Best Firewood Types for Heating Your Wood Fired Hot Tub

The crack of a well-seasoned log catching flame, steam rising off the water as the temperature climbs, stars emerging overhead while you wait for that perfect 104°F. This is the wood fired hot tub experience at its best, and it all starts with what you are burning.

The wrong firewood means more smoke, longer waits and constant trips to the woodpile. The right firewood means you are soaking in a couple of hours with nothing but an armful of wood to keep you there all evening. Here is how to choose it, source it and burn it for maximum heat with minimum hassle.

Why your firewood choice matters

The best firewood for a wood fired hot tub is dry, dense, seasoned hardwood with moisture content under twenty percent. Oak, ash, maple and birch all fit: they burn hot, burn long, and bring the water to soaking temperature without filling the air with smoke. The wrong wood means more waiting, more trips to the woodpile, and a haze drifting toward the neighbors.

Hardwoods and softwoods do very different jobs in the firebox. Hardwoods are denser, so they pack more energy into each log and keep burning steadily while you are already soaking. Softwoods catch quickly and burn hot for a short burst, which makes them ideal for getting started but poor for the long haul.

It heats quickly and is very efficient using much less firewood than I had ever thought.

Dave Bishop, Yosemite

Before any of it goes in: never light the fire before the tub is filled. Fill to the line marked on the tub, or at least 4 inches above the chimney collar, and keep the water there the whole time the firebox is hot.

Best hardwoods for heat output

Wood	Burn time	Heat output	Availability	Best for
Oak	Long	Very high	Common	Extended soaks in cold conditions
Ash	Medium to long	High	Common	All-round performance
Birch	Medium	High	Common	Quick heating, pleasant aroma
Maple	Long	High	Seasonal	Consistent overnight burns
Beech	Long	Very high	Less common	Maximum heat in sub-zero weather

Oak

Oak burns extremely hot and keeps going, which makes it a favorite for those sub-zero evening soaks when you want the fire doing the heavy lifting. Both white and red oak work well, though they take longer to season than other hardwoods, often eighteen months to two years.

Ash

The all-rounder. Burns clean, splits easily, and performs reasonably even when slightly less seasoned than other hardwoods. If you can only stock one type, ash is the safe choice.

Birch

Popular across the Nordic countries for hot tub heating, and for good reason. Solid heat with a subtle aroma. One caveat: birch bark contains oils that contribute to creosote if you burn bark-heavy pieces exclusively, so mix it with other hardwoods.

Maple

Steady, reliable heat that suits maintaining temperature through a long evening. It coals well, so the fire keeps producing heat as it burns down. Less tending, more soaking.

Beech

Burns extremely hot with excellent coaling. Harder to source in some regions, but worth stocking for the coldest nights.

When to use softwood

Softwood is not inferior, it is built for a different job. Softwoods ignite quickly and burn hot briefly, which makes them ideal for the fire-starting phase. Once you have a strong flame, transition to hardwood for the sustained heat that actually brings the water up.

Pine

Excellent kindling. Ignites fast, burns hot initially, and smells like a campfire. Use it to get things roaring, then add denser logs on top.

Spruce

Light and quick-burning, common across Canada and often already at the cabin. Good for building initial heat.

Cedar

Splits easily and smells wonderful, which is fitting given what your tub is clad in. Like other softwoods, it works best as a starter rather than a main fuel, and it throws sparks, so keep the chimney cap in place.

Fir

Burns cleaner than pine with less resin, making it a good transitional wood between kindling and hardwood.

How much wood you actually need

• Initial heat-up. From cold to soaking temperature, expect several armfuls of split hardwood. A tub with an internally submerged firebox and good insulation reaches temperature in around two hours on the Small, three on the Standard, and about five on the Large.
• Maintaining heat. Once at temperature, holding it takes surprisingly little. Often just an armful a day, since with the lid on the water loses only two to three degrees Fahrenheit overnight.
• Cold weather. Sub-zero conditions demand more fuel, though 360 degrees of insulation dramatically reduces consumption against a poorly insulated tub.

Firebox design plays a significant role. A submerged firebox, the largest of its kind, transfers heat directly into the water rather than losing it to the surrounding air, which means less wood burned per soak. It also takes regular-length logs, so there is no cutting to a special size.

