Radiant heat tubing heat transfer plates

[Frank lammers]

I will be installing heat transfer plates for my under floor radiant heat system. If I were to staple up aluminum flashing in uncovered wood spots ie. were loops are and space between plates, would it make my system more efficient.

 

[Jadnashua]

If the plates on those loops (curved say at the end of a run) were not in contact with the floor except maybe at the edges, then no, they'd act more as radiators, letting heat out rather than directing it to the floor above. But, if you were to leave an air gap between the tubing and the aluminum there, it would act as a radiant barrier and reflect heat back up. To be effective, you need at least a 1/2" air gap for a radiant barrier to work. It doesn't have to be solid aluminum...foil covered craft paper would work as well as a radiant barrier made of solid material. And, you could use that all over underneath the plates (we're talking staple up, not embedded here?) to act as a secondary boost to try to keep the heat contained.

I used that foil-faced craft paper radiant barrier in my attic underneath the roof rafters, and the attic had an immediate 20-30 degree cooling effect, making the a/c more efficient.

 

[Sponsor]

 

[Dana]

The average temperture of the tubing in most under-floor radiant system is quite a bit lower than peak attic roof deck tempertures and the total radiating surface area of the tubing isn't much, so don't infer too much from an attic radiant barrier performance measurement.

Installing the flashing between the tubing and subfloor reflects the heat away, and doesn't increase the surface contact area with the tubing for conducting heat from the tubing to the subfloor. While you could get a (barely measurable with the best instrumentation) improvement with radiant barrier an inch or two below the tubing, shiny aluminum foil would do it as well or better than re-used aluminium flashing, and it would be easier than installing flashing too. If so inclined, tape up some aluminum foil snug to the tubing before adding fiber batt insulation snugged all the way to the top. The gap between the foil & subfloor by the 3/4"-1" o.d. of the tubing will provide another ~ R2 of insulation value at that point and even out the floor temperatures there a bit.

Install fiber insulation snug to the bottom of the heat transfer plates too. Some folks seem all ga-ga about saving a few cents per square foot and installing radiant barrier with a gap instead, but it takes longer to install, and is somewhat lower performance than crummy low-density R19s installed tight to the plates & tubing.

 

[Jadnashua]

Under floor verses embedded radiant often needs to be run at higher temperatures than when it is embedded in the floor. Insulation is good, though!