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Topic Title: Electric Underfloor heating
Topic Summary: Usable as a primary heat source?
Created On: 02 December 2010 01:15 PM
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 02 December 2010 01:15 PM
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stephenbiddle

Posts: 213
Joined: 18 January 2003

Hi All

I'm trying to get to the truth about electric underfloor heating.

I've been asked on a few occasion to check out a system because the room is not warm enough. I am dubious about it's abilty to heat in principle.

Take for example a room with wooden floor and a central rug. The element is set to a limit of 27C. Is it possible to get a room to 23C by heating it through a wooden floor of which the temperature under the floor is 27C and the outside air is 0C? Other installations using ceramic floor tiles can be set to 30C, I still have the same suspicion although have no data on the thermal conductivity of ceramic tile (could be quite good).

Regards

Stephen
 02 December 2010 01:22 PM
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OMS

Posts: 19540
Joined: 23 March 2004

Put simply if the rate of heat in equals the loss then a building can maintain temperature regardless of the fuel type.

Is it practical or economic to heat a generic building and meet comfort criteria with off the shelf electric heating is another matter.

Specifically, UFH systems exploit mean radiant temperature to promote comfort so air temperature will always be lower to achieve the same perceived level of comfort. The key test will be can you get teh floor to a sensible radiant temperature based on a sub floor temp of 27C and allowing for temperature gradient through the floorbards and rug.

They can work but I suspect they are slightly underpowered in terms of W/m2 unless the whole house is designed for it in terms of insulation and air change.

Regards

OMS

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Failure is always an option
 12 February 2011 12:15 PM
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stephenbiddle

Posts: 213
Joined: 18 January 2003

Thanks for that.

I've been asking users over the cold spell and it seems that this form of heating is not really practical, without a lot of specific installation criteria being considered.

Or in plain language it doesn't always suffice as a sole heating method.

As an aside, I've just installed a system that has been damaged by the floor fitters and will put out another post on advice on possible failure mechanisms and repair options.

Stephen
 13 February 2011 07:27 AM
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normcall

Posts: 8119
Joined: 15 January 2005

Underfloor hear only works well when installed in concrete, insulated below and round the edges. The current aftermarket methods can at best only provide a background heating source and gain space by not having radiators etc.
I used to install the 'proper' UFH in the 60's and can work well.

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Norman
 27 March 2011 12:49 AM
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sparkingchip

Posts: 5900
Joined: 18 January 2003

people think they can turn it on and off like central heating, they do not understand the heat store principal and that the floor needs to build up and retain heat, just as Norm said "underfloor hear only works well when installed in concrete, insulated below and round the edges" a timber floor laid over the mat will not store enough heat to be effective.

We put one three inches under stone flags and screed, over concrete and insulation. It takes a day to warm up, but then it is great.

Andy
 04 April 2011 08:29 PM
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davidwalker2

Posts: 190
Joined: 29 April 2009

UFH will only work effectively if the underside is well insulated, otherwise you loose more heat into the ground than goes into the room. The insulation of the room/house is also a factor; and you have to do the usual heat loss calculations to determine how much heat you need to put in to maintain the target temperature at a specific outside temperature.
That said, 27 degrees sounds like getting a warm floor for the bathroom rather than central heating. And I agree, you can't keep switching it on and off, it needs to get to a stable temperature.
My system operates at 35 degrees into an engineered wooden floor (specified for UFH), no carpets, and works fine except in the very coldest weather (- 5 to -10 degrees).
David
 27 April 2011 06:05 PM
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clivewaller

Posts: 2
Joined: 10 May 2011

I remember (just about, this is from the 1960's) our science teacher telling us about an investigation he had been involved with; blocks of flats with underfloor heating, I guess built in the 1950's.

The people at the top never got enough heat, those in the middle were OK as long the people above them had their heating on and those on the ground floor either turned their heating off or had very nice gardens.

Yes, the lack of insulation meant the heat was going down instead of up. No, you won't have read about it, they weren't allowed to publish their report as it "wasn't in the public interest".

Fun fact - he only came to teach at the school so he could excavate, the Roman villa under the football pitch, and part of the villa was a hypocausts.... Oh those happy days when no one cared how many trees were cut down, or how many hours the slaves worked to keep the fires burning!

Clive Waller

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Clive Waler
 30 April 2011 07:16 AM
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normcall

Posts: 8119
Joined: 15 January 2005

I was involved in several Electricity Council (remember them?) projects trying out various ways to use off-peaking heating in the real world. Warm air was favourite for a while and even did a side by side comparison with solid fuel in side by side identical homes. That, of course, when money was actually available to experiment and test in the real world.

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Norman
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