Radiator Sizing Calculator
Determine the right radiator heating output for your room based on area, insulation and ceiling height.
The right heating output depends on room volume and the building's insulation standard. This calculator gives a rough estimate of the required radiator output in watts.
Pro tips
- Corner rooms and rooms with many exterior walls need somewhat more output.
- Hydronic balancing improves the efficiency of existing radiators.
Frequently Asked Questions
How do I calculate the right radiator size?
Roughly: room area × room height × a heat demand factor based on insulation standard (about 30-100 W/m² depending on build year and insulation).
How many watts of heating output does a room need?
With good insulation, 40-60 W/m² is often enough; older, unrenovated buildings can need 100 W/m² or more.
Is an oversized radiator a problem?
A slightly larger radiator is usually fine and can even run more efficiently at lower flow temperatures – but significantly oversizing it isn't worthwhile.
How does insulation affect radiator size?
The better the insulation, the less heating output is needed per square meter – new builds often need much less than older buildings of the same size.