Sauna electrical requirements, by heater size
Every common heater size, its actual draw, and the breaker the code's 125% rule points at. Computed from rated kW — because almost no manufacturer publishes it.
Last verified · Ice & Cedar editorial
A 6kW sauna heater at 240V draws 25 amps. Because the National Electrical Code treats a sauna heater as a continuous load, the circuit is sized at 125% of that — 31.3 amps — which points at a 35A dedicated breaker. Every common heater size is worked through below.
We are not electricians.The arithmetic on this page is correct and the code references are cited and linked. Your installation is still governed by your local authority having jurisdiction, by the manufacturer’s listed instructions (which take precedence under NEC 110.3(B)), and by a licensed electrician. Use this to know what to ask for — not as a wiring plan.
Heater size to circuit, at 240V
Draw is rated power divided by voltage. Required ampacity is that draw × 1.25. The breaker column is the smallest standard rating (NEC 240.6(A)) that meets it.
| Heater | Draw at 240V | Required (×1.25) | Breaker | Room (approx) |
|---|---|---|---|---|
| 3 kW | 12.5A | 15.6A | 20A | 150 cu.ft |
| 4.5 kW | 18.8A | 23.4A | 25A | 225 cu.ft |
| 6 kW | 25.0A | 31.3A | 35A | 300 cu.ft |
| 8 kW | 33.3A | 41.7A | 45A | 400 cu.ft |
| 9 kW | 37.5A | 46.9A | 50A | 450 cu.ft |
| 10.5 kW | 43.8A | 54.7A | 60A | 525 cu.ft |
Room volumes are the ~50 cu.ft-per-kW rule of thumb, corroborated by manufacturer fit ranges — not a code figure. All rows assume 240V single phase.
Why 25 amps needs more than a 25 amp breaker
This is the part that surprises people, and it is the reason this page exists.
The NEC defines a continuous load as one where the maximum current is expected to continue for three hours or more. A sauna heater sitting at temperature for an evening qualifies comfortably. For continuous loads, NEC 210.19(A)(1)(a) requires branch-circuit conductors to have an ampacity of not less than the noncontinuous load plus 125 percent of the continuous load, and NEC 424.3(B)applies that directly to fixed electric space-heating equipment — confirming that such equipment is treated as continuous.
The reason is thermal, not bureaucratic: sustained current heats the overcurrent device, and that heat migrates into the adjacent conductors. Sizing 25% above the draw is what keeps a breaker that is legally carrying its rated current from cooking the wiring around it. The equivalent framing electricians use: load a circuit to no more than 80% of its rating — the same rule from the other end.
Where the table stops and your electrician starts
Three things this page deliberately does not do:
- Wire gauge. Ampacity depends on conductor material, insulation temperature rating, ambient temperature, bundling and run length. Publishing a gauge table we cannot verify to primary text for your installation would be a safety claim we have no standing to make.
- A confident GFCI answer. NEC 210.8(F) (2023) requires GFCI protection for outdoor outlets on single-phase circuits rated 150V or less to ground and 50A or less. Whether and how that lands on a hardwired outdoor sauna heater is genuinely debated among licensed electricians, and some manufacturers state their own position because certain elements nuisance-trip GFCIs. We are not going to resolve that for you from here.
- Override the manufacturer.Under NEC 110.3(B), listed equipment must be installed per its instructions. Where the manual and this table disagree, the manual wins — and the disagreement is worth a conversation with your electrician.
What this means when you’re shopping
Read the kW rating as a budget item, not a feature. The jump from a 6kW to a 9kW heater is about $40 of hardware and a materially different circuit — 31.3A of required ampacity against 46.9A. If your panel has room for one and not the other, that decides your room size before you have chosen a sauna.
It cuts the other way too: an infrared cabin like the Albott we compare draws 2850W at 240V/20A — less than half the circuit of a 6kW traditional heater. If your panel is the constraint, that is the trade you are actually being offered.
Frequently asked questions
What size breaker does a 6kW sauna heater need?
6kW at 240V draws 25.0A. The NEC treats a sauna heater as a continuous load, so the circuit is sized at 125% of that — 31.3A — and the smallest standard breaker rating that satisfies it is 35A. Two caveats that matter: many manufacturers specify 30A for a 6kW heater, and where the equipment is listed, its installation instructions govern under NEC 110.3(B). Your electrician resolves this against the actual nameplate.
What is the NEC 125% rule?
A continuous load is one where the maximum current is expected to continue for three hours or more. NEC 210.19(A)(1)(a) requires branch-circuit conductors to have an ampacity of not less than the noncontinuous load plus 125 percent of the continuous load. NEC 424.3(B) applies this specifically to fixed electric space-heating equipment — which is what a sauna heater is — and confirms such equipment is treated as a continuous load. In plain terms: the circuit must be sized 25% above the actual draw, because sustained current heats the breaker and the conductors.
Does a sauna need a dedicated circuit?
Yes. A sauna heater draws 25-50 amps continuously for hours at a time; nothing else shares that circuit. This is standard practice and standard manufacturer instruction. Confirm the specifics with your local authority having jurisdiction — local amendments exist and they govern.
Does a sauna heater need GFCI protection?
Possibly, and we are deliberately not going to give you a confident yes or no. NEC 210.8(F) (2023) requires GFCI protection for outdoor outlets on single-phase branch circuits rated 150V or less to ground and 50A or less, which a 240V sauna circuit can fall within. But the exceptions, and whether a hardwired heater counts as an 'outlet' for this purpose, are actively debated among licensed electricians — and some heater manufacturers state their own position because certain elements nuisance-trip GFCIs. This one genuinely goes to your AHJ and your electrician.
What wire gauge do I need for a sauna heater?
We don't publish wire gauge, on purpose. Ampacity depends on conductor material, insulation temperature rating, ambient temperature, how the conductors are bundled and the run length. A gauge table we cannot verify against primary code text for your specific installation is a safety claim we have no business making. Your electrician sizes the conductor; this page tells you the load they are sizing it for.
Can I install a sauna circuit myself?
We are not electricians and this is not an electrical design service, so we are not going to tell you yes. In most jurisdictions a new 240V dedicated circuit requires a licensed electrician and a permit. What this page is for is knowing what to ask for, and knowing when a quote sounds wrong.
Why doesn't the manufacturer just print the amperage?
We don't know, and we won't speculate about motive. The fact is what matters: of every sauna and heater listing we surveyed on 16 July 2026, exactly one published an amperage figure. The draw is fully derivable from kW and voltage, so nothing is being hidden — it is just left to the buyer, who typically discovers it when the electrician arrives.
Related
Sources
- NEC 210.19(A)(1)(a) — minimum branch-circuit conductor ampacity — 2020 NEC. Conductors sized at noncontinuous load plus 125% of the continuous load. (accessed 2026-07-16)
- NEC 424.3(B) — fixed electric space-heating equipment — Space-heating equipment is a continuous load; conductors and overcurrent devices sized at 125% of the heating load. (accessed 2026-07-16)
- NEC 210.8(F) — GFCI protection for outdoor outlets (2023 NEC) — Applies to outdoor outlets on single-phase circuits 150V-or-less to ground and 50A-or-less. Exceptions apply; confirm with your AHJ. (accessed 2026-07-16)