How Much Does a Gas Sauna Cost to Run? Gas Bottles, Refills & Real Per-Session Cost (2026)
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Here's the straight answer, before the detail: a FinSteam gas sauna costs about £2 to £2.50 a session to run on an economy 13 kg gas bottle, or nearer £3 on a small, portable 6 kg bottle. That's roughly level with a big electric heater and in the same band as wood — gas is not the cheapest fuel to run, and anyone telling you it'll slash your energy bill is selling you something.
You buy a gas sauna for what it removes — the electrician, the wiring, the wall socket, the smoke and the fire-tending — not to save on fuel. This guide shows exactly what the running cost is, which gas bottle to choose, and how the buy-versus-refill maths works, so there are no surprises after you buy.
What a session actually costs
The FinSteam Botnia and Aurora heaters are 8.1 kW and burn about 0.59 kg of propane per hour at full output. A gas sauna heater runs near full to hold temperature, so a typical hour-long session — heat up in about 15 minutes, then use it — burns roughly 0.6 kg. A quick session is nearer 0.45 kg; a long, sociable 90-minute session 0.8 kg or more.
The cost of that gas depends entirely on which bottle you refill it from:
| Gas bottle | Refill price (gas only) | Price per kg | Typical session (~0.6 kg) | Sessions per bottle |
|---|---|---|---|---|
| 13 kg propane (economy) | £47–£55 | ~£3.85 | ~£2–£2.50 | ~20 |
| 6 kg propane (portable) | ~£30 | ~£5.00 | ~£3.00 | ~10 |
| 5 kg patio gas (lightest) | ~£34 | ~£6.80 | ~£4.00 | ~8 |
| 47 kg propane (heavy users) | bulk | ~£3.00 | ~£1.80 | ~75 |
The pattern is simple: the bigger the bottle, the cheaper the gas — but the heavier it is to move. A 13 kg bottle weighs about 28 kg full; a 6 kg bottle about 12 kg. That trade-off is the whole decision, and it depends on how you'll use your sauna.
Which gas bottle should you buy?
If your sauna moves around — a tent you take to the garden, the beach, an event — buy the 6 kg propane bottle. At about 12 kg full it's a genuine one-hand carry, sits neatly beside a portable tent, and is easy to swap. You pay a little more per session (~£3 rather than ~£2), but portability is the point of a tent sauna, and lugging a 28 kg cylinder around defeats it. A lightweight composite bottle (the translucent "Gaslight"-type) is another good portable option if your stockist carries one.
If your sauna stays put in the garden, buy the 13 kg bottle — it's the cheapest everyday gas at about £2–£2.50 a session, and you'll refill it far less often. If you sauna most days, a 47 kg cylinder brings the per-session cost down further still, but it's a static, two-person-to-move item.
Always buy propane, never butane. Butane stops turning into gas near freezing point, so a butane bottle is useless outdoors in a British winter — which is exactly when you'll most want a sauna. Propane keeps working down to about −40°C. FinSteam heaters run on propane at the UK 37 mbar spec, which is why the correct UK regulator and hose kit matters (it's included in every Steam & Oak gas package).
Buy once, then just refill
This is where people get confused, so here it is plainly. The first time you get a bottle you pay a one-off Cylinder Refill Agreement — about £39.99 for a 6 kg bottle or £69.99 for a 13 kg. That's a setup cost, not a running cost, and it isn't a deposit: the cylinder legally stays the property of the gas company, and you get a partial refund if you ever hand it back.
After that, you only ever pay the refill price — you bring your empty bottle to any stockist (garden centre, garage forecourt, hardware shop, B&Q) and swap it for a full one, paying just for the gas. That's why refilling is always cheaper than buying a brand-new full bottle each time: a new bottle bundles that £40–£70 agreement back in. Set the agreement up once and forget about it.
How long does a bottle last?
At a typical 0.6 kg a session, a 13 kg bottle gives you around 20 sessions — about seven weeks at three saunas a week. A portable 6 kg bottle lasts about 10 sessions, so around a month at the same rate. Heavy or social users doing longer sessions will get fewer; a quick solo sauna will stretch it further. A sensible move is to keep a spare bottle so you're never caught mid-session with an empty one — swapping takes a minute.
Gas vs electric vs wood — the honest comparison
On 2026 UK prices, all three fuels land in roughly the same place per session:
| Fuel | Cost per session | What it really changes |
|---|---|---|
| Gas (FinSteam propane) | ~£2–£3 | No electrician, no chimney, hot in ~15 min, goes anywhere |
| Electric (6.8–9 kW) | ~£1.75–£2.00 | Needs a dedicated circuit + Part P electrician (£400–£1,500) |
| Wood-fired | ~£2–£4 | No power, but fire-tending, smoke, ash and firewood storage |
The fuel you choose barely moves your energy bill. What it changes is how you install the sauna, where you can put it, and how much faff each session involves. Gas wins on convenience and placement — no wiring, no chimney, no fire to tend, and it's hot in about fifteen minutes — which is the reason to choose it. The running cost is a wash. Full workings for all three fuels here.
The bottom line
Budget about £2–£2.50 a session on a 13 kg bottle, or ~£3 on a portable 6 kg, plus a one-off £40–£70 to set the bottle up. It's a few pounds a sauna — competitive with electric, cheaper than a gym, and the marginal cost of one more session is pence. If the freedom to put a real sauna anywhere, with no electrician and no smoke, is worth a pound or so a session over electric, gas is your answer. If pure fuel cost is your only concern, it's a tie — so decide on everything else. See the gas sauna range or browse portable saunas.
FAQ
How much does a gas sauna cost to run per session?
About £2–£2.50 on an economy 13 kg propane bottle, or nearer £3 on a portable 6 kg bottle, for a typical hour-long session. That's roughly level with a big electric heater.
Which gas bottle is best for a portable sauna tent?
A 6 kg propane bottle — about 12 kg full, easy to carry, and it sits neatly beside a tent you move around. A 13 kg bottle is cheaper per session but heavy (~28 kg), better for a sauna that stays put.
How long does a gas bottle last in a sauna?
Around 20 sessions from a 13 kg bottle, or about 10 from a portable 6 kg, at a typical 0.6 kg a session — roughly seven weeks and one month respectively at three saunas a week.
Is it cheaper to buy a gas bottle or refill one?
Refilling. You pay a one-off Cylinder Refill Agreement (£39.99 for a 6 kg, £69.99 for a 13 kg) the first time, then only ever pay for the gas when you swap an empty for a full one. Buying a brand-new full bottle each time re-charges that agreement, so it's always dearer.
Propane or butane for a sauna?
Propane. Butane stops vaporising near freezing, so it fails outdoors in winter — exactly when you'll want the sauna most. FinSteam heaters run on propane at the UK 37 mbar spec with the supplied regulator.
Is a gas sauna cheaper to run than electric?
No. On 2026 UK prices gas is about level with electric, sometimes a touch more. You choose gas for no electrician, no chimney and instant, go-anywhere heat — not to cut your energy bill.
