What size PEX Tube / PEX Tubing should you use for your Radiant Heat System?

PEX Tubing comes in several different sizes. The most common sizes of PEX Pipe for Radiant Heat Systems is 3/8 Inch, 1/2 Inch, 5/8 Inch and 3/4 Inch. Generally, for residential Radiant Heat Systems we recommend 1/2 Inch PEX Tubing. The PEX Tube size dictates the flow rate that can be achieved and thus the maximum loop length of the pex tube. 1/2 Inch PEX Tubing accounts for the majority of Residential Radiant Heat installations and should be used in most slab, overpour, or joist underfloor heating applications.

5/8 Inch PEX and 3/4 PEX pipe are generally reserved for large commercial and snow-melt applications. This size PEX piping is also used for supply and return lines.

Size Inside
Diameter (inches)
Outside
Diameter (inches)
Volume in gallons per 100 feet of tubing
3/8" .35 .5 .5
1/2" .475 .625 .92
5/8" .574 .75 1.34
3/4" .671 .875 1.84
1" .862 1.125 3.03
*This table does not apply to PEX-AL-PEX Alumimun Tubing

 

Maximum PEX Tubing Run Lenghts

3/8 inch PEX Pipe Loops should not be over 200 feet

1/2 inch PEX Pipe Loops should not be over 300 feet

5/8 inch PEX Pipe Loops should not be over 400 feet

3/4 inch PEX Pipe Loops should not be over 500 feet