PEX tubing sizes, circuit lengths and floor output

Factors such as tubing size and circuit length directly represent the heat output (in BTH/sq ft/hr) of the radiant heating system. The later is especially important, since heat loss calculation is the initial stage of every radiant heating project and allow the engineer to determine which tubing size to specify.

Some of the common examples are listed below:

PEX Tubing Size Recommended
Circuit length
Recommended tube spacing (OC) Suggested flow (GPM) Floor output (BTU/sq ft/hr)
3/8" PEX 200ft 6-9" 0.3 22-30
1/2" PEX 300ft 9-12" 0.6 22-30
5/8" PEX 400ft 12-16" 0.9 10-24
3/4" PEX 500ft 12-16" 1.2 17-26

To increase the floor output for selected tubing size and length, the flow needs to be increased.
For example, by increasing the flow through 1/2" PEX tubing by only 0.1 GPM, floor output will increase at 5 BTU/sq ft/hr.

For actual calculations, consult with your radiant system designer.