Calculate raw room volume, then account for glass or other uninsulated surfaces before comparing the result with the current heater manufacturer’s rated room-volume range.
This planning calculator uses 3.3 ft³ of added effective volume per ft² of uninsulated surface, the imperial form of a 1 m³-per-m² approach published in sauna-heater guidance. It is not a universal building code.
Different heater manufacturers may use different sizing logic. Always use the specific heater’s current manual/calculator for final selection.
| Brand | Model | Output | Rated room volume | Source |
|---|---|---|---|---|
| Harvia | Cilindro PC70 | 6.8 kW | 212–353 ft³ | manufacturer source |
| Harvia | Cilindro PC90 | 9.0 kW | 283–494 ft³ | manufacturer source |
| Harvia | Cilindro PC110EE | 11.0 kW | 318–636 ft³ | manufacturer source |
Small reference sample only; not a recommendation that these specific heaters are appropriate for an outdoor installation.