underfloor heating insulation

ncooper1974

I am in the process of putting down underfloor heating in the kitchen.
we have a concrete floor, and will be putting down ceramic tiles.
we have just fitted a new kitchen, and left a gap of about 20mm to fit the flooring - although we haven't cut the plinths yet, so in theory we could shave some of the top if we had to increase the space for the flooring.

the guy from the tile shop suggested as its a concrete floor, we should put down an insulation board (6mm) to help heat the floor up quicker, and also prevent heat loss. he said without it, it would take longer to heat, and we have heat loss. he said if we have the space, then he'd suggest using 2 boards (12mm) so heat up even quicker.

i've spoken with a friend who laid some last year, and he said he used reflective paint instead of insulation boards, and it does the job.

Is this an alternative I should consider? anyone got any other possible solutions?

Igol

I've just done the bathroom with underfloor heating, my solution to the very expensive thermal board was 12mm plywood and, for about 60p from Morrisons, tin foil. Seems fine so far.

ncooper1974

in what order did you put these down?
either way, sounds like you suggest some form of insulation between concrete floor and heat matt, correct?

Igol

Mine was 1st floor floorboards so a little different as they are a tad warmer than concrete.

The full layout in my case was DPM, foil, ply, heating mat and tiles.

If I was laying over concrete I might have a think about flooring insulation sheets, about £8/9 for 9'x4' sheets and sticking the foil over them and the ply on that, but will depend on the room you've got to play with.

AdrianW2

Approaching this from a pure physics point of view I'm having trouble seeing how a layer of highly conductive aluminium is going to help with improving the insulation.

Igol

What with heat being transferred in the forms condution, convection and radiation you mean?
I take it you dont do the cooking

Cknocker

Got to agree, foil will not do anything for underfloor heating, it works with radiators as it is not in contact with the radiator and reflects the heat back into the room, put an electric heating element onto it it will just conduct the heat straight to the insulation.

AdrianW2

Yup. That's it.

Convection requires a fluid, which isn't present in a floor. Radiation requires a temperature difference to have any net effect (i.e. for the inflow and outflow to do anything other than balance), although if there were one that T^4 term would then be significant.

It's only a first guess, so I could well be wrong, but I'd imagine the dominant mechanism of heat transfer in a solid floor to be conduction.