Correct pading for radiant floor heating?


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Old 06-25-09, 12:08 PM
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Exclamation Correct pading for radiant floor heating?

I will be getting new carpet and pading in 2 weeks but just recently decided to take out the register in the room and use my boiler and radiant heating to heat the floor. I will be heating under the subfloor. I heard there is a special pading to use?
Anyone know what this is or the name...or if this is true?
Thanks
 
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Old 06-30-09, 11:11 AM
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rugsr, Notice you have yet to get any reply. Sorry I'm so late with one... Slab foam rubber is the preferred padding for hydronic radiant heat. Nothing special, just a little harder to find and more expensive. Thinner carpeting is also preferable. Under floor heat will work no matter what floor covering is used, but it will be slightly less responsive with thicker types of carpeting and higher r-value types of padding. Some say it is less efficient, but I think that's debatable.
 
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Old 06-30-09, 12:13 PM
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Forgive me for saying but, this is not a good idea.
Placing hot water pipe/pipes under the sub floor will waste a lot of heat just heating the wooden floor and this will make it slow to react...warm up/cool down, then add the insulation under the carpet and the carpet itself and there will be a considerable time lag between the heating coming on and the room warming up.
The trouble with this form of heating is that it radiates heat in all directions but, the only real heat is transferred from a very thin connection between a round pipe and flat piece of wooden sub floor.
The better way is to enclose the pipe inside a friction fit aluminium plate that will maximise the heat transfer to the floor, and fix the plate tight up against the sub floor.
Then to fill the remaining space between the joists with polystyrene foam or similar to contain the heat radiated in the other 359 degrees.
This type of heating only really works when the pipe is enclosed inside a concrete slab, then you fix at least four inches (preferably more) of polystyrene under the slab to stop the heat going down into the basement/crawl space.
It is still slow to react to temperature changes, but at least all the heat goes into the room.
 
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Old 06-30-09, 02:59 PM
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Actually it can work quite well. It WILL be slow to react, but not as slow as it would be. This isn't the type of system that allows you to constantly change the temp, but it is usually very efficient and extremely comfortable. I would hope it would be installed by a professional who is experienced with hydronic heating, as Perry525 describes, using metal plates to increase heat movement via conduction and insulation to decreases downward heat loss via radiation and convection. BTW: It's best to use a type of insulation that can be easily removed if possible so the pipe can be serviced later if needed. Fiber glass works quite well.

The main consideration in this installation is that heat will transfer from the pipe at a fast enough rate to keep up with the room's heat loss. The installer should determine tube spaceing based on a complete heat loss calculation. This same calculation may also help determine proper setting of the mixing valve so that correct temperature of water is delivered to the floor at all times (water temp should vary based on outdoor temp...)

All that being said, under floor hydronic is a very nice form of heat. I would choose it over forced air any time, if I had it to choose...
 
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Old 07-01-09, 05:53 AM
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I fitted out an earlier home with baseboard heating, and because of the problems with heat loss underfloor heating in my sun lounge.
The rooms with baseboard heating were interesting because you never knew it was on.........it was switched on all year round and the rooms remained around 76f.......our dress was shorts and T shirts.

The sun lounge was different.. I had plastic pipe in four inches of reinforced concrete with four inches of Styrofoam under and one inch of polystyrene round the edges, finished with ceramic tiles.
The set up was controlled by a frost stat and thermostat with its own feed direct from the boiler and its own circulator/pump.

For most of the year it held its temperature perfectly 76f winter had no effect......but, I had large double glazed doors and windows all round and it faced West. When the sun came out the temperature would shoot up to 110 -120f, it was suffocating and we had to rush round opening all the windows and doors to let the heat out. You just could not breath.
Be warned!
 
 

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