About a dollar in July, about two in January.
A sauna heater only draws power while it's on, and at full power a 6 kW heater uses 6 kWh an hour. A session is the heat-up plus however long you stay. Both stretch out in cold weather, so an outdoor sauna's running cost follows the thermometer.
6′ × 6′ barrel, 6 kW, one hour of use
5.9 → 11.8 kWh
About 5.9 kWh on a 68°F day and 11.8 kWh at 0°F. At MG&E's 18.4¢ per kWh, that's $1.09 to $2.17 a session. The U.S. average rate, 18.3¢, works out almost the same.
Estimate · EIA July 2026 rates
kWh and cost per session.
A 6′ × 6′ barrel with a 6 kW heater and a glass door, heated to 176°F and used for an hour. MG&E is Madison's utility. California has the highest average rate in the lower 48.
| Outdoors | kWh per session | MG&E · 18.4¢ | California avg · 33.6¢ |
|---|---|---|---|
| 80°F | 5.1 | $0.94 | $1.71 |
| 68°F | 5.9 | $1.09 | $1.98 |
| 50°F | 7.2 | $1.32 | $2.42 |
| 32°F | 8.6 | $1.58 | $2.89 |
| 20°F | 9.7 | $1.78 | $3.26 |
| 10°F | 10.7 | $1.97 | $3.60 |
| 0°F | 11.8 | $2.17 | $3.97 |
| −10°F | 13.1 | $2.41 | $4.40 |
| −20°F | 14.6 | $2.69 | $4.91 |
Physics estimate, ±20%. Every state's rate is in the calculator below.
Heat-up, then holding.
Heat-up. The heater runs flat out until the thermometer reaches temperature. On a 68°F day that's about 27 minutes for this barrel, or 2.7 kWh. At 0°F it's about 72 minutes, or 7.2 kWh.
Holding. Once it's hot, the controller cycles the heater just enough to replace what leaks out through the walls, glass and vents. On a mild day that's around half the heater's output. In deep cold it can be most of it.
Staying longer costs less than starting. A second hour adds only the holding power, about 3 kWh on a mild day. Two sessions back to back cost less than two separate evenings.
Compared with a hot tub. A hot tub is kept hot around the clock. A sauna uses nothing between sessions. Our cost guide compares a year of each at MG&E rates, and infrared cabins use less again, at the cost of the steam.
Your rate, your weather.
Choose MG&E or any state's average rate, then set how often you'd use it and for how long.
Rated for this room: Harvia KIP-60 (170–300) · HUUM Drop 6 (177–353)
Circuit for a 6 kW heaterFrom the manuals: Harvia KIP-60: 10 AWG · HUUM Drop 6: 30 A breaker, 10 AWG. Your electrician sets the final breaker and wire to code.
Physics estimate, shown as ±20%. It hasn't been checked against measured heat-up times yet. Send yours and help fix that.
Sauna power use.
How much electricity does a sauna use?
At full power, a heater uses its rating every hour: 6 kWh an hour for a 6 kW heater. A whole session, heat-up plus an hour of use, comes to about 6 kWh on a mild day and 12–15 kWh in sub-zero weather for a 6-foot outdoor barrel.
How much does it cost to run a sauna per session?
At MG&E's 18.4¢ per kWh, about $1.10 a session on a 68°F day and about $2.20 at 0°F for a 6-foot barrel with a 6 kW heater. Multiply the kWh by your own rate to compare.
How much does a sauna add to the electric bill each month?
Twice a week, roughly $9–10 a month in summer and $15–20 in a Wisconsin January at MG&E rates, for a 6-foot barrel with a 6 kW heater.
Does a sauna use power when it's off?
No, apart from a Wi-Fi controller on standby. The heater draws nothing between sessions. That's the big difference from a hot tub, which is heated around the clock.
Send us your heat-up time
Note the outdoor temperature and how long the thermometer took. We'll publish the reports together.
- Harvia KIP heaters, 240V single-phase: rated room volumes, amps and supply wire (KIP-30, -45, -60, -80). Harvia KIP-60, Harvia KIP-80
- HUUM Drop heaters, 240V: rated room volumes, amps, breaker and wire (Drop 4.5, 6, 7.5, 9), from published spec sheets. Spec sheet
- Sizing adjustments: HUUM's method multiplies the volume by 1.5 for walls without at least R-13 insulation and adds 3.2 cu ft per sq ft of glass (4.8 if the walls are insulated). Harvia's equivalent: 1.2 m³ per m² of glass or uninsulated surface, and a factor of 1.5 for uninsulated log walls. HUUM sizing, Harvia support
- Electricity rates: U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A, residential average by state, July 2026 (preliminary). MG&E residential rate as in our cost guide. EIA
- Heat-up model assumptions (handbook values): 42 mm solid wood walls with conductivity 0.11 W/m·K; framed walls at about R-13; single tempered glass at 5.8 W/m²·K; 6 air changes an hour through the vents; about 3.5 kg of stones per kW of heater; a 10 mm layer of wood (450 kg/m³, 1.7 kJ/kg·K) warming across walls and benches, starting at the outdoor temperature. Shown as ±20%. Not yet checked against measured heat-up times.