Sauna electrical requirements in the UK

How many amps a sauna heater draws

On a normal single-phase UK supply, a heater's current in amps is its power in kW × 1,000 ÷ 230. A 6kW heater is 6,000 ÷ 230 = 26.1A, twice what a 13A plug is rated for, and it keeps drawing that for the full hour the room takes to heat.

The fuse and room figures are from Harvia's spec pages for its Vega heaters: 3.5kW, 6kW, 8kW and 9kW. Other makers' heaters of the same output draw the same current, because the sum depends only on power and voltage.

Three-phase wiring splits the load across 3 smaller fuses, but it only helps if your property already has a three-phase supply. If you're not sure which you have, your electrician can confirm it on the first visit.

What circuit a 3.5kW to 9kW sauna heater needs

Every electric sauna heater from 3.5kW up needs its own dedicated circuit from the consumer unit. Even the smallest draws more than the 13A a standard plug is rated for, so none of them plugs in.

Sellers quote supplies of 32A to 50A for 6kW to 9kW heaters, but the final breaker and cable are your electrician's call, made from the heater's installation instructions, the length of the run and how the cable is installed. Long runs to the bottom of the garden often need a thicker cable than a short run indoors, to keep the voltage drop within limits.

Before any of that, the electrician checks whether the house can take the extra load. That means looking at the main fuse rating and what else runs at the same time, such as an electric shower, an oven or a car charger. A 9kW heater adds about 39A on top, which an older or smaller supply may not have room for.

Heater size drives the circuit far more than brand does, so compare the supply each of the best electric sauna heaters needs before you compare their prices. Dropping from 9kW to 6kW takes about 13A off the circuit.

Part P: notifiable sauna electrical work in England

In England, regulation 12(6A) of the Building Regulations 2010 makes 3 kinds of electrical work notifiable: installing a new circuit, replacing a consumer unit, and adding to or altering circuits in a special location. The same regulation lists "a room containing a swimming pool or sauna heater" as a special location.

A sauna heater on its own circuit is therefore notifiable on 2 counts, and so is any later change to the wiring in the sauna room. A new consumer unit, if your old one has no spare way or can't take the load, is notifiable too.

A garden sauna small enough to be exempt from the Building Regulations doesn't escape this. Regulation 9 keeps Part P in force for small detached buildings that take their electricity from the house, and Approved Document P names outbuildings such as sheds and detached garages as within its scope.

In practice the first route is the simplest: hire an electrician registered with one of the government-authorised competent person schemes, and the certificate and notification come with the job.

Sauna electrics in Wales and Scotland

Wales casts the net wider. Its Approved Document P for Wales lists hot air saunas as a special location and outdoor lighting and power as a special installation, and says any new work in the garden, or that involves crossing it, is notifiable. Adding a socket to an outside wall is notifiable too, and the document notes it needs RCD protection.

So in Wales, even extending an existing circuit to a garden sauna is notifiable, where in England only a new circuit or work in the sauna room itself would be. There, a Part P registered installer issues the compliance certificate, or an unregistered one notifies building control before work starts.

Scotland has no Part P. Under regulation 5 of the Building (Scotland) Regulations 2004, work listed in schedule 3, which includes most work to or in a house, needs no building warrant but must still meet the building standards. A garden sauna with a wood-burning stove is different, because the outbuilding exemptions exclude buildings with a fixed combustion appliance.

BS 7671 for saunas in plain terms

BS 7671 is the IET Wiring Regulations, the British Standard every installation is designed, installed and tested to. Approved Document P says electrical installations should follow it, and that applies to non-notifiable work as much as notifiable work.

Saunas get their own section, Section 703, because heat and moisture change the risks. It follows the international standard for rooms and cabins containing sauna heaters, which treats the whole room as the sauna, divides it into 3 temperature zones and sets extra rules for protection against electric shock. In plain terms, it controls what equipment can sit where around the heater, what it must withstand and how it's protected.

Check the heater maker's instructions on RCDs before the circuit is designed. Harvia's Vega manual tells installers not to feed the heater's power through an RCD, and the same section explains that new elements can absorb moisture in storage and transport, which shows up as leakage until the heater has been used a few times.

Lights, sockets and any outdoor wiring are a separate matter, and your electrician designs RCD protection for the whole installation. At the end you should get a BS 7671 Electrical Installation Certificate, and for notifiable work a Building Regulations compliance or completion certificate as well.

Running power to a garden sauna

The usual way to get a heater circuit to a garden building is steel wire armoured cable, known as SWA, run from the consumer unit to an isolator at the cabin. The steel armour protects the cable from spades, forks and the odd tent peg.

It goes underground in a trench, clipped along a wall or fence, or a mix of both, and the electrician sets the cable size for the full length of the run. If you're building a concrete base, lay a duct through it before the pour, so the cable comes up inside the cabin's footprint instead of across the floor of the garden sauna base.

Plan the run before the cabin arrives. Digging a trench across a lawn is easy before a 600kg cabin and its base are sitting on the route, and much harder after.

Plug-in infrared saunas: 13A plugs and commando sockets

Infrared cabins draw far less than a traditional heater, and some are built to plug in. Clearlight's UK range shows the spread: its 2-person indoor cabin is 2,500W on a 13A UK plug, while its 3-person cabin comes without a plug and must be hard-wired by an electrician.

The outdoor cabins use commando plugs, the round industrial connectors built for outdoor use, on their 2-person and 5-person models. Plug-in doesn't mean no electrician: unless you already have a matching socket outdoors, fitting a 16A or 32A commando socket means a new circuit, which is notifiable in England and Wales.

Clearlight also says that adding its accessories to the 13A cabins can change the electrical requirement, and suggests asking an electrician whether a dedicated circuit is needed. A 2,500W cabin draws about 10.9A, so it should have a socket to itself rather than share an extension lead.

What drives the cost of sauna electrics

Electricians price sauna circuits per job, and the spread between a simple one and a hard one is wide. These are the things that move it, so you can judge a quote and give the electrician what they need to price it first time.

Get the heater model and its installation manual to the electrician before they quote, along with a measured distance from the consumer unit to the cabin. Those 2 things set most of the price.