What Size Logs Do You Need for a Wood Fired Hot Tub?
So you’ve got your wood fired hot tub set up, or you’re about to buy one, and now you’re staring at a pile of firewood wondering what actually goes in the stove. It’s a fair question too big and the logs won’t fit or catch properly, too small and you’ll be feeding the fire constantly just to keep the water warm. Getting this right makes the whole heating process smoother and a lot less frustrating.
Let’s go through exactly what size works, what type of wood to use, and a few tricks that make heating faster and more efficient.
The Ideal Log Size
Most stoves used in wood-fired hot tubs UK wide are designed for logs around 25-30cm (10-12 inches) in length, with a diameter of roughly 7-10cm (around 3-4 inches). This size range fits comfortably into the standard firebox without being so thick that it takes forever to catch or so thin that it burns out in minutes.
If your logs are longer than the firebox, you’ll obviously need to trim them down forcing an oversized log in usually blocks proper airflow, and airflow is what keeps your fire burning hot and clean rather than smoldering.
A quick way to check: if you can comfortably close the stove door with the log inside without jamming it, you’re in the right size range.
Why Log Size Actually Matters
It’s tempting to think “wood is wood,” but size genuinely affects three things:
Heating speed
Logs that are too thick take longer to catch, which slows down how quickly your tub reaches a comfortable temperature. Thinner, well-sized logs catch faster and get you soaking sooner.
Airflow inside the stove
Stoves need space around the wood for air to circulate. Overpacking the firebox with oversized logs chokes the fire and causes more smoke than heat.
Fuel efficiency
Correctly sized logs burn more evenly, meaning less wastage and fewer top-ups needed to maintain your ideal temperature.
What Type of Wood Should You Use?
Size isn’t the only factor the type of wood matters just as much.
Best Options: Hardwoods
- Oak – slow burning, consistent heat, ideal for longer soaking sessions
- Ash – burns well even when slightly green, a favourite among UK hot tub owners
- Birch – catches quickly and burns hot, great for getting the water warm faster
Avoid: Softwoods (Mostly)
Pine, spruce, and other softwoods burn fast and can leave more resin residue in the flue over time. They’re fine in small amounts to help get a fire started, but shouldn’t be your main fuel source if you’re using the tub regularly.
Moisture Content Matters More Than People Think
Always use seasoned or kiln-dried wood with moisture content under 20%. Wet or “green” wood doesn’t just burn poorly — it produces more smoke, deposits creosote inside your flue, and genuinely wastes a lot of heat just evaporating the water inside the log before it can burn properly.
If you’re not sure, a cheap moisture meter (a few pounds online) takes the guesswork out completely.
How Many Logs Will You Actually Need?
This depends on your stove size and how cold the water is to start with, but as a general guide:
- Heating from cold (10-15°C water): Around 8-10kg of wood to bring the water up to a comfortable soak temperature over 2-3 hours
- Maintaining temperature once hot: 1-2 logs added roughly every 30-45 minutes
If you’re using the tub regularly, it’s worth keeping a dry, covered log store nearby so you’re never caught out mid-soak with damp wood.
Tips for Efficient Log Burning
- Stack loosely, not tightly – air needs room to move between logs for a strong, clean burn
- Use kindling or firelighters to start – small dry sticks or a firelighter under bigger logs gets things going faster than trying to light large logs directly
- Keep a consistent supply – rather than adding one huge log, smaller regular top-ups maintain a steadier temperature
- Store wood off the ground – damp ground moisture creeps into stacked logs surprisingly fast, even under cover
Buying Pre-Cut Logs vs Cutting Your Own
If you don’t have access to your own woodland or logs, most UK suppliers sell kiln-dried hardwood logs pre-cut to hot tub stove sizes usually labelled specifically for wood fired hot tub for sale stove use, which takes the guesswork out entirely. It’s a bit more expensive than sourcing your own, but the consistency in size and dryness genuinely makes a difference in how easily your fire catches.
Final Thoughts
Getting log size right isn’t complicated once you know the numbers aim for around 25-30cm length and 7-10cm diameter, stick to seasoned hardwood, and keep your wood dry. Do that, and you’ll find your fire catches faster, burns cleaner, and heats your water far more efficiently than randomly grabbing whatever’s in the wood pile.
If you’re still deciding on your setup or want advice tailored to your specific stove size, the team at Tamed Ocean can point you in the right direction.
Frequently Asked Questions
What is the best log size for a wood-fired hot tub stove?
Most stoves work best with logs around 25-30cm long and 7-10cm in diameter small enough to allow good airflow but large enough to burn steadily.
Can I use green (unseasoned) wood in my hot tub stove?
It’s not recommended. Green wood burns poorly, produces more smoke, and can lead to creosote buildup inside the flue over time.
How much wood do I need to heat a hot tub from cold?
On average, around 8-10kg of seasoned hardwood will heat the water over 2-3 hours, depending on starting temperature and outdoor conditions.
Is oak or ash better for a hot tub stove?
Both work well. Oak burns slower and steadier, while ash burns well even when slightly less dry many owners keep a mix of both on hand.
Should I avoid softwood completely?
Not entirely softwood is fine for kindling to start the fire, but it’s not ideal as your main fuel due to faster burn rates and resin residue.
Do UK suppliers sell logs specifically for hot tub stoves?
Yes, many suppliers sell kiln-dried hardwood logs pre-cut to the correct size for hot tub stoves, which saves the hassle of cutting your own.