Underfloor Heating Calculator
Estimate the underfloor heating output a room needs.
Heating output required
1,200W
- In kilowatts
- 1.2 kW
- In BTU
- 4,095 BTU/hr
Typical allowances are around 100 W/m² for a well-insulated room and 150 W/m² for a conservatory.
v1.0 · Reviewed September 2026
How this is worked out
Output required is floor area × the watts per square metre you choose.
Worked example
- 12 m² floor
- 100 W/m²
12 × 100
1,200 W, or 1.2 kW
Assumptions and limits
- Around 100 W/m² suits a well-insulated room and about 150 W/m² a conservatory, but a heat loss calculation is the proper basis.
- Use the heated floor area, not the whole room. Mats and cables are not laid under fitted units, baths or shower trays.
- Floor finish matters. Tile and stone transfer heat well, while thick carpet and underlay limit output and may need a surface temperature limit.