radiant heat not warming the floor

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  #1  
Old 11-12-08, 04:13 PM
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radiant heat not warming the floor

I just installed radiant heat in between the floor joists of the 1st floor (basement installation). The system is working but the floor is not warm. We remodeled our old kitchen and the floor was weak so we reinforced it before installing the tile flooring. The layers of floor are; original 3/4" planking, 3/4" plywood, 1/2" cement board, porcelain tile. The tubing is clamped to the underside of the floor with simple pex clamps. I installed 1/2" foam board as insulation. The temp of the water is about 135 degrees which I know is too high but I can't get any heat. I put a thermometer inside the insulation and it reads 130 degrees. Is the floor just too thick to get any heat transfer? Is there a solution to my problem? Any help is appreciated. Bob
 
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  #2  
Old 11-12-08, 04:27 PM
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Seems to me it will take a long while for the heat to penetrate up thru over 2" of wood and concrete -- if ever. I always thought radiant hot water heat piping fit into grooves in special underlayment which you tile directly over.
 
  #3  
Old 11-13-08, 10:11 AM
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Hi Bob, Your cement board and tile are good heat conductors, but the 1 1/2" of wood in between is a good insulator. You need as much contact area as possible, plus a radiant surface directly under the pex or at least directly below the insulation. If your 1/2" foam board has a foil surface. the foil should be facing up. Most installations I have seen have had formed metal plates covering the pex and screwed to the wood.

Increasing the heat is correct, same applies when you have thick carpet (an insulator). The draw back is the increased heat will require more insulation below.

Get a radiant barrier to direct energy towards the wood. Even paint the wood black to increase it's absorption. Although I have no idea as to what paint to use so you are not smelling paint forever. Use metal plates for more thermal conduction. And increase the insulation below to avoid heat loss.

If you want, test a couple of bays before you redo everything. If you haven't, you might want to have a heating guy calculate the BTU's and temp you need to get through that floor.

Good Luck
Bud
 
  #4  
Old 11-18-08, 08:06 PM
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Bud,
Thanks for the advice. I added heat transfer plates to one loop of the floor and used R13 insulation and I got heat. I'm doing the same to the rest of the floor. The added cost is about $600 but with what I have invested in the rest of the system, it's worth it to get the results I wanted.
Bob
 
  #5  
Old 11-19-08, 05:32 AM
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Just so you don't feel bad, I recently worked on a $400,000 class home. Maple floors, sys 2000, every room on it's own zone, a really great job, until you got to the basement. Pex loosely clamped to the floor above and a couple of inches of fiberglass stuffed into the cavities. Just enough so you couldn't see the pex. No radiant barrier, no heat transfer plates, ARGHHH .

Glad it worked out,
Bud
 
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