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