Radiant Floor Heat Calculator
Calculate tubing length, loop count and output for underfloor heating.
About Radiant Floor Heat Calculator
Tubing length is the area divided by spacing, with an allowance for the run back to the manifold. Loop length is capped by pressure drop, which is what determines how many manifold ports are needed. Floor covering can cut output by 40 per cent, so specifying carpet after sizing the system for tile leaves the room permanently short of heat.
Formula
Radiant Floor Heat
Tubing length = area ÷ spacing, plus an allowance for returns to the manifold
- spacing
- Centre distance between tube runs, typically 150 to 300 mm
- covering derate
- Carpet and wood insulate the floor, reducing output
Worked example
With the default values below, Radiant Floor Heat Calculator returns Tubing Length Required of 247.5. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Heated floor areaminimum 0.1 m2
- 45 m2
- Tube spacingminimum 50 mm
- 200 mm
- Maximum loop lengthminimum 10 m
- 100 m
- Heat outputminimum 10 W/m2
- 70 W/m2
- Floor coveringone of Tile or stone, Engineered wood, Carpet, Vinyl
- Tile or stone
Results
- Tubing Length Required
- 247.5 m
- Loops Required
- 3
- Manifold Ports Needed
- 3
- Total Heat Output
- 3,150 W
- Output After Floor Covering Derate
- 70.00 W/m2
Step by step
- 1Values used
- 2Radiant Floor Heat
- 3Tubing Length Required= 247.5 m
- 4Loops Required= 3
- 5Manifold Ports Needed= 3
- 6Total Heat Output= 3,150 W
- 7Output After Floor Covering Derate= 70.00 W/m2
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Radiant Floor Heat calculated?
Tubing length = area ÷ spacing, plus an allowance for returns to the manifold Tubing length is the area divided by spacing, with an allowance for the run back to the manifold. Loop length is capped by pressure drop, which is what determines how many manifold ports are needed.
Why does Radiant Floor Heat matter?
Floor covering can cut output by 40 per cent, so specifying carpet after sizing the system for tile leaves the room permanently short of heat.
What values do I need to enter?
This calculator takes 5 inputs: Heated floor area, Tube spacing, Maximum loop length, Heat output, Floor covering. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.