Underfloor Heating Output Calculator

Work out underfloor heating output instantly with clear inputs, formula shown and shareable results.

About Underfloor Heating Output Calculator

Underfloor heating output rises with the difference between mean water temperature and room temperature, scaled by how easily the floor finish conducts heat upward. Tile passes heat well, carpet resists it. Output per square metre is capped at 175 W/m² because the floor surface temperature limit, not the water temperature, sets the practical ceiling.

Formulas

Floor output

W/m² = covering coefficient x 11 x (mean water temp - room temp), capped at 175 W/m²

Surface temperature

Surface °C = room °C + (W/m²) / 11

Worked example

With the default values below, Underfloor Heating Output Calculator returns Total floor output of 3,500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Heated floor areaminimum 1 m²: 20 m²
Mean water temperatureminimum 20 °C: 40 °C
Room design temperatureminimum 5 °C: 21 °C
Floor coveringone of Tile or stone, Engineered wood or laminate, Carpet with underlay: Tile or stone

Results

Total floor output: 3,500 W
Output per square metre: 175.0 W/m²
Water-to-room difference: 19.0 K
Estimated surface temperature: 36.9 °C

Step by step

1Values used
2Floor output
3Surface temperature
4Total floor output= 3,500 W
5Output per square metre= 175.0 W/m²
6Water-to-room difference= 19.0 K
7Estimated surface temperature= 36.9 °C

Assumptions and limits

The result is derived only from the 4 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 1 decimal place, 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 the Underfloor Heating Output figure worked out?

W/m² = covering coefficient x 11 x (mean water temp - room temp), capped at 175 W/m². Underfloor heating output rises with the difference between mean water temperature and room temperature, scaled by how easily the floor finish conducts heat upward.

What surface temperature is acceptable?

Occupied areas are normally limited to about 29 °C and perimeter zones to 35 °C. If the calculated surface temperature exceeds that, extra emitters or better insulation are needed rather than hotter water.

What values do I need to enter?

This calculator takes 4 inputs: Heated floor area, Mean water temperature, Room design temperature, Floor covering. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.