The Sauna Co.Design yoursSheet 406 · Guide
What does a garden sauna cost to run?
Put in the heater and how you use it. Every kilowatt-hour is priced at Ofgem's current cap, the quarter it applies to is printed under the result, and the one assumption in the sum sits on a slider so you can see what it does. Electricity only: a stove that burns wood gets words here, not a number.
406.1 · The calculator
Your heater, your sessions, this quarter's rate
The figure changes as you type. Warm-up is the time the heater runs flat out before the room is up to heat; the session is the time in use after that. The share drawn once hot is the only assumption in the sum, and it is set out in 406.3: move the slider and watch what it does to the year.
406.2 · The sum
How the number is made
A heater draws at most its rating. Until the room reaches temperature it runs flat out, so the warm-up uses the rating multiplied by the warm-up time. Once the thermostat starts to cycle it draws a share of the rating, so the session uses the rating, multiplied by the session time, multiplied by that share. Add the two and you have the kilowatt-hours; multiply by the unit rate and you have the cost.
The unit rate is Ofgem's price cap for 1 October to 31 December 2026: 26.32p a kilowatt-hour, the Great Britain average for a customer paying by Direct Debit, read on 26 October 2026. Ofgem notes there is no VAT on electricity from 1 October 2026 to 31 March 2027, so this quarter's figure is not directly comparable with earlier ones. The cap moves every three months, and this sheet is changed when it does. On a fixed tariff, type the rate on your bill into the calculator instead.
The standing charge is left out on purpose. It is 54.83p a day at the same cap, and you pay it whether the sauna runs or not, so it is a cost of having electricity, not of having a sauna.
The sum is for electric heaters and for the heater alone. It does not include the sauna, the circuit to it, lighting or a plunge pump, and it cannot see your garden: a glass front, a cold night and a door left open all push the real figure up.
406.3 · The assumptions
What is assumed, and what you can change
- Warm-up runs at full power. A heater draws its rating until the stones and the room reach the set temperature. Forty-five minutes is the default; a cold evening, a bigger room or a glass front take longer, and the field is yours.
- Once hot, the heater draws 60% of its rating, averaged over the session. This is the one assumption in the sum. At temperature a heater cycles on and off under its thermostat. Harvia, the Finnish maker, says its 6 kW heaters use 4 to 5 kWh in the first hour and 3 to 4 kWh in the second, which is 50 to 67% of the rating once hot; Finnmark's guide works on roughly half. Sixty sits inside that range, and the slider runs from 30 to 100 so you can set your own.
- A session is 60 minutes and there are three a week. Both are yours to change; the month and the year follow from them, at 52 weeks a year.
- Nothing is added for lighting, a plunge pump or a heater left on standby. They are small, and they are real, and they belong on your bill rather than in this sum.
406.4 · Wood-fired
If the stove burns wood
A wood-fired stove is paid for by the load, not the meter. What a session costs depends on the stove, the wood, how dry it is, how the fire is run and the evening outside. We have not measured it on our own builds, so there is no figure here; when there is one it will be a measured one. Sheet 403 sets out what a wood-fired stove asks of the sauna and the site, and where the rules come from.
406.5 · Questions
Questions people ask about running costs
How much does it cost to run an electric sauna?
A 6 kW heater, 45 minutes to warm up and an hour in use, comes to about 8.1 kWh, which is £2.13 a session at Ofgem's cap for October to December 2026. Three sessions a week is about £28 a month and £333 a year. Change any of those in the calculator and the figure changes with them.
Does the standing charge count?
No. It is paid every day whether the sauna runs or not, so it belongs to having electricity, not to having a sauna. The calculator prices only the units the heater uses, and says so under the result.
Is a bigger heater dearer to run?
It draws more while it runs flat out, and it brings the room up to heat sooner, so over a session the two partly cancel. The heater is sized to the room, not to the bill; the calculator lets you put two ratings side by side in a few seconds.
Why is there no figure for a wood-fired stove?
Because we have not measured one. Wood is bought by the load, and what a session burns depends on the stove, the wood and the evening. A number we had not measured would be a guess with a pound sign on it.
406.6 · Start from this
See it in your garden first
The running cost is the small number. The sauna, the base and the circuit are the large ones, and they depend on your garden. Send a photograph of it and the studio draws a first design into it, with an indicative price band and the questions a site survey will settle.
Before anything is ordered
Electrical. A garden sauna almost always needs its own electrical supply, and running a new circuit to an outbuilding is notifiable work under Part P of the Building Regulations. It must be carried out by a registered electrician who can certify it, so you receive the proper paperwork. The exact cable run, board capacity, and protection are confirmed on site, not estimated in advance.
Sheet 00 · Yours
Describe your garden
A few plain words is enough. The studio turns them into a first design, and we confirm it on a site visit before anything is built.
- Drawn for one garden and built once, to your space and the way you will use it.
- Designed and built from our Gloucestershire workshop. Installed across England and Wales.
- One team from the first sketch to the last screw, electrics included.