Wood-Fired Hot Tubs UK: How They Work, What They Cost, and Who Should Buy One

A wood-fired hot tub heats its water with a stove rather than an electric element. No pump, no control panel, no electrician, and nothing running when you are not using it.

That is the whole proposition, and whether it suits you comes down to one question: are you willing to light a fire an hour or two before you get in? If yes, it is dramatically cheaper to own than an electric spa. If no, no amount of romance about flame and steam will fix that.

This guide covers how they actually work, what they really cost, the smoke question that catches people out, and who should buy one.

How a wood-fired hot tub works

Water circulates by convection — no pump involved. Cold water is denser, so it sinks to the bottom of the tub, passes through the stove's heat exchanger, warms, becomes less dense and rises back into the tub. That cycle continues on its own for as long as the fire burns.

You control the temperature by how much wood you burn and when you stop feeding it. There is no thermostat. In practice that is less fiddly than it sounds: you learn your tub within two or three uses, and most people end up letting it run slightly hot then topping up with cold.

Internal, integrated or external stove?

Internal	Stove sits inside the tub, submerged. Most efficient — no heat lost to the air — but it occupies bathing space and you are sitting near hot metal, so it needs a guard.
Integrated	Built into the tub wall. Firebox and flue outside, heat exchange against the water inside. One object in the garden, full bathing space, no external pipework to lag.
External	Separate stove beside the tub, connected by flow and return pipes. Keeps all bathing space and puts the fire well away from bathers, but it is two objects and the pipes need draining in a hard frost.

For a UK garden we would generally point you at integrated: it keeps the footprint to one shape and avoids the winter pipe-draining that catches out external-stove owners.

What they actually cost to run

This is where wood-fired tubs win decisively, and it is worth being precise about why.

An electric hot tub is kept at temperature continuously, whether you use it or not. That is what makes it convenient — and it typically costs £40–£80 a month, year-round, before you have got in once. A tub used twice a week still costs the same to keep warm as one used nightly.

A wood-fired tub costs nothing when idle. You pay only for the wood you burn:

Wood per session	Roughly 15–30 kg depending on tub size and outside temperature
Cost per session	£3–£8 at typical UK kiln-dried log prices
Twice a week	Around £25–£65 a month — and nothing in the months you do not use it
Standing cost	Zero. An empty, unlit tub costs nothing

The honest comparison: if you use a hot tub every day, electric may work out similar or better, because you are getting value from the heat you are paying to maintain. If you use it a few times a week — which is what most people actually do — wood-fired is markedly cheaper.

The cost most people forget

A conventional hot tub needs a dedicated electrical supply. For a 32A hardwired spa that means an armoured cable from the consumer unit, a dedicated circuit and Part P notification — commonly £400–£1,200, and more if the tub is at the far end of a long garden.

A wood-fired tub needs none of it. No cable, no trench, no consumer-unit work, no electrician's quote. For a plot with no supply at the bottom of the garden, that difference alone can exceed the price gap between the two types of tub.

Heat-up time — the real trade-off

Here is the number nobody selling these likes to lead with:

800 litres	1.5–2.5 hours
1,150 litres	2–3 hours
1,500 litres	2.5–3.5 hours
1,650 litres	3–4 hours

Those are from cold, with a well-fed fire, in mild weather. In January, add to them.

What that means in practice: a wood-fired tub is something you plan. You light it after lunch for an evening soak, or first thing for the afternoon. It is not a tub you fall into at 10pm on a whim — an electric spa does that and this does not.

An insulated cover makes a real difference here, and to how long the water stays warm afterwards. It is not an optional extra on a wood-fired tub.

Smoke, neighbours and the law

This is the part that catches people out, and we would rather flag it before you buy than after.

A wood-fired hot tub has a flue and produces smoke. That raises two separate issues.

Smoke control areas

Large parts of urban Britain are smoke control areas. The rules are set by the Clean Air Act 1993, as amended by the Environment Act 2021 — and they are commonly misdescribed, so to be precise:

• You must not emit smoke from a chimney of a building.
• You may only burn authorised fuel — unless the appliance is on DEFRA's exempt appliance register.

