im4snow

I've seen some radiant heat installs under a tile floor, for example, where pex was used as the medium to carry the hot water.

The pex is run through some type of aluminum "device" that's intended to help heat transfer (I'm assuming). This is fastened to the underside of the subfloor where the tile will be installed.

My question is this, since the radiant heat has to "work through" the 3/4" subfloor that is wood (an insulator), I'm curious what the operating loss is vs. running the piping directly under the tile (ie, eliminate the need to heat the subfloor first).

Are there any good websites etc that discuss this issue?

snapperhead

check out www.wattsradiant.com for some info

Shipwreck

Unfortunately pex has a pretty good expansion coefficient so I don't think trying to bed it in the thinset would work,I use the electric matting for this reason.I do hot water radiant systems also and when the tubing is against the floor with the reflector plates,the water runs at a lower temp the thickness of the subfloor is taken into design consideration.The subfloor becomes a part of the thermal mass storing the energy brought up from the hot water, instead of insulating against heat flow up into the tile floor.

nhmaster3015

Wood floors do indeed effect the thermal efficiency of the loop. Thick floors and those with carpet pad and carpet perform even worse and require much higher water temperatures than in floor (thin-set) radiant piping. Typical temps for in floor run 85 -95 % and staple up systems can run as high as 180% Naturally, running higher water temperatures has a negative effect on the overall system efficiency, but people like the comfort aspect and are willing to make the ectra expense for the system.

Dr Heat

I agree that carpet and pad has an effect but a 3/4 inch subfloor is like R .75 rather insignificant and as stated earlier it accounts for mass. Even thin set will hold heat. you just need to figure it into your calcs.