PEX Pipe Calculator

How to calculate PEX for radiant floors

Formula: area ÷ spacing (ft) + 20% waste. At 9-inch spacing (0.75 ft) in a 300 sq ft room: 300 ÷ 0.75 = 400 ft of loop. Add 80 ft for manifold runs and connections = 480 ft total. Keep each loop under 300 ft — split larger rooms across multiple loops on a manifold.

PEX pipe calculator FAQ

How do I calculate how much PEX I need for radiant heat?

Divide the room area by the loop spacing (in feet) to get linear footage, then add 20% for connections, manifold runs, and waste. For a 12-inch spacing in a 200 sq ft room: 200 ÷ 1 ft = 200 ft of loop, plus 40 ft extra = 240 ft total.

What is the standard loop spacing for radiant floor heating?

Six to twelve inches is the most common range. Use 6-inch spacing for high-heat-loss areas like garages or slab-on-grade in cold climates. Use 9- to 12-inch spacing for well-insulated slabs or heated subfloors. Wider spacing needs more BTUs from the boiler to compensate.

What size PEX is used for radiant heat?

Half-inch PEX (1/2-in) is standard for radiant floor loops up to about 300 feet. Three-quarter-inch PEX is used for longer runs or higher-volume commercial loops. Domestic plumbing supply lines typically use 3/4-in for mains and 1/2-in for branch lines.

How long can a single PEX radiant loop be?

Keep individual loops under 300 feet for 1/2-in PEX to maintain adequate flow and even heat distribution. Longer loops create excessive pressure drop, leading to cold spots near the end. For large rooms, split the area into multiple loops fed from a manifold.