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Sauna electrical requirements calculator

A sauna heater runs for hours at a time, which makes it a continuous load. The National Electrical Code sizes both the wire and the breaker for a continuous load at 125 percent of its current draw, so a heater pulling 25.0 amps needs a 35 amp circuit rather than the 25 amp one the arithmetic alone suggests. That gap is where most planning goes wrong.

Your circuit

Current draw
25.0 A
Minimum breaker
35 A
Minimum copper wire
8 AWG

When the manufacturer publishes a smaller circuit

Sauna makers routinely specify one standard size below what this page computes: 40 amps for an 8 kW heater, 30 for a 6 kW. That is not necessarily an error. NEC 422 covers appliances, and where a listed appliance is marked with its own branch circuit rating, that marked rating is what the installer follows: the maker tested the assembly and had it listed.

This calculator answers the general question, which is the right answer when nothing is marked. Where the two differ, the item pages on this site print both figures, and the decision belongs to the electrician holding the actual nameplate.

Wire sizes are the 60 degree C copper column of NEC 310.16, the column that governs terminations on ordinary residential breakers, with the NEC 240.4(D) small conductor rule applied on top: 14 AWG is capped at 15 amps and 12 AWG at 20 regardless of what the ampacity table alone would allow.

This is a planning figure. Circuit length, ambient temperature, conduit fill, aluminum conductors and your local amendments all change the answer, and the install has to be signed off by a licensed electrician who has seen the actual run.

Common 240 V circuits at a glance

HeaterDraw at 240 VBreakerCopper wireBreaker at 208 V
3 kW12.5 A20 A12 AWG20 A
4.5 kW18.8 A25 A10 AWG30 A
6 kW25.0 A35 A8 AWG40 A
8 kW33.3 A45 A6 AWG50 A
9 kW37.5 A50 A6 AWG60 A
10.5 kW43.8 A60 A4 AWG70 A
12 kW50.0 A70 A4 AWG80 A

Common 120 V heaters at a glance

Plug in models run on a standard household supply. Note that even at this size the continuous-load rule pushes most of them onto a dedicated 20 amp circuit rather than sharing a general-purpose 15 amp one.

HeaterDraw at 120 VBreakerCopper wire
1.5 kW12.5 A20 A12 AWG
1.8 kW15.0 A20 A12 AWG
2 kW16.7 Aover 20 Anot a 120 V circuit
2.4 kW20.0 Aover 20 Anot a 120 V circuit

Models that run on 120 volts: 120 volt plug in saunas. Most still want a dedicated circuit rather than a shared one, and the boundary is close: at about 1.8 kW the continuous-load rule reaches the 20 amp ceiling of a household circuit, so a 2.4 kW panel is already past it. To size the heater itself first, use the heater sizing calculator.

Sauna electrical questions

What breaker does a 6 kW sauna need?
A 6 kW heater on 240 volts draws 25.0 amps. A sauna is a continuous load, so NEC 210.20(A) sizes the breaker at 125 percent of that, which is 31.3 amps, and the next standard breaker up is 35 amps. The conductor has to carry that too, which puts it at 8 AWG copper.
How do I convert sauna kW to amps?
Amps equal watts divided by volts, so kW times 1,000 divided by the supply voltage. A 9 kW heater at 240 volts is 9,000 divided by 240, or 37.5 amps. That is the draw, not the circuit size: multiply by 1.25 for the continuous-load rule before choosing a breaker, which puts a 9 kW heater on a 50 amp circuit.
Why is the breaker bigger than the heater's amp draw?
Because a sauna runs for hours rather than minutes. The National Electrical Code treats any load running three hours or more as continuous and requires both the conductor and the overcurrent device to be rated at 125 percent of it, so the circuit is not sitting at its own limit for the whole session.
Can a sauna run on a normal household outlet?
Some can. The continuous-load rule puts most of them on a dedicated 20 amp circuit rather than a shared 15 amp one, and it reaches that 20 amp ceiling at about 1.8 kW. Above that the calculation asks for more than a household 120 volt circuit provides, which is why larger heaters are wired at 208 or 240 volts, and why the 2.4 kW infrared cabins that do plug into 120 volts are sold as listed appliances marked for a 20 amp circuit under NEC 422. The 120 volt plug in saunas list shows every model in the catalog whose maker specifies 120 volts and no 240 volt circuit.
What wire size does a sauna heater need?
It follows the breaker, not the heater. The table above uses the 60 degree C copper column of NEC 310.16, which is what 110.14(C)(1)(a) requires on circuits of 100 amps or less unless the terminations are listed for a higher temperature, and on ordinary residential breakers they are not. Longer runs, hot attics, crowded conduit and aluminum conductors all push the size up, so treat these as the floor and have the run assessed before buying wire.

Prices and specifications verified August 22, 2026, and re-checked weekly after that. How these numbers are checked.

Free guide: sizing and budgeting a home sauna

A fill-in worksheet covering room sizing math, the electrical checklist, indoor vs outdoor decisions, a full cost worksheet, and ten questions to ask the dealer.