The best wood for a wood-fired hot tub is kiln-dried or well-seasoned hardwood — ash, oak, beech, and birch are the top picks for UK conditions. They burn hotter, cleaner, and longer than softwoods, meaning faster heat-up times and far less smoke. Softwoods like pine are fine for kindling, but avoid treated timber, damp logs, and pallets entirely.
There's a big difference between the wood-fired hot tub session you imagined — steam rising, stars out, total silence — and the one where you've been feeding a smoky, spluttering fire for 90 minutes while the water's still lukewarm. The gap between those two experiences? Usually the wood.
Most people spend weeks choosing the right tub, the right spot in the garden, the right cover. Then they grab whatever logs were cheapest on the forecourt and wonder why it's not quite working. It happens more often than you'd think.
This guide covers everything you need to get your fuel choice right: which hardwoods perform best, what to do with softwood, the things you absolutely shouldn't burn, and a quick checklist for buying firewood without being let down. We'll also touch briefly on the wood choices behind the tub itself — because cedar, larch, and thermowood each bring something different to the build.
Quick answer: what's the best wood for a wood-fired hot tub?
Kiln-dried or well-seasoned hardwood. That's it. That's the answer.
Hardwoods are denser than softwoods, which means they store more energy, burn longer, and produce more consistent heat. For a wood-fired hot tub — where you're trying to heat a large volume of water and then hold that temperature — that sustained output matters a lot.
The key benefits of using good hardwood:
- Higher heat output — more energy per log means faster water heating
- Steadier burn — less fiddling, more soaking
- Cleaner combustion — less smoke, less soot build-up inside the stove
- Better temperature control — easier to maintain once you're up to temperature
A medium-sized tub typically needs around 15–25 kg of dry hardwood to reach a comfortable soaking temperature. Use wet or poor-quality wood and you'll need considerably more — and probably a lot more patience too.
The golden rule: dry wood wins
Before you even think about species, think about moisture. Wood with a moisture content above 20% is fighting against itself when it burns. A significant chunk of the energy goes into evaporating the trapped water rather than heating your tub. The result? More smoke, longer heating times, and a frustrating evening.
Seasoned wood means properly dried — typically left stacked in a well-ventilated, covered store for at least 12 months, often longer for denser species like oak. Not "left in the garden for a few weeks." Genuinely dried.
Kiln-dried wood gets there faster through a controlled drying process. The moisture content is reliably brought below 20%, and it performs consistently right out of the bag. It costs more upfront, but many people find they actually use fewer logs overall — which closes the gap.
A few quick ways to tell if wood is properly dry:
- It's noticeably lighter than you'd expect
- The ends show small cracks or checks (the wood has shrunk as it dried)
- Two pieces knocked together make a sharp, hollow sound rather than a dull thud
- A basic moisture meter — inexpensive and widely available — will give you a precise reading
For storage: keep logs elevated off the ground, cover the top to protect from rain, but leave the sides open for airflow. A sunny, breezy spot is ideal. Bring a night's worth inside (or under a sheltered porch) a day before you plan to soak — dry logs that have also warmed up a little light noticeably easier.
Best hardwoods for heating a wood-fired hot tub
All four of these are excellent choices. The right pick often depends on what's available locally and what you're trying to achieve.
Ash
The all-rounder. Lights easily, burns with strong, reliable heat, and produces minimal smoke. It also seasons faster than most other hardwoods, which matters if you're sourcing locally. If you're only going to keep one type of log in stock, ash is probably it.
Oak
The long-game choice. Dense, slow-burning, and excellent at holding temperature once your tub is up to heat. Oak takes longer to get going and needs to be properly seasoned (at least 12 months; fresh oak can take two years). Kiln-dried oak sidesteps the wait entirely and performs brilliantly in winter sessions.
Beech
Clean and consistent. Burns hot with very little ash residue, and holds a steady temperature without dramatic spikes. Well-seasoned beech is a genuinely underrated option.
