Use this as a starting point for budget and layout. Final selection always accounts for glass area, uninsulated masonry and the design ventilation rate — the worked corrections are set out below the table.
Baseline heater selection
| Cabin volume | Bathers | Heater output | Supply | Typical energy use |
|---|---|---|---|---|
| 4 – 6 m³ | 2 – 3 | 4.5 kW | 230 V / 1 ph | ≈ 3.1 kWh per session |
| 6 – 9 m³ | 3 – 4 | 6.0 kW | 400 V / 3 ph | ≈ 4.2 kWh per session |
| 9 – 13 m³ | 4 – 6 | 8.0 kW | 400 V / 3 ph | ≈ 5.6 kWh per session |
| 13 – 18 m³ | 6 – 8 | 9.0 kW | 400 V / 3 ph | ≈ 6.4 kWh per session |
| 18 – 24 m³ | 8 – 12 | 12.0 kW | 400 V / 3 ph | ≈ 8.5 kWh per session |
| 24 – 35 m³ | 12 – 18 | 15.0 kW | 400 V / 3 ph | ≈ 10.8 kWh per session |
Corrections
- Double glazing: add 1.2 m³ of equivalent volume per m² of glass.
- Single glazing: add 1.8 m³ per m².
- Uninsulated masonry, concrete or tile: add 1.5 m³ per m².
- Ventilation above four air changes per hour: add 10 % to the corrected figure.
Stone bed
Allow 6 kg of split stone per kilowatt of heater output for commercial duty, 4 kg per kilowatt for domestic. Split olivine diabase only — tumbled river stone has a fraction of the effective surface area and gives poor löyly.
Temperature and humidity ranges
| Environment | Temperature | Relative humidity |
|---|---|---|
| Finnish dry sauna | 80 – 100 °C | 10 – 20 % RH |
| Finnish sauna with löyly | 75 – 95 °C | 20 – 35 % RH during löyly |
| Laconium / soft sauna | 55 – 65 °C | 20 – 30 % RH |
| Infrared cabin | 40 – 65 °C | Ambient |
| Steam room | 42 – 48 °C | 95 – 100 % RH |
Ventilation
Inlet low behind or under the heater, outlet high on the diagonally opposite wall. Size for four air changes per hour domestic, six for commercial. The outlet must be open during bathing — closing it to retain heat is the single most common operating mistake and it ruins löyly.
Compliance
- CE / EN 60335-2-53 — electrical safety for sauna heating appliances.
- ETL / UL 875 — North American listing for our electric heater and control range.
- FSC® Chain of Custody — traceable Nordic spruce and aspen.
- IP24 or better — steam room fittings, lighting and sensors.