Government guidance applies this to outbuildings with a chimney, which a hot tub stove effectively is. So in a smoke control area you need either authorised fuel or a DEFRA-exempt appliance. Penalties in England are a civil £175–£300 for emitting smoke, and up to £1,000 for buying unauthorised fuel.

Check your postcode with your local council before ordering — the DEFRA map is indicative only. Our smoke control area guide goes through it properly.

Neighbours, which is a separate question

Even outside a smoke control area, smoke nuisance can be actionable as a statutory nuisance. And well before it becomes a legal matter, it becomes a relationship matter.

Think about where the flue sits relative to your neighbour's windows and washing line, and which way the prevailing wind runs. A tub at the far end of a garden with open space beyond it is a different proposition from one against a shared fence in a terrace.

Water care without a filter

Most wood-fired tubs have no filtration system, which changes how you look after the water.

The straightforward approach is to change the water rather than treat it — empty and refill every week or two depending on use. For a tub used a couple of times a week that is genuinely simpler and cheaper than dosing chemicals, and the water is always fresh.

If you would rather leave the water in longer, chemical treatment works much as it does on any tub. Either way, plan where several hundred litres will drain to.

What base does it need?

Water weighs a tonne per cubic metre, so a 1,500 litre tub is 1.5 tonnes of water alone before you add the tub itself and four people. A filled 1,650 L tub with bathers is comfortably over two tonnes.

That needs a concrete pad, or paving slabs on a properly compacted sub-base. Standard garden decking is not built for it — if you are siting on a deck, get the load rating checked rather than assumed.

Keep the stove and flue clear of fencing, overhanging branches and anything else combustible, and leave the ground falling away so the timber is not standing in water.

Who should buy one

A wood-fired hot tub suits you if:

• You have no electrical supply where you want the tub — this is the big one
• You use it a few times a week rather than daily
• You are happy to plan a soak an hour or two ahead
• You have somewhere for smoke to go, and you are outside a smoke control area or willing to use an exempt appliance
• You actively like the ritual — the fire is part of it for a lot of owners

Buy electric instead if:

• You want hot water on demand with no notice
• You will use it most days
• You want jets, lighting and hydrotherapy — a wood-fired tub is still water, not a spa
• You are in a dense urban setting where smoke would be a problem

Common questions

How long does a wood-fired hot tub take to heat up?

Between 1.5 and 4 hours from cold depending on volume — roughly 1.5–2.5 hours for 800 litres and 3–4 hours for 1,650 litres, with a well-fed fire in mild weather. Cold weather adds to it. An insulated cover shortens the time noticeably and keeps the water warm afterwards.

Are wood-fired hot tubs cheaper to run than electric?

For most people, substantially. An electric tub costs roughly £40–£80 a month to hold at temperature whether used or not. A wood-fired tub costs around £3–£8 of logs per session and nothing at all when idle. You also avoid the £400–£1,200 typically needed to run a dedicated electrical supply to the tub. If you use a tub daily, electric closes the gap.

Do I need planning permission for a wood-fired hot tub?

Planning permission is rarely required for the tub itself. The rules that do apply are about burning: in a smoke control area you may only burn authorised fuel unless the appliance is DEFRA-exempt, and that applies to garden appliances with a chimney. Check with your local council before ordering.

Can you put a wood-fired hot tub on decking?

Only if the deck is rated for the load, and most garden decking is not. A filled 1,500 litre tub with bathers is over two tonnes concentrated in a small area. A concrete pad or paving on a compacted sub-base is the safe answer.

How do you keep the water clean without a filter?

Most owners change the water every week or two rather than treating it — simpler and cheaper than dosing chemicals for a tub used a couple of times a week. Chemical treatment is possible if you want to leave the water in longer.

Do wood-fired hot tubs have jets?

Not as standard, because jets need a pump and therefore electricity. A wood-fired tub is hot water, a fire and a view — if hydrotherapy matters to you, an electric spa is the better choice.