Joist Trak™ extruded aluminum heat transfer panels use 3/8 or 1/2 in Uponor PEX in floor joist applications. Each panel is 4 ft x 3-1/2 in and comes packaged 20 per box. They provide easy installation, increased heat transfer and superior comfort. Uponor Joist Trak™ Heat Transfer Panel, 48 in Length, 3-1/2 in Width, Aluminum, Domestic