Birch
Quick and bright. Birch lights easily and heats fast, making it great for shorter sessions or when you want the tub up to temperature without a long lead-in. It burns quicker than oak or ash, so it's worth mixing with a slower-burning wood if you're planning a longer soak.
A practical approach many people swear by: start with birch to establish the fire quickly, then transition to ash or oak to sustain the heat. Simple, effective, and far more satisfying than endlessly stoking.
What about softwoods like pine and spruce?
Softwood isn't bad. It's just different — and it's best used for what it's actually good at.
Pine, spruce, and similar species ignite quickly and produce a lively, bright flame. That makes them ideal for getting a fire going fast, especially in cold weather. Many experienced hot tub owners keep a small amount of dry softwood purely for kindling.
The watch-outs: softwoods burn faster and can produce more resin-based deposits inside your stove over time if they're not thoroughly dry. They also tend to throw more sparks. For a quick start, they're fine. As your main heat source for a long session, hardwood is the better call.
The rule of thumb: softwood to start, hardwood to sustain.
The "please don't" list
A few things that genuinely shouldn't go near your stove:
- Treated or painted timber — the chemicals released when burned are harmful to breathe and can damage stainless steel components
- Pallets — often treated with pesticides or other preservatives; the markings don't always tell the full story
- MDF or plywood — the adhesives and resins create toxic fumes when burned
- Driftwood — looks romantic, but the salt content produces corrosive, unpleasant smoke and accelerates stove wear
- Wet or green wood — not dangerous in the same way, but produces excessive smoke, poor heat, and significant soot build-up inside the heater
Keep it simple: natural, untreated, properly dried timber only.
Log size and stacking: making your stove's life easier
This one gets overlooked, but it's practical and worth five minutes of thought.
Check the firebox dimensions of your specific stove before buying logs in bulk. Many hot tub stoves work best with logs in the 25–30 cm range — shorter than the standard firewood length you'll find at most timber merchants. Split logs also light and burn more efficiently than chunky rounds, so if you have the option, go for split.
For storage at home:
- Elevate logs off soil or grass — ground moisture moves up into wood surprisingly fast
- Cover the top of the stack but leave the sides open; fully wrapping wood in plastic traps moisture rather than releasing it
- Keep a smaller "ready" basket somewhere sheltered — logs that've had a few days under a covered porch or in a shed will light noticeably better than those pulled straight from an outdoor stack in January
A quick aside: best wood for building a hot tub
The wood you burn and the wood your tub is made from are very different conversations — but since both matter to the overall experience, it's worth a brief mention. Build types generally fall into three camps: traditional, lined, and fiberglass.
Cedar wood-fired hot tubs are among the most popular for good reason. Western red cedar has excellent natural rot resistance, strong durability, and excellent dimensional stability, which helps reduce warping and splitting; that matters in a tub because stable staves are less likely to open up and leak. Clear, straight-grain boards are usually preferred for staves, and cedar’s high tannin content adds to its natural water resistance. It's a premium choice that holds up beautifully with basic annual oiling, and with proper care cedar can last 15–20 years. Alaskan yellow cedar is another premium option, valued for its clear, smooth grain.
Larch vs cedar hot tub is a common comparison. Larch is tougher, more readily available in the UK, and more budget-friendly. It works well for frames and cladding but is less naturally rot-resistant than cedar when constantly exposed to water, so it needs more diligent finishing and maintenance.
A fiberglass-lined wooden hot tub pairs a wooden exterior with a fiberglass liner. Other lined builds use a resistant plastic liner inside the wood.
Thermowood wood-fired hot tubs represent the modern alternative — timber that's been heat-treated (without chemicals) to dramatically reduce moisture uptake, improve stability, and increase rot resistance. The thermal modification process improves the wood's insulation properties and eliminates resin seepage, making it well-suited to the heat and moisture of a hot tub environment. According to QTD Group, the process also reduces the risk of mould formation significantly. The trade-off is price, but for a low-maintenance, long-lasting build, it's a strong option.
