UFH thickness

[cakeman72]

My kitchen is currently stripped down to bare plaster and screed in preparation for reno. I had an idea to install underfloor heating, not as the main method of heating the room (already have radiators) but to add a layer of comfort, allow the floor to dry quicker, and to help combat mould and other damp related issues. This is an area of only 5 square metres.

The floor is currently screed on top of solid concrete , with no insulation. It will not be possible to install the normal amount of insulation because I'm not digging up the concrete, but removing the 6cm of screed is no problem. Since there would inevitably be a lot of heat loss downwards the UFH would be used only as and when, such as after mopping the floor or when entering the room on a winter morning. My questions are:

1. Is 6cm enough for the complete system including screed? I'm ignoring insulation (I don't care what building regulations have to say in this regard) but would consider any systems that include a small nominal amount of insulation or innovative methods such as vacuum insulated panels, provided they fit inside the available 6cm thickness and aren't a complete shot in the dark.

2. Am I better off with a wet or an electric system, considering the intended purpose of the UFH? Other areas of the house already have wet UFH so the pump manifold and controls are already there.

 

[Madrab]

Use an overlay system, ideal for the retrofit you are taking on. You could take out the 60mm of screed and then use say 40mm of EPS400 solid insulation, or even 20mm plastic coated chipboard then 20mm insulation then use the 20mm EPS400 routed boards, that is slotted and foiled to take a 16mm pipe loop. Then you can cover that with any desired floor covering directly on top. It is used as an on demand system and can run with the rads, as it reacts as quickly as they do. As it only has to heat the floor covering above it (no thermal mass) then there is little thermal waste downwards, due to the insulation it sits in and that is underneath.

Depending on the temp your CH runs at and given it's a small area then this can probably be fed directly off the CH with a RTL valve installed to regulate the floor temp down to the required level.

 

[denso13]

I'd consider electric for such a limited area, for secondary heating only, laid on insulation boards designed for the job.

 

[ericmark]

I fitted electric under floor heating in a wet room, under the tiles, with a good 9 inches of insulation below the wood it was laid on.

It was a failure, I will explain.
1) Once the insulation was fitted, the floor never really got cold anyway.
2) In a wet room, idea was it would dry the floor so not slippy, but it took over an hour the dry if floor not swept of standing water, and around 15 minutes if a squeeze was used, and did not matter if UFH on or not.
3) I would take a good hour to feel the slightest bit warm, and two hours before it felt warm to walk on, so the idea of switching on before taking a shower, did not work, also the shower would cool the floor, so it was not warm while having the shower.

The sensors failed, and got jammed in the pockets, so we should have stopped using it, but it had a job getting to temperature anyway, it did not heat the room, lucky the towel rail did.

There are two types of electric UFH the resistive and the chemical the latter it seems is far better, the chemical type can't overheat, as the temperature raises the resistance increases, so it self-regulates, but for the wet room, it would need an earth mat over the top of it, where the resistive came with an earth braid around the resistive wire. But I fitted it nearly 20 years ago, and likely there are now new versions.

I would say just use an insulating floor covering, and forget UFH. It has been tried in the past, and the Roman hypocaust seems to have lost popularity. But people will reinvent even the wheel.