Typical heat-up times (model results)
| Sauna | Heater | Around the sauna | To 80 °C (176 °F) |
|---|---|---|---|
| Indoor 2.0 × 1.8 × 2.1 m, glass door | 6 kW | 20 °C | ≈ 45–50 min |
| Indoor 2.0 × 1.8 × 2.1 m, glass door | 8 kW | 20 °C | ≈ 30–35 min |
| Indoor 1.5 × 1.8 × 2.0 m, wooden door | 4.5 kW | 20 °C | ≈ 55–60 min |
| Barrel 1.8 m (6 ft) × 1.8 m | 6 kW | 5 °C | ≈ 40 min |
| Barrel 1.8 m (6 ft) × 1.8 m | 6 kW | −10 °C | ≈ 50 min |
| Barrel 1.8 m (6 ft) × 2.4 m (8 ft) | 6 kW | −10 °C | ≈ 70 min |
Heater manuals often say a correctly sized heater needs about an hour to bring the room to bathing temperature; well-insulated rooms with a strong heater are faster.
Why the walls matter as much as the heater
The thermostat reads the air at the ceiling, but the air holds very little heat. The stones and the wood lining store most of it: the walls are still warming up long after the air has reached 80 °C, which is why the first half hour of a session feels milder than the second. Glass and solid wood walls take more heat to warm up and lose more of it.
Making it faster
Choose the heater from the upper half of its maker's range, put insulation behind the panels, use a wooden or smaller glass door, and close the vents until the room is hot if the maker allows it.