Radiator size calculator

How it works

Heat demand is room volume times a watts-per-cubic-metre factor for the insulation level. Radiator length assumes a 24 in double-panel (type 22) radiator gives about 1,700 W per metre.

How to measure

Measure floor area and ceiling height. Tick the exterior-walls option for corner rooms.

Tips

• Output depends on water temperature; low-temperature systems need larger radiators.
• Place radiators under windows where possible.
• For an exact size, have a room-by-room heat loss calculation done.