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I am putting in a radiant floor.
Over the existing 3/4 wood subfloor, I am installing half inch PEX lines at 9 inch spacing with 3/4 inch spacers or sleepers between the PEX lines. Then the thin foam sheet underlayment and then laminate flooring.
I am going to use the type of aluminum sheet heat spreaders that have a groove for the PEX tubing to sit in.
The spreaders can be installed in two ways:
1) with the groove facing up and the alum sheet extending over the top of the 3/4 spacers just under the finish floor.
2) with the groove facing down, and the alum sheet extending under the 3/4 spacers (between the spacers and the 3/4 subfloor).
I was told that the performance would be about the same with either scheme, but I did a little test, and scheme 1 seems to do a lot better getting floor surface temperatures that are higher. Since the heat is supplied by solar collectors, the lower the water temperature I can use, the more efficient the system.
So, I am inclined to use scheme 1 (with alum spreaders right under the finished floor). My question is: Are there any disadvantages to this scheme, or any reason I should use scheme 2 instead??
I am using PEX-AL-PEX for the tubing, so the expansion rates for the PEX and the spreader plates will be similar.
The alum sheet I am using for the spreaders is 0.019 thick.
Details on the spreader plate test:
Water temp 92F,
Scheme 1: floor surface temp 82F
Scheme 2: floor surface temp 72F