Radiator & BTU Calculator

Create a rough early-stage heating-load placeholder. Final emitter selection requires room-by-room heat-loss design and manufacturer output data at the actual system temperatures.

How to use the Radiator & BTU Calculator

Enter the room dimensions — length, width, and height.
Select the room type, insulation level, and glazing type.
Indicate the number of external walls and any special factors.
Review the rough planning load, then obtain a room-by-room heat-loss design and exact manufacturer output data.

Why use this tool

Provides an early planning figure from simple room factors.
Accounts for variables that significantly affect heat demand — insulation, glazing, and exposed walls.
Makes the omitted fabric, infiltration and design-temperature checks explicit.

This is not a radiator-sizing or heating-system design result. A real room-by-room heat-loss calculation needs measured fabric areas and U-values, infiltration or ventilation, design temperatures and system operating temperatures. Select equipment only from the exact manufacturer's output at the applicable mean water-to-air temperature difference and have the complete system checked by a competent heating designer.

Part of Builder Tools Calculators — free construction tools for UK tradespeople.