Radiant Floor Loop Length Calculator
In a hydronic radiant floor, warm water circulates through loops of PEX tubing embedded in the floor. The total tubing length depends on the heated area and the spacing between tubing runs, while the number of loops depends on a maximum length per loop (so pressure drop and flow stay manageable). This calculator estimates total tubing, loops needed, and tubing per loop from your inputs.
Radiant loop length formula
In-floor tubing (ft) = area (sq ft) * 12 / spacing (in)
Loops = ceiling( in-floor tubing / max loop length )
Tubing per loop (field) = in-floor tubing / loops
Total tubing = in-floor tubing + (loops * leader allowance)
Tube length per square foot equals 12 divided by spacing in inches (for example, 9 inch spacing uses 12 / 9 = 1.33 feet of tube per square foot). Loops are kept under a maximum length (often 250 to 300 feet for half-inch PEX) so each loop has acceptable flow and pressure drop. Leaders are the runs from the manifold to the heated area.
Worked example
A 300 square foot room at 9 inch spacing: in-floor tubing = 300 times 12 / 9 = 400 feet. With a 300 foot maximum per loop, loops = ceiling(400 / 300) = 2. Each loop carries 200 feet of field tubing. Adding a 20 foot leader per loop gives a total of 400 + 40 = 440 feet of PEX.
Radiant loop design notes
- Common tube spacing is 6 to 12 inches on center; closer spacing gives more even, higher output.
- Half-inch PEX loops are typically held to about 250 to 300 feet maximum to limit pressure drop.
- Leaders (manifold to room runs) add tubing that does not heat the floor; include them in your order.
- Always balance loop lengths so each circuit has similar resistance for even heating.
- Confirm spacing and loop limits against the tubing manufacturer's design guide.
Radiant Floor Loop Length Calculator: frequently asked questions
How much PEX tubing do I need for radiant floor heating?
Multiply the heated area in square feet by 12 and divide by the tube spacing in inches. At 9 inch spacing, a 300 square foot room needs about 400 feet of in-floor tubing, plus leader runs to the manifold.
What is the maximum length of a radiant floor loop?
For half-inch PEX, loops are commonly limited to about 250 to 300 feet so that flow rate and pressure drop stay within range. Three-eighths inch tubing uses shorter loops. This calculator lets you set the maximum loop length.
What tube spacing should I use?
Spacing of 6 to 12 inches on center is typical. Closer spacing (6 inches) gives higher and more even output, useful near exterior walls or in high-loss rooms, while 12 inches suits well-insulated areas. Closer spacing uses more tubing.
Why split the floor into multiple loops?
Keeping each loop under the maximum length controls pressure drop and ensures adequate flow and even temperatures. Several balanced shorter loops heat more uniformly than one very long loop.
Sources and methodology
- U.S. Department of Energy: Radiant Heating.
- Tubing length geometry (12 / spacing feet per square foot) is a fixed derivation; maximum loop length and spacing are user-editable per the tubing manufacturer guide.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.