Underfloor Heating Output Calculator

About this calculator

The heat a water-based underfloor heating (UFH) system delivers depends on the temperature difference between the circulating water and the room, and on the floor construction — the general relationship, formalized in the EN 1264 standard, is that heat output (W/m²) scales with the mean water temperature minus room temperature (ΔT), with the exact output-per-degree factor depending on pipe spacing, floor covering and screed depth. A screeded system with tile flooring and tight pipe spacing delivers noticeably more watts per square metre at the same ΔT than one under thick carpet with wide spacing, because floor covering resistance limits how fast heat can pass through.

Heating engineers and self-builders use output calculations like this to check whether a proposed UFH design can actually meet a room’s heat loss on the coldest day of the year — undersizing pipe spacing or running water too cool relative to floor covering resistance is one of the most common reasons UFH systems feel inadequate in practice, especially in rooms with high heat loss like those with large windows.

This calculator takes your floor area, flow and return water temperatures and room temperature, and estimates the heat output your underfloor heating system can deliver.