Heat Transfer Plates for Radiant heat under floor joists
While everyone can agree on certain aspects of radiant heat systems e.g., most of the time PEX tubing is the right choice, there is a lot of divergence of opinion on the use of aluminum heat transfer plates in under joist installations over untreated living space. The closest I've been able to come to a reliable answer is a study done that seems to suggest that they are a good idea (ASHRAE Research Project 1036 "Develop Simplified Methodology to Determine Heat Transfer Design Impacts Associated with Common Installation Alternatives for Radiant Conduit")
They tested 4 setups - permutations of with and without heat transfer plates, and insulation close to the PEX, a bit farther. The study concludes that "The primary result from these four configurations is that the heat transfer plates increase the heat that is transferred to the occupied by space by between 160% and 172%, depending on where the insulation was positioned [below the plates]". their graph makes it look clear that plates make a significant difference showing heat flux of around 23 btus without plates and 46 with i.e., looks like a very good way to use lower heat (lower propane usage in my case)
However i don't think it is conclusive. They used the extruded plates that may be more effective than the thin sheets that staple up, and more importantly they used blue board insulation with no mention of a reflective barrier. I wonder if the same results would occur if they used reflective substance on top of the insulation?
So what do ppl think? Do plates give you enough increase to offset the initial cost?
Thanks in advance.
Posted Jan 4, 2012 10:37 PM ET
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