims total thickness of 6.5mm inc. 6mm insulation, so that’s an interesting benchmark for minimum size. Cheers @FuzzyWuzzy.

    Anything I should be considering when I buy the laminate flooring itself?

    Premier Icon FuzzyWuzzy
    Full Member

    You need to consider the wattage of the system you’re putting in to I think – although my understanding is that mostly effects how quickly it gets to temperature. Mine is 150w on the floor and 200w on a wall area (instead of a towel radiator), the wall one definitely gets hotter faster but the tiles are thinner to so not a direct comparison. In hindsight though I wish I’d gone with 200w on the floor to (not sure if in your case it being under laminate has any limitations on the wattage of the system though).

    Premier Icon ButtonMoon
    Free Member

    Take a look at this.

    Nu-Heat LoPro Max

    https://www.nu-heat.co.uk/underfloor-heating/renovations/

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