Comparison
6 kW vs 8 kW sauna heater
The two most common home sauna sizes. A 6 kW heater is typically rated for about 180–320 ft³ and an 8 kW heater for about 250–420 ft³. Where they overlap, glass and log walls push you to 8 kW.
Room size each one suits
| 6 kW | 8 kW | |
|---|---|---|
| Typical rated room | 177–318 ft³ (5–9 m³) | 247–424 ft³ (7–12 m³) |
| Current at 240 V | 25 A | 33.3 A |
| Common breaker | 40 A | 50 A |
| 400 V three-phase | 3 × 10 A fuses | 3 × 16 A fuses |
Typical ranges overlap, and every model has its own rating. A glass door or wall counts as extra volume: about 1.2 m³ (42 ft³) for each m² (11 ft²) of glass under the Finnish rule.
Warm-up and cost in common rooms
Insulated indoor rooms with a glass door, heated from 68 °F to 176 °F, one hour inside, electricity at 17 cents per kWh. Times and costs come from the calculator's heat model.
| Room | 6 kW | 8 kW | Recommended |
|---|---|---|---|
| 5 × 5 × 7 ft 175 ft³ + glass door | 48 min · $1.07 | 35 min · $1.04 | 6 kW |
| 6 × 5 × 7 ft 210 ft³ + glass door | 55 min · $1.20 | 40 min · $1.17 | 6 kW |
| 7 × 6 × 7 ft 294 ft³ + glass door | 70 min · $1.52 | 49 min · $1.46 | 8 kW |
| 8 × 6 × 7 ft 336 ft³ + glass door | 78 min · $1.69 | 55 min · $1.61 | 8 kW |
| 8 × 7 × 7 ft 392 ft³ + glass door | 87 min · $1.90 | 61 min · $1.80 | 9 kW |
Which one to pick
- Pick 6 kW for a small, well-insulated room with a wooden door, or when your panel cannot spare a 50 A circuit.
- Pick 8 kW for rooms near the top of the 6 kW range, rooms with glass, or when you want the sauna ready faster. It costs about the same per session.
- Between the two? The bigger one warms faster and does not cost more to run. The only real cost is the larger circuit.
Running cost calculator → · Breaker sizes →