Enter your heater's output to see the current it draws on a UK supply, compare it with what heater makers state, and know what to ask your electrician.
Short answer: almost every sauna heater needs its own circuit. A 13 A socket supplies about 3 kW, and most garden sauna heaters are 4.5 kW to 9 kW, so they draw 20 A to 40 A on a normal single-phase home supply. The connection is notifiable work under Part P, done by a registered electrician.
Single phase: current = watts ÷ 230. Three phase (balanced): current per phase = watts ÷ (√3 × 400). A 13 A socket supplies about 3 kW. These figures are the heater's own load; your electrician sizes the circuit, cable and protection for your installation.
Calculator by outdoorsauna.uk, using the official rules as checked on 30 September 2026. A guide only, not professional advice: important information.
What supply does a sauna heater need?
The current a heater draws follows from its power. On a UK single-phase supply (230 V), divide the watts by 230: a 6 kW heater draws about 26 A and a 9 kW about 39 A. That’s far more than a 13 A plug and socket can deliver, which is why the heater goes on its own circuit from the consumer unit, like an electric shower.
Heater makers state the fuse each model needs. These are the figures retailers list for heaters that give both single-phase and three-phase requirements:
| Heater | Single phase (230 V) | Three phase (400 V) |
|---|---|---|
| HUUM Drop 4.5 kWas stated by Finnmark Sauna | 1 × 25 A fuse | 3 × 10 A fuse |
| HUUM Cliff 6 kWas stated by Finnmark Sauna | 1 × 32 A fuse | 3 × 10 A fuse |
| HUUM Drop 6 kWas stated by Finnmark Sauna | 1 × 32 A fuse | 3 × 10 A fuse |
| HUUM Hive Mini 6 kWas stated by Finnmark Sauna | 1 × 32 A fuse | 3 × 10 A fuse |
| HUUM Steel 6 kWas stated by Finnmark Sauna | 1 × 32 A fuse | 3 × 10 A fuse |
| HUUM Drop 8.5 kWas stated by Finnmark Sauna | 1 × 40 A fuse | 3 × 16 A fuse |
| HUUM Cliff 9 kWas stated by Finnmark Sauna | 1 × 40 A fuse | 3 × 16 A fuse |
| HUUM Hive Mini 9 kWas stated by Finnmark Sauna | 1 × 40 A fuse | 3 × 16 A fuse |
| HUUM Steel 9 kWas stated by Finnmark Sauna | 1 × 40 A fuse | 3 × 16 A fuse |
| HUUM Cliff 10.5 kWas stated by Finnmark Sauna | 1 × 50 A fuse | 3 × 16 A fuse |
| HUUM Hive Mini 10.5 kWas stated by Finnmark Sauna | 1 × 50 A fuse | 3 × 16 A fuse |
| HUUM Steel 10.5 kWas stated by Finnmark Sauna | 1 × 50 A fuse | 3 × 16 A fuse |
| HUUM Hive 12 kWas stated by Finnmark Sauna | Not possible | 3 × 20 A fuse |
| HUUM Hive 15 kWas stated by Finnmark Sauna | Not possible | 3 × 25 A fuse |
| HUUM Hive 18 kWas stated by Finnmark Sauna | Not possible | 3 × 32 A fuse |
Supply requirements as stated on the retailer's product page. Your electrician will size the cable and protection for your installation; these figures show why a sauna heater needs its own circuit.
Single phase or three phase?
Most UK homes have a single-phase supply. Many sauna heaters can be wired for either, and the bigger ones are three-phase only: the HUUM HIVE at 12 kW, 15 kW and 18 kW, for example. On three phase, the load is shared across the three phases, so the current on each is lower: a 9 kW heater draws about 13 A per phase.
If your home is single phase, choose a heater that can be wired single phase and check the fuse it needs against what your supply and consumer unit can take. That’s the first question to ask your electrician, before you choose the sauna.
What the saunas themselves state
Of the 489 saunas in our data, 124 say what supply they need, and 68 of those mention hardwiring, a dedicated circuit or an electrician. Some outdoor infrared saunas come with a 32 A industrial (“commando”) plug; that still needs a matching outdoor socket on its own circuit. NAPIT’s Codebreakers column looked at one sauna supplied with a plug for a 230 V 32 A industrial socket and raised concerns including exposed live parts, the outdoor IP rating and the lack of emergency switching.
Sources: Professional Electrician: Codebreakers #76 (NAPIT, 22 May 2024). Checked 30 September 2026.
The rules: Part P and BS 7671
In England and Wales, Part P of the building regulations covers electrical work in homes, outbuildings and gardens:
- installing a new circuit is notifiable, and so is replacing a consumer unit;
- a room containing a sauna heater is a special location, where any addition or alteration to a circuit is notifiable;
- Welsh building regulations have differed from England’s since 31 July 2014, so check the Welsh version.
The wiring standard, BS 7671, has a section for rooms and cabins containing sauna heaters (Section 703). A registered electrician works to it, notifies the job and gives you the certificate.
Sources: IET: Part P (England and Wales) - Frequently asked questions; IET Wiring Matters: Protective measures, special installations or locations (Section 703). Checked 30 September 2026.
What to ask your electrician
- Can my incoming supply and consumer unit take this heater’s load, or do I need an upgrade?
- What cable, route and protection will the circuit need, including how it’s buried or run to the garden?
- How will the circuit be protected and earthed?
- Where will the isolator and the heater’s controller go?
- Will you notify the work under Part P and give me the certificate?
Get the quote before you buy the sauna. Steam & Oak’s estimates for the circuit range from £400 to £1,500 (see the cost calculator).
Running cost by heater size
More kilowatts means more current and a bigger bill per hour. At the current price cap, a session costs about £1.97 with a 6 kW heater and £2.96 with a 9 kW, on the assumptions in our running cost calculator. Get the heater size right first with the heater size calculator.
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