Elelctric under floor heating - laying onto concrete

Hi all,

Currently doing the kitchen, and have decided to install electric UFH under the whole tiled floor. The floor will be tiled in ~8mm thick porcelain tiles, onto a concrete floor. The concrete is about 75mm thick, laid directly onto hardcore.

The UFH is only there to make the floor warm to the touch. We have plenty of heating from the CH to heat the room.

In a perfect world, I'd dig up the concrete, dig down about a foot, insulate and screed. But I'm not going to do that. I'm just going to tile the floor. What I'm trying to decide is whether to tile directly onto the concrete or onto some kind of board material fixed to the concrete.

Half inch WBP is an option, and would provide some insulation. But I'm wondering if I can get a sheet material (1/2-3/4") that will be significantly more insulating than the ply, or if I should bother with any sheet material at all, or just tile onto the concrete.

TIA

Reply to
Grunff
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Are you even able to put the electric under floor heating on top of wood? I seem to remember that you can't but am willing to be disproved.

OT> a while ago when I was an engineer, I was looking at a circuit board disapating 1W over about 1"sq and without additional cooling it was reaching

120oC. Moral, without somewhere for the heat to go things soon get very hot indeed, so I'd be tempted to go onto the concrete with the heater.

Scott

Reply to
Scott Mills

The key is the thermal resistivity on both directions., Yo can lay hot elements on top of insulation on top of wood if the heat transfer in the other direction is good.

Reply to
The Natural Philosopher

Manufacturer says not a problem as long as shrinkage of the wood isn't a problem. I'm intending to dry it out thoroughly before tiling with a flexible adhesive, so no problem there.

Ah, but I bet you didn't have a thermostat in the middle of your board that cut power to it when the required temperature was reached :-)

All makes good sense, and if this was the primary room heating I would want to do this. But it's really just a 'nice to have' addon, to provide nice warm tiles to walk on. Electric is considerably simpler, especially given that I would much prefer to lay directly onto the existing concrete.

But your argument about heat having somewhere to go has certainly swung me a little in favour of a non-insulated aproach.

Thanks.

Reply to
Grunff

I agree with that in principal. However, in reality you will could a large amount of localised heating under the wires, depending on the power output this could become quite high.

Reply to
Scott Mills

Scratching my head and parsing that, I think the correct response is that U/F heating is, at most, about 100-150W/square meter.

That is NOT a huge amount to get rid off.

Reply to
The Natural Philosopher

Phew! I thought I was being stupid!

I've gone for 120W/m^2.

But I can kind of see if it was on a very well insulated floor, with only the top surface to dissipate the heat, the steady state might me quite hot. Irrelevant since I have a thermostat.

Reply to
Grunff

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