electric underfloor heating issues....

[jimborulezthewe]

right... well... i originally thought my lovely new underfloor heating wasn't working at all... its been on for 2 days solid now and the floor temperature has gone from a rather cold 15 degrees to a somewhat disappointing 25 degrees and that seems to be where it's stopped...
the floor heater is a 100W per square metre mat laid on a concrete subfloor with adhesive and then 10mm porcelain tiles over.
my question (eventually....) is... does all this sound about right? i mean, the floor temperature now is nothing to get excited about, does this sound like a dud heater or is it more likely that the idiot who installed said system (ahem...:blush2 didnt think things through and should have insulated the floor better and stuck a bigger (200WpSQM) heater down?
i'm kinda hoping someone can reassure me and tell me the heater isn't working properly, if not i'll have to go find a suitably dark, damp corner in which to stand whilst hanging my head in shame for being a dunce and generally just messing it all up... (again)

many thanks in advance for any input, or perhaps any abuse you feel you may want to point in my direction having read this......

Jim

 

[diamondtiling]

Did you have any insulation laid? is there insulation such as Kingspan laid in the concrete?
If not the heating will be going straight into the concrete slab and will warm this up first before the tiles.

 

[hillhead]

With diamond on this.was there an insulation board even under the mat?

 

[jimborulezthewe]

erm.... no insulation in the concrete as far as i know and i didnt put anything other than the primer down on the floor before laying the mat.
beginning to think i should have put more thought into this little venture...
thanks for your speedy replies guys

 

[diamondtiling]

It will eventually heat up but it will take longer. The tiler should have been able to advise you regarding thermal boards. How long has it been down?

 

[Dan]

Yeah, I'm with the above. You've selected a tile warming system (100W/m2) and have zero insulation. I think achieving 25 degrees is pretty good for that setup.

Porcelain tiles are good with underfloor heating as they're so dense, when the bottom of the tile heats up, the top does soon after. Ceramics not being as good due to the biscuit that forms the main body of the tile not being so dense.

If you'd have used insulation directly under the heating you'd have found a difference, though I'd have still not expected much more than 25 degrees, you'd find it would just heat up much quicker.

The perfect setup (and there's no reason not to go for it on concrete, on wood or under laminate it can be an overkill) would be to use at least 10mm insulation board under the heating and then go for 200W/m2 which is sort of classed as a primary heating source, so that would heat the room properly.

It's a shame really as we see this quite a bit and it's normally out of the question to re-do it all. You should have read up on it a bit more and searched the net, almost all heating suppliers will tell you to go for the most you can afford or the most the floor can cope with, because you can always turn the dial down if it's too warm, though you can never turn it up if it's too cold. You'll also find your bills are higher than with 200W in your case if you're trying to keep it on 12 hours a day just to get an hours use out of it. 200W could be on 20 minutes before you use the room and turn off as you leave and actually would cost a lot less to run with insualtion involved.

** points to the corner **

 

[jimborulezthewe]

in the words of homer simpson.... D'OH!

I'll be in the corner if anyone needs me... which they wont...

just out of interest, what sort of current draw would be a reasonable figure to expect? i've done a few child-like scribbles and come up with a figure around the 3AMP mark, sound about right for a 7MSQ area? i only ask as i did hook a current clamp meter round one of the heating cables and found the current flow to be ridiculously low, about 10milliAMPS, which just completely baffles me

ho hum, i'm an idiot

 

[diamondtiling]

Have it checked by a qualified electrician, I do install but all the wiring up is done by a friend of mine. There are many types, some just take the chill off the tiles, others can be used as the primary heating source.