Underfloor heating and insulation

S

sparkyspike

I have a customer (I'm an electrician) who wishes to have an underfloor heating mat installed direct onto screed. The concrete floor is about 3" thick on top of jablite insulation. It will be tiled with natural slate.

Obviously I have advised that insulation boards are the best option, but they have a problem with matching threshold heights etc, so they want to avoid this. Plus, I think, the cost is a problem.

Topps Tiles recommended a 1mm waterproof mat under the heating mat, and they insist it does have thermal properties. I'm a bit skeptical about it though.

What I need advice on is whether laying direct on screed does dramatically increase warm-up times and running costs (so much so that it can't be done) and more importantly, affect the final temperature of the floor. A tiler once told me that tile adhesive is thermally conductive - more so than the screed - which is why a 100mm gap is normally left around the edge of a floor area.

I am happy to lay the mat onto the screed, unless I am advised otherwise. Any thoughts?
 
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Have a look at this page. http://www.handyheat.co.uk/underfloor_heating/which_underfloor_heating.htm

If you don't insulate, then the floor will still get warm, but not as warm as it could. It'll also take a lot longer to get warm.
It depends whether you want to be know as the electrician that installed the UFH that doesn't work very well. ;)

A tiler once told me that tile adhesive is thermally conductive which is why a 100mm gap is normally left around the edge of a floor area.
To a certain extent, but more likely done because no one walks that close to the wall.
 
S

sparkyspike

Thanks - I had a look at the link. I was interested to see that in new builds, the cable is laid in the screed. So no insulation? Why then would you bother with insulation on top of screed for a retro fit installation?

I guess I'm not convinced either way yet. I don't want to be known as the electrician who's underfloor heating won't work, of course. I also don't want to tell a customer that they absolutely MUST fit insulation boards, when the benefits are small, relative to the installation cost. Can you give me an idea of how much more efficient insulation boards are and how much warm-up time is diminished? No undefloor company seems to have this information.

Has anyone actually used 1mm matting as insulation?

Also, has anyone installed underfloor heating on bare screed and seen good results?

:confused:
 
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Can you give me an idea of how much more efficient insulation boards are and how much warm-up time is diminished?
No links for ya on that one. What you need to be realising is that without insulation they're only suggesting that UFH is any good for warming the floor. With insulation it can properly contribute to the heating of the room. It depends what your customer wants.
 
S

sparkyspike

Sorry - I should have explained. The underfloor heating is just for warmth underfoot. The room heating (it's a kitchen) is from a wall mounted radiator on the central heating system. The underfloor heating will not be a sole source of heat. I suppose this makes a difference.
 
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The tiles will get warm, no doubt about it. So long as you explain to the customer that it's not a very efficient way of warming up the tiles and they'll be wasting their money heating a slab on concrete, then you've done as much as you can. You can lead a horse to water.....
Personally, I won't have UFH in my house - wear a pair of slippers and you have no problem.
 
S

sparkyspike

Thanks for the replies. (Except for the last one, that was just silly...)

As the concrete is insulated with jablite and it is 'normal' to fit heating cable in the screed, or on it, then at least I won't feel as if I'm being negligent in any way - as long as the customer is aware that they could save running costs with the extra insulation.

Cheers
 
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Thanks for the replies. (Except for the last one, that was just silly...)

Aw shucks man,did it not even make you smile? :LOL: ;)

Incidentally ufh manufacturers will always advise you to use insulation as it is going to increase their sales.Whenever I have fitted it I have always explained that it is not great as a heat source and should only be seen as way of warming the tiles underfoot.

http://www.warmup.co.uk/uk-running-costs.phtml
 
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How did you get on with this?

I am in a similar situation, I have the screed going down in a conservatory soon and looking to have UFH on this. I assumed I would need insulation board but the electrician doing the work (has done plenty before) tells me as the base is insulated then I dont need it and it willbe fine on the screed layer.

Not one to let people get on with it, I always like to know whats going on a why.
 
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just to pick up on something mentioned before, behind doors and right up to walls is not needed for ufh, if your not gonna put your tootsies on any area its just a waste.

i personally hate the stuff. but each to his / her / its own
 

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