Key facts
- Home sauna heaters are 240V, single-phase.
- 4.5 kW draws 18.8 A, 6 kW draws 25.0 A, 8 kW draws 33.3 A (Harvia, Almost Heaven, Finnleo manuals).
- Manuals call for copper wire rated 90°C.
- Saunas are not covered by NEC 680.44. Sauna heaters fall under Article 424, and Harvia's manuals say not to use a GFI breaker on the heater.
- 9 kW draws 37.5 A and 10.5 kW draws 43.75 A (Harvia Virta manual).
- Many saunas also need a separate 120V circuit for lights.
Heater size, amps, wire and breaker
| Heater | Amps at 240V | Wire (per maker) | Breaker (per maker) | Source |
|---|---|---|---|---|
| 4.5 kW | 18.8 | #10/2, plus #14/2 control | 30 A double-pole | Harvia KIP manual |
| 6 kW | 25.0 | #10/2 (8/2 over 30 ft) | 30 A double-pole | Harvia, Almost Heaven KIP manuals |
| 8 kW | 33.3 | #8/2 | 40 A double-pole | Harvia KIP; Finnleo Designer manual |
| 9 kW | 37.5 | 8/2 (Harvia Virta); 8 AWG (HUUM DROP) | 45 A (Harvia Virta); 50 A (HUUM DROP) | Harvia Virta manual; HUUM DROP manual |
| 10.5 kW | 43.75 | 6/2 | 50 A | Harvia Virta manual |
Manuals can disagree for the same load: Harvia lists a 45 A breaker for its 9 kW Virta, while HUUM lists 50 A for its 9 kW DROP. Follow the manual for the exact heater you buy.
Why some guides say a bigger breaker
Mike Holt's code commentary explains the NEC 125% continuous-load rule for fixed heating (424.3(B)). Retailer blogs such as The Sauna Place and Restore Suite size breakers at 125% of continuous load. That gives 40 A with 8 AWG for a 6 kW heater and 50 A for 8 kW. Those numbers are higher than the Harvia and Almost Heaven manual figures. We are not going to pick a side on code interpretation. The heater's manual, your electrician and your inspector decide.
GFCI and sauna heaters
GFCI: saunas are not covered by NEC 680.44. Article 680 covers swimming pools, hot tubs, spas, fountains, hydromassage tubs and pool lifts, according to Mike Holt's reproduction of the code text. Some retailer blogs say saunas need GFCI under 680.44. That is wrong. A sauna heater is fixed electric space heating equipment under Article 424, and Harvia's manuals say not to use a GFI breaker on the heater. One exception to know: a plug-in receptacle outdoors or in a damp location may need GFCI under 210.8, which mostly affects plug-in infrared units. Follow your own heater's manual, and your inspector has the final word.
How a sauna heater circuit gets installed
- Choose the heater size from the maker's room volume range.
- Have an electrician check panel capacity and run a load calculation. See how the NEC load math works for a sauna and a cold plunge.
- Pull an electrical permit where required.
- Run the 240V heater circuit, plus a 120V light circuit if needed, in 90°C copper sized for the run length.
- Install the control and heater per the manual, then get the inspection before covering the work.
Related guides
- Rocky Mountain Power time of use with a hot tub or sauna in Utah
- Who can pull the electrical permit for a sauna, hot tub or cold plunge in Chicago, DC, Houston, Dallas and Phoenix
- Does a backyard sauna need a permit? The 200 square foot rule by city
- How many sauna stones do I need, and when to replace them
- Outdoor saunas in rainy climates: wood, foundation, roof and heater sizing
- Backyard sauna permits and electrical in Washington
- Backyard sauna permits and electrical in Oregon and Portland
- Sauna electrical and permits in Las Vegas
- The best home saunas of 2026, ranked by use case
- What size sauna heater do I need?
More buying guides
- The best indoor saunas of 2026
- Barrel vs cabin sauna
- Can you wire your own sauna? Homeowner electrical permits in 9 places
- Sauna permit costs in Seattle and Portland, and placement rules in Minneapolis
Frequently asked questions
What size breaker does a 6 kW sauna heater need?
The Harvia and Almost Heaven KIP manuals list a 6 kW heater at 25 amps on 240V, wired with #10/2 copper (8/2 on runs over 30 feet) on a 30 amp double-pole breaker. Some retailer blogs size it at 40 amps using a 125% continuous-load rule. Follow your heater manual, and let your electrician and inspector make the final call.
What size breaker does an 8 kW sauna heater need?
Manuals from Harvia, Almost Heaven and Finnleo list an 8 kW heater at 33.3 amps on 240V. Harvia and Almost Heaven call for #8/2 copper on a 40 amp double-pole breaker. Retailer blogs that apply a 125% rule suggest 50 amps. The manual for your exact heater, plus your electrician, decides which applies.
How many amps does a 4.5 kW sauna heater draw?
About 18.8 amps at 240V, according to the Harvia and Almost Heaven KIP manuals. Those manuals list #10/2 copper supply wire, a separate #14/2 control wire, and a 30 amp double-pole breaker. A 4.5 kW heater suits smaller rooms, so check the heater maker's room volume range before choosing it for a larger sauna.
Does a sauna heater need a GFCI breaker?
Generally no. NEC Article 680, which includes the 680.44 GFCI rule, covers pools, hot tubs and spas, not saunas. Sauna heaters are fixed electric space heating under Article 424. Harvia's Virta manual says "a GFI breaker should NOT be used," and its KIP manual says the same. A plug-in outdoor receptacle may still need GFCI under 210.8. Your inspector decides.
What wire do sauna heaters require?
The manuals we reviewed call for copper wire rated 90°C. Harvia and Almost Heaven list #10/2 for 4.5 and 6 kW heaters and #8/2 for 8 kW. Finnleo lists 8-2 with ground for its 8 kW Designer heater. Some Finnleo Pure models also need a neutral. Wire size can go up on long runs, so measure the distance to your panel.
Do I need a separate circuit for sauna lights?
Often, yes. Many saunas use 240V for the heater and a separate 120V circuit for lighting. Redwood Outdoors describes its barrel saunas this way. Plan both circuits with your electrician at the same time so one trench or conduit run can carry both to a backyard sauna, which usually saves labor.
Will a sauna heater overload a 100 amp panel?
It can. An 8 to 10.5 kW heater adds a 40 to 60 amp circuit, which is a large share of a 100 amp service. We found no published rule for when a subpanel or service upgrade is required, so this is our guidance rather than a cited fact: ask an electrician for a load calculation before you buy the heater.
Can I wire a sauna heater myself?
Finnleo's manual says installation "must be made by a licensed electrician in accordance with the National Electrical Code." Some states let homeowners do electrical work on a home they own and live in, with a permit, including Washington and Oregon. Even where it is legal, a 240V heater circuit near wood and heat is worth hiring out.
Do I need a permit to wire a sauna?
In most places, yes. Electrical work for a sauna heater usually needs an electrical permit and inspection, even when the sauna structure itself is exempt from a building permit. Rules vary by state and city. See our Washington, Oregon and Las Vegas permit guides, and call your local building department before work starts.
Keep reading
Browse our saunas collection, see all guides, or ask us a question about your project.