Radiator Sizing Calculator

Summary

Calculate the required radiator output (BTU/hr or watts) for a room based on its dimensions, insulation level, and desired temperature rise.

How it works

1. Enter the room dimensions: length, width, and ceiling height.
2. Select the insulation quality of the room (poor, average, good, or excellent).
3. Choose the room type to apply appropriate heat-loss adjustment factors.
4. Set your desired indoor temperature and the design outdoor temperature.
5. The calculator estimates heat loss through walls, windows, ceiling, and floor.
6. Results show the required radiator output in both BTU/hr and watts with a recommended safety margin.

Use cases

• Size a replacement radiator when upgrading an old heating system.
• Determine the number of radiator sections needed for a room extension.
• Verify that an existing radiator is adequate for a poorly insulated room.
• Compare heat demand between rooms to balance a central heating system.
• Estimate heating requirements for a new build or renovation project.
• Plan underfloor heating zones alongside radiators.

Frequently Asked Questions