Product Focus: Radiant Heating Systems Issue: 9/01 Warmboard is a 4 x 8 T&G structural subfloor panel with a top surface of highly conductive aluminum. Carpenters nail it directly to the floor joists in the manner of conventional platform framing. Its modular pattern of grooves link together to provide an infinite variety of radiant designs. The installer then simply presses standard 1/2" PEX tubing into the groove to complete the panel installation. Warmboard.