Heater sizing
Size the room before you size the heater.
Calculate raw room volume, account for glass or other uninsulated surfaces, and verify the result against the exact manufacturer instructions.
Surface adjustment
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 code rule.
Manufacturers can use different logic. Always use the exact heater manual or calculator for final selection.
Source-linked reference ranges
| 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 |
Reference sample, not a product recommendation or approval for every outdoor installation.