Joist Trak Panels are manufactured by Uponor Wirsbo. These Wirsbo Joist Trak Radiant Heat panels are made from thick alluminum alloy and provide excellent heat transfer to the space above. They are attached beneath the wood subfloor in Radiant Heat Systems. How many pieces of joist trak do I need? For 8" on-center spacing, multiply the net area to be heated by 1.5. Take the total tubing number and multiply it by .85. Divide this number by four. This will tell you how many Joist Trak Panels you will need. For Example, if we have a room that is 400 sq ft., multiply it by 1.5, you will need 600 feet of tubing assuming 8" on center. you will then need to multiply 600 by .85, which gives you 510. 510 divided by 4 is 127.5. So you will need approximately 128 Joist Trak Panels. When installing Joist Trak, leave 1-2" between panels.