As a rule of thumb for wood-fired hot tub materials: cedar or thermowood for visible, water-exposed panels; larch works well for structural elements with careful, consistent maintenance.
Buying checklist: choosing firewood without getting caught out
Before you commit to a delivery:
- Is it kiln-dried or genuinely well-seasoned (not just "air-dried for a few weeks")?
- Is the moisture content confirmed below 20%? (Ask, or check on delivery with a meter)
- Is it hardwood, or a hardwood/softwood mix — and do you know which?
- Are the log lengths compatible with your stove's firebox?
- Does the supplier store logs properly (covered, elevated, ventilated)?
- Do you have a plan for storing a delivery at home before it gets used?
A reputable supplier will be happy to answer all of these. If they can't, it's usually a sign the wood hasn't been stored or dried properly.
Frequently asked questions
What is the best wood for a wood-fired hot tub in the UK?
Kiln-dried or well-seasoned hardwood is the best choice for UK conditions. Ash is widely regarded as the most reliable all-rounder — it lights easily, burns with consistent heat, and produces minimal smoke. Oak, beech, and birch are also excellent options. The priority above species is moisture content: aim for wood below 20% moisture for efficient, clean combustion. Fuel choice is separate from tub build, and a well-maintained wooden hot tub can last 15–20 years with proper care.
Is kiln-dried or seasoned wood better for heating a hot tub?
Both work well when done properly. Kiln-dried wood offers more consistent, guaranteed moisture levels and is ready to use immediately. Traditionally seasoned hardwood can perform just as well if stored correctly for 12 months or more. Kiln-dried tends to cost more upfront, but many people find they use fewer logs per session, which offsets the price difference over time.
Can you use softwood in a wood-fired hot tub stove?
Yes, for kindling and getting the fire established. Softwoods like pine and spruce ignite quickly and produce a strong initial flame. They're not ideal as your primary fuel because they burn faster, produce more resin deposits over time, and have lower heat output per log compared to hardwoods. Use softwood to start, then switch to hardwood to sustain the heat.
What wood should you never burn in a wood-fired hot tub?
Avoid treated or painted timber, pallets, MDF, plywood, and driftwood. All of these release harmful fumes when burned and can damage the stove's components. Wet or green (freshly cut) wood should also be avoided — it won't necessarily cause harm, but it produces excessive smoke, poor heat output, and significant soot build-up inside the heater.
How long does it take to heat a wood-fired hot tub?
With good quality, dry hardwood, a medium-sized tub typically takes between two and four hours to reach a comfortable soaking temperature. Heating time depends on tub size, starting water temperature, outdoor conditions, and stove efficiency. Using wet or low-density wood can significantly extend this time and increase fuel consumption.
What's the difference between cedar, larch, and thermowood for a hot tub?
These refer to the material the tub itself is built from, rather than the firewood. Traditional all-wood tubs need more maintenance, including the need to drain and clean them every few days. Hot tubs with a fiberglass or other liner are easier to clean than fully wooden tubs, can be fitted with filtration systems, and tend to maintain water quality for longer. Cedar is the premium choice — naturally rot-resistant, aromatic, and stable in damp climates. Larch is more affordable and durable but requires more rigorous maintenance to hold up when constantly exposed to water. Thermowood is heat-treated timber with dramatically improved moisture resistance and stability, making it a strong low-maintenance option for long-term outdoor use.
The simplest path to a better soak
Dry hardwood for the main burn. Softwood for kindling if needed. Nothing treated, nothing damp.
That's genuinely most of what there is to know. Get the moisture content right, choose ash, oak, beech or birch as your main fuel, and the rest tends to take care of itself. The ritual — stacking the logs, lighting the fire, hearing the crackle as the water warms — is a big part of why people choose a wood-fired tub in the first place. Good wood makes that ritual actually enjoyable.
If you're still searching for the right tub to go with it, take a look at our wood-fired hot tub range — built for proper outdoor recovery sessions, the kind that make the rest of the week feel manageable.