Max. Loop Lengths for Radiant Heat

A “loop” or “circuit” in a radiant heat system refers to a single run of tubing and its length before it returns to the manifold. Due to flow restriction and heat loss, each loop must be sized so that it can provide adequate flow of hot water to heat the space before water temperatures drop too much. The maximum recommended loop lengths listed below are not necessarily hard and fast rules. They can be exceeded, but doing so would likely require a circulator pump that is either quite costly or does not exist. When calculating loop lengths, always be sure to create loops that minimize materials costs while providing adequate heat. This includes matching the total amount of PEX tubing needed with the roll sizes offered by manufacturers. Keep in mind that a certain amount of tubing will also be needed between the heated space and manifolds. Known as the "leader length," this must be included in the overall loop length.

5/16” – *250 feet
3/8” – 240 feet
1/2” – 300 feet
5/8” – 330 feet
3/4” – 400 feet

*longer because it's based on 20°F Delta-T for Uponor Quik Trak (all other sizes based on 10°F Delta-T)