Birch & Berg

Electrics

Sauna and cold plunge electrics: a UK guide

Single or three-phase, 13A plug or dedicated circuit, RCDs, outdoor sockets and Part P in England: what power a garden sauna or cold plunge chiller needs.

By Birch & Berg. Last checked .

Short answer: most traditional electric sauna heaters need their own circuit from your consumer unit. Most cold plunge chillers, and some smaller infrared cabins, run from a 13A socket. Any new circuit, including a new supply to the garden, is notifiable under Part P of the Building Regulations in England, so use a registered electrician. Every product page states the power and supply each model needs. The building rules here are for England; Wales, Scotland and Northern Ireland have their own.

1. Single-phase or three-phase

  • Single-phase is the normal UK home supply, declared at 230 volts.
  • Three-phase is three 230 V supplies together, giving about 400 V between phases (230 × 1.73). It's a different connection, arranged with your local network operator.

Some sauna heaters, particularly those made for European markets, are designed for a three-phase 400 V supply. Most UK homes don't have one. Unless the product page confirms a single-phase 230 V option, ask us before you order. Upgrading to three-phase means applying to your network operator for a quote. It isn't something an electrician can switch over on the day.

2. 13A plug or dedicated circuit

A 13A plug can supply at most about 3 kW (13 A × 230 V = 2,990 W). To see what an appliance draws, divide its power by 230 V:

Example appliancePowerCurrent drawnUsual supply
Cold plunge chiller0.8 kW3.5 A13A socket, if the product page says so
Small infrared cabin2 kW8.7 ASome use a 13A socket; larger cabins need their own circuit
Small traditional heater4.5 kW19.6 ADedicated circuit
Typical barrel sauna heater6 kW26.1 ADedicated circuit
Large cabin or panoramic heater9 kW39.1 ADedicated circuit

The power figures are examples; use the rating on the product page. Anything over about 3 kW can't run from a plug. Even below that, a heater or chiller running for hours is a heavy, steady load:

  • plug it straight into a wall socket;
  • never run it from an extension lead or cable reel (Electrical Safety First advises against powering a heater from an extension lead, because leads are easily overloaded);
  • don't share the socket with other high-power appliances.

3. RCD protection

An RCD (residual current device) switches the power off quickly when it detects current leaking to earth, for example through a damaged cable. The UK wiring regulations (BS 7671) require additional protection by an RCD rated at 30 mA or less for socket-outlets rated up to 32 A, and for mobile equipment used outdoors.

  • Electrical Safety First advises using an RCD with all outdoor electrical equipment.
  • An RCD's "T" or "Test" button should switch off the power to the circuits it protects. Test it as the maker recommends.
  • Rooms and cabins with sauna heaters have their own section in BS 7671 (section 703), with extra requirements. Use an electrician who knows it.

4. Outdoor sockets for chillers

  • The socket must be weatherproof and RCD-protected, positioned so the plug and cable stay clear of water and splashes.
  • Put it close enough that you don't need an extension lead. If you have to use one briefly, it must be outdoor-rated, and a cable reel must be fully unwound.
  • Don't run cables across paths, where they can trip someone or be cut.
  • In England, adding a socket to an existing circuit outside a special location isn't notifiable, but it must still meet BS 7671. Use a qualified electrician.

5. Part P: when the work is notifiable (England)

In England these jobs are notifiable:

  • installing a new circuit, wherever it runs, including a new circuit to a garden building;
  • replacing a consumer unit;
  • any addition or alteration to a circuit in a special location, which includes a room containing a sauna heater.

There are three ways to meet the rules:

  1. A registered electrician (a member of a competent person scheme) does the work and self-certifies it. This is the simplest route.
  2. Building control is notified before work starts, and inspects it.
  3. A registered third-party certifier (England only) is notified before work starts.

With a registered electrician, you should receive an Electrical Installation Certificate when the work is done, and a Building Regulations compliance certificate from their scheme within 30 days. Keep both with your house documents. You can find registered electricians on the electrical competent person register.

Manufacturer warranties usually require electrical work to be done by a qualified electrician, too.

6. Running a sauna and a chiller together

A 6 kW heater and a 0.8 kW chiller running at once draw about 30 A (6,800 W ÷ 230 V), on top of whatever the house is using. Your electrician will check that your supply and consumer unit can take it. For what they cost to run, see our running-cost and chiller guides.

7. What to tell your electrician

  1. The heater's power (kW) and required supply (single or three-phase), from the product page.
  2. The chiller's power, and whether it has a 13A plug or needs hard-wiring.
  3. The distance from your consumer unit to the sauna or plunge, and the cable route. A duct laid before the base goes down makes this easier (see our base guide).
  4. Where you want the socket, isolator and heater controls.
  5. For a wood-fired sauna: there's no heater circuit, but lights or sockets still need an outdoor supply.

Wales, Scotland and Northern Ireland

Building regulations are devolved. In Wales, Part P differs from England: special locations include kitchens and outdoors. Scotland and Northern Ireland have their own building standards. Check with your local building control, or on gov.wales, mygov.scot or nidirect.

FAQs

Can I plug a sauna into a normal socket?
Only some smaller infrared cabins. A traditional heater of 4.5 kW or more draws about 20 A or more, well over what a 13A plug can supply. Each product page states which applies.

Does a cold plunge need its own circuit?
Usually not. Most chillers run from a 13A socket, but check the product page. You need a weatherproof, RCD-protected socket nearby. If there isn't one, or the chiller must be hard-wired, use a qualified electrician.

Can I do the wiring myself?
In England, notifiable DIY work must be reported to building control before you start, and they will inspect it. With heater loads and water nearby, we recommend a registered electrician. We can't give wiring advice for your home.
This is general guidance for England, not electrical advice for your property. Always follow the manufacturer's instructions, and have a registered electrician design and install the supply.

Sources

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