Electric heaters: power and circuits
Electric heaters for U.S. outdoor saunas typically run on 240 V single-phase, 60 Hz. The maker publishes a minimum fuse size and supply cable for each model. Two examples from one maker:
| Heater | Voltage | Minimum fuse (one circuit) | If split into two groups | Supply cable | Room volume |
|---|---|---|---|---|---|
| 6 kW | 240 V | 25 A | 16.7 A per group | 10 AWG | 169 to 300 cu ft |
| 8 kW | 240 V | 33.4 A | 22.3 A per group | 8 AWG | 251 to 424 cu ft |
Sources: Harvia Kip60B and Harvia Kip80B. The amps match the math: 6,000 W divided by 240 V is 25 A, and 8,000 W divided by 240 V is 33.3 A.
"Minimum fuse" is the floor, not a finished breaker choice. Your electrician picks the breaker and wire size for your run length, conduit, and panel, and that call can differ from the table. Always read the manual for your exact heater. The product pages say to check the manual for updated information before use.
Check your panel's spare capacity before you choose a heater. A 33.4 A minimum circuit is a large new load on a small service.
Heat-up time
Harvia's energy guidance says a heater runs at full capacity for the first 30 to 40 minutes, depending on sauna size, insulation, and the temperature you set (Harvia energy FAQ). After that, it uses less than half of maximum power to hold the temperature. Harvia also says outdoor saunas need a higher-capacity heater to offset heat loss (Harvia wood-burning guide).
We found no sourced heat-up time for wood-burning sauna stoves, so we do not give one. Ask the stove maker for a time at your room volume.
Clearances
Electric heaters list distances to walls and ceiling in the manual.
- The 6 kW heater above lists 2 inches front and sides, 3.5 feet to the ceiling, and 2 inches to the floor on single-phase.
- A larger wall-mounted 8 kW heater from the same maker lists 3 inches to the sides and 3.67 feet to the ceiling (Harvia The Wall SW80).
Wood-burning stoves need much more room and a flue. A Maine State Fire Marshal guide, based on the 1996 edition of NFPA 211, gives these minimums for unlisted, unprotected stoves (Maine installation guide):
| Stove type | Ceiling | Front | Side | Rear |
|---|---|---|---|---|
| Radiant | 36 in | 36 in | 36 in | 36 in |
| Circulating | 36 in | 24 in | 12 in | 12 in |
Listed stoves, which includes sauna stoves sold with a listing, must be installed to the maker's instructions, and the guide says so. Treat the table as a reference for how far unlisted stoves sit from walls. The guide is old, so use your stove's manual and the code your city adopted.
The same guide also gives these chimney rules:
- The connector must stay at least three times its own diameter from combustible material, unless it is protected.
- Keep the connector short and straight, with no more than two right-angle bends.
- The chimney should rise at least two feet above any part of the building within ten feet.
- Do not run the connector through a closet.
Harvia adds that a sauna chimney must follow local building codes, which can set height, materials, and clearance, and some regions have emission rules (Harvia wood-burning guide).
Permits
Rules differ by city and county. Two sourced points:
- A California city's list of permit-exempt electrical work covers minor items such as replacing a breaker with the same rating. A new 240 V heater circuit is not on that list (City of Beaumont, CA). Assume a new circuit needs a permit and inspection until your city says otherwise.
- Maine's guide tells owners to check with the local fire department or building inspector before installing a wood-burning appliance, and to ask their insurance company about restrictions (Maine installation guide).
Wood-burning also raises site questions that a plug-in heater does not: burn bans, HOA rules, and distance to trees. Call your city and your HOA before you buy.
How to estimate electric running cost
Harvia states that heater kW multiplied by runtime does not directly give kWh, because the thermostat cycles the elements. Use two stages instead.
Formula
- Full-power hours: about 0.5 to 0.67 (30 to 40 minutes).
- Hold hours: session length minus full-power hours, at no more than half of the heater's rating.
- kWh = (kW x full-power hours) + (0.5 x kW x hold hours).
- Cost = kWh x your price per kWh.
This is our method built on Harvia's two statements, and it gives an upper bound.
Worked example. A 6 kW heater, a two-hour session, 40 minutes at full power:
- Full power: 6 kW x 0.67 h = 4.0 kWh
- Hold: 0.5 x 6 kW x 1.33 h = 4.0 kWh
- Total: about 8 kWh
Harvia's own figure for a 6 kW heater in an insulated family sauna is 7 to 9 kWh for a two-hour session, so the method lands in range (Harvia energy FAQ).
The U.S. average residential electricity price was 18.16 cents per kWh in August 2026, up from 17.57 cents in August 2025. These are EIA figures, and the 2026 value is preliminary (EIA Electric Power Monthly). Your bill may differ a lot, so swap in your own rate.
- One session: 8 kWh x $0.1816 = about $1.45. The 7 to 9 kWh range gives $1.27 to $1.63.
- A year at three two-hour sessions a week: Harvia's 1,092 to 1,404 kWh comes to about $198 to $255.
These figures are for an insulated sauna with a right-sized heater. An outdoor sauna loses more heat, so expect to land above them in cold weather.
Wood-burning running cost
Use the same shape: fuel used per session x price per unit of fuel. We found no sourced fuel use per session, so measure your own. Weigh or count the logs you burn over a few sessions, then multiply by what you pay per cord or bundle.
Which fits you
Pick electric if you have panel capacity and want a heater that starts with one switch. Pick wood-burning if your site allows a chimney and open flame, and you have no 240 V service at the sauna. Either way, get the permit answer and the heater manual before you order.