The hydronic floor system will use aluminum plates to conduct the heat from the hot water to the floor. Many home use gypcrete (concrete) with the tubing embedded in it. We use aluminum spreader plates instead to greatly reduce thermal mass and heat loss through the subfloor.
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A Geothermal Radiant Floor installation:
Roth Radiant Floor Panel System for 3/8" & 1/2" Roth PEX Tubing
Planning & Installation Manual
PowerPoint: Radiant Panel Systems
Roth Web site