Home energy
Room radiator demand Calculator
Size an indicative radiator output from room volume. This free room radiator demand calculator shows the calculation and its assumptions so you can compare your own figures.
Your results
Size an indicative radiator output from room volume.
Calculated outcomes
- Room Volume M3
- 50 m³
- Required BTUPer Hour
- 6,824.28 BTU/h
Assumptions and estimates
- Method: Heat allowance = room volume × selected watts per cubic metre. Radiators are rounded up. BTU/h = W × 3.41214.
- This is a room-volume estimate, not a building heat-loss design. Use manufacturer output at the actual water and room temperatures.
Useful next steps
- Use Compare options to test an alternative side by side.
- Copy, print or download a record of this calculation when you need one.
Reports open your email app addressed to s@s1.ie with the public page address only. Your inputs are never added.
How the room radiator demand calculation works
Heat allowance = room volume × selected watts per cubic metre. Radiators are rounded up. BTU/h = W × 3.41214.
This is a room-volume estimate, not a building heat-loss design. Use manufacturer output at the actual water and room temperatures.
Using this calculator
- Enter your own figures in the labelled inputs. Keep the currencies, units and time periods consistent.
- Choose any applicable rate profile, pattern or assumption shown for this tool. Open additional inputs when relevant.
- Review required watts and radiator count, then read the stated assumptions and eligibility conditions before using the result.
Worked example
This is a static example using illustrative inputs, not facts about you or today’s date. The displayed eligibility selections and assumptions apply only to this example.
See example inputs
- Room length (m)
- 5
- Room width (m)
- 4
- Ceiling height (m)
- 2.5
- Design allowance (W/m³)
- 40
- Output per radiator at operating temperature (W)
- 1500
- Required Watts
- 2,000 W
- Radiator Count
- 2