Sauna Heater kW Calculator
Get a correctly sized heater in under a minute. Adjust dimensions, glass and stone — we work out effective volume, fuse rating and recommended power.
Dimensions and materials
How the calculator works
The rule of thumb is 1 kW per cubic metre of sauna volume. We compute volume from your dimensions (assuming a 2.1 m ceiling) and add a heat-loss penalty for glass and exposed stone. The result is rounded up to the next standard heater size (4.5 / 6 / 6.8 / 8 / 9 / 10.5 kW).
How many kW does my sauna heater need?
Use 1 kW per m³ of sauna volume as a baseline. A 2.5 × 2.5 m sauna with a 2.1 m ceiling (≈ 13 m³) usually fits an 8 kW heater. Add another 1.5 m³ per m² of glass door or exposed stone wall.
Why does glass increase the power needed?
Glass has a U-value around 1.1–1.4 W/m²K, versus around 0.2 for an insulated sauna wall. That means a glass door loses 5–7× as much heat as the equivalent timber surface. We compensate by adding 1.5 m³ of effective volume per m² of glass.
What fuse rating is needed?
Heaters up to about 6 kW work on 10 A three-phase. 6.8–9 kW needs 16 A three-phase. Larger heaters (≥ 10.5 kW) may need 20 A. Final installation must always be done by a licensed electrician.