Electric Underfloor Heating

[leevis]

Hi All
Currently building an extension and thinking a bit ahead. The extension is going to house a kitchen (the total size is 6m x 5m) which will contain a smallish utility room. Layout will be units down each side and an island in the middle.

I was looking at putting a radiator in there but trying to find a decent location is going to be tricky so was thinking about putting in electric underfloor heating.

My boiler is a bit old and really unsure if an extra rad will push it over the edge and underfloor water heating is not an option.

The flooring is a concrete slab on which will be timber studs with 50mm celotex installed inside. On top of that will be 22mm (or maybe 18mm) chipboard flooring. On top of this will be (ultimately) laminate flooring.

My reasons for thinking about underfloor electric heating is it will be everywhere that it is needed. I am assuming here that it can be installed where there is foot fall and not necessary where the units are and the island etc so i can place it where i think it is needed.

What i was thinking was to get it everywhere there isnt going to be units/island and then do the same in the utility room to give that some heat.

Looking online there appears to be some decent thermostats nowadays. I remember in the old days where these were not too efficient.

Anyway, my questions are

1. Is it reasonably efficient? (internet says yes but wanted a real person opinion)
2. Can i install this my self?
3. Is it worth it?

L

 

[Taylortwocities]

My opinion:
1. is it efficient? No. It will take a good hour to warm up a floor area. And that is basically all it will warm. You’ll notice the floor is warm when you walk in bare feet, but it it not good as a space heater. You could fire up the oven and leave the door open.
2. Can you install it? Like everything, it depends on your Level of competence. Like every electrical installation, it must comply with BS7671. There are specific requirements in the regs relating to if your heating system also requires an earth grid, the IP rating of the flooring, RCD protection? Maximum allowable floor temperature etc.
3. Is it worth it? Not in my opinion. A wet system(rads/underfloor) is a much better bet.

PS Don’t take advice from electric floor makers on how great their products are. They are bound to big them up!

 

[ericmark]

There is rayochem I think it is called that is self regulating, so you don't need pockets and sensors in the floor to stop it overheating, however underfloor heating be it electric or water has a huge delay between switching on and getting room warm, so only really suitable for rooms occupied 24/7 like old peoples homes.

The kick space heater is the reverse, it heats up fast, and is very good for rooms like kitchens, but electric and water heated is available. Main manufacturer is Myson. Even without the kick space option the fan assisted radiator means less room needed for the heating.

As to boiler size, over the years we have all fitted double glazing, cavity wall insulation, loft insulation and better sealing doors, so likely there is plenty of spare capacity with the old boiler.

I put in underfloor heating for mothers wet room, fortunately also a towel rail, as to be frank it was useless, 27°C is max floor temperature, think about it, 7°C difference, on a hot day when living room is at 28°C due to sun and it is 21°C outside we open all the windows to let the room cool, just note how slow it is to cool, then think with under floor same in reverse just 7°C difference it simply will not work on its own, as an extra yes maybe but as sole heating no.

Look at kick space heaters.

 

[winston1]

Electricity is four, yes four, times the cost of gas. That is all you need to know.

 

[leevis]

OK i get it. Looks like a radiator is the best option here. Kick heaters not possible.

I did a quick "how many BTU do i need" and it came up with 11K BTU's. Question is if i have to put this in a corner, will it heat the opposite side?

 

[ericmark]

Opposite side yes, that's how they work. it is 90° to heater that could be a problem. When your forced to use a fan heater with built in thermostat, set at 2 kW you realise how little it runs to keep a room warm, I had a Myson in the old house, not a lot of sound, but you could hear it run, and it did not kick in much.

How any of the heat calculators work I don't know, I back in late 1970's fitted the central heating very carefully calculated, but it does not take into account the amount of heat which went up-stairs, so up-stairs far too hot and down-stairs too cold, and the extension when built had loads of insulation in it, cavity wall, floor and roof, so again did not need anything like as much as the calculator said.

 

[SimonH2]

... and underfloor water heating is not an option.

Is that because you don't think the boiler can cope, or there's a specific reason it can't be installed ?
Is your slab already in place ?
Ideally, you install a wet system in the slab as it's being installed - clip the pipes to the insulation, pour the concrete on top of it. Because wet systems have a significantly higher power transfer capability (from the hot water to the slab), even heating the whole slab is not as slow as you might think.
If the slab is already there, there are low profile wet systems that can install in the amount of space you have available.

Bear in mind a fundamental difference between wet and electric systems.
Electric systems are a "constant power per unit area" system - so if you insulate a section of floor (with a rug, or by putting a kitchen island over it) then that section will run hotter until heat losses match the heat input. This means you'd be right to avoid putting an electric system under the units - just on safety grounds.
A wet system is more akin to a constant temperature system. Your floor cannot (other than for brief periods if the water goes cold for some reason) be hotter than the water you heat it with. That means, no matter what you put over it, the floor cannot get hotter than the water heating it. You might still want to avoid putting the system where units are known to be going round the outside, but you might want to put it under the island in case you change your mind later. If you are heating the concrete slab, then it would make limited difference anyway as the big lump of concrete will conduct some heat into unheated areas anyway.

Obviously it won't work if you heat the slab, and then put 2" of insulation on top of it as you are currently planning.

So, if you have not yet poured the concrete slab, then I'd suggest re-considering your plans. Insulating under the slab and using wet UFH may be a better option.