How dry it needs to be

Seasoned wood has been dried, typically for six months to two years, until its moisture content drops low enough to burn efficiently. This matters more than almost any other factor.

Wet wood hisses, steams and smokes. Dry wood burns clean, which keeps the evening peaceful and the neighbors happy.

• Weight. Seasoned wood is noticeably lighter than freshly cut.
• Cracks. Look for cracks radiating from the center on the cut ends.
• Sound. Knock two pieces together. Dry wood sounds hollow, green wood sounds dull.

Moisture absorbs heat energy that would otherwise warm your water. Wet wood also creates creosote, a tar-like substance that builds up in the chimney and firebox, reducing efficiency and creating a hazard over time.

What to avoid

Burn only clean, dry, untreated wood. Everything below is excluded for good reason.

Treated or painted wood

Never burn treated lumber, painted wood, pallets or construction scraps. They release harmful compounds when burned, dangerous to breathe and to soak beneath. That includes pressure-treated deck boards, old fence posts, and anything with visible paint or stain.

Wood with nails or hardware

Never burn timber containing nails, screws or any other hardware. Check salvaged wood carefully before it goes anywhere near the firebox.

Pellets, accelerants and fire starter logs

None of these belong in a submerged firebox, and using them voids firebox coverage.

Green or wet wood

Beyond the smoke and poor output, green wood accelerates creosote build-up, which reduces airflow and creates a fire hazard.

Resinous softwoods as your main fuel

Pine and spruce are fine for starting fires. Relying on them leads to sticky residue and faster creosote accumulation.

Driftwood

Driftwood carries salt, and burning it puts salt and chloride into the firebox and up the chimney, where it attacks the stove body and flue over time. This is a combustion issue rather than a water one: the tub itself is marine-grade and built to be filled from the ocean. Salt in the water is fine. Salt in the fire is not.

How to heat faster

1. Start with dry kindling and softwood

Build the fire at the rear of the firebox, below the chimney. Start with paper and thin splits, topped with quick-burning softwood. That establishes the flame that will ignite your hardwood.

2. Use split logs rather than rounds

Split wood exposes more surface area, igniting faster and burning more completely. Aim for pieces roughly the width of your fist to start.

3. Keep the air moving while it catches

Keep the firebox lid open about 4 inches while starting, for airflow. Do not pack the firebox tightly or load wood above the internal pipes.

4. Add hardwood once established

With a strong fire going, transition to dense hardwood. That is where the sustained heat comes from.

5. Keep the lid and floating insulation on

Heat escapes through the water surface faster than anywhere else. Using the insulation sheet and cedar lid while heating cuts time to temperature noticeably.

6. Stop adding wood at 95°F

The fire keeps transferring heat as it burns down, so the water climbs to the 101 to 104°F soaking range on its own. Adding wood past that point is the usual cause of an overheated tub. The art of heating a wood fired hot tub covers the whole sequence.

How firebox design affects efficiency

Not all wood fired hot tubs burn wood equally. The firebox design, and the insulation around the tub, determine how much of your firewood's energy actually ends up in the water.

An internally submerged firebox sits directly in the water, transferring heat immediately rather than losing it to the air. External fireboxes heat indirectly and lose significant energy on the way.

Insulation matters just as much. A well-insulated tub retains heat far longer, which means less wood to reach temperature and less to hold it. Firebox capacity plays a role too: a larger firebox takes bigger logs and needs reloading less often.

Clearing ash matters more than most owners expect. A firebox full of ash draws poorly and burns cooler, so the scoop supplied with the tub is a performance tool as much as a cleaning one.

Sourcing and storing

• Where to source. Local suppliers, cutting your own where permitted, or bulk delivery for properties with road access. At the cabin, supplement with deadfall from your own land.
• Stacking and covering. Store off the ground on pallets or rails, covered on top to shed rain and snow but open at the sides for airflow.
• Seasoning timeline. Wood cut this year is ready next year. The best time to stock up is well before you need it.
• Keep it close. A dry supply near the tub matters most in winter, when nobody wants to trek through snow for each reload.

Using what has already fallen on your own property is the lowest-impact fuel there is. More on that in how we source our materials.

One thing to check before the first fire of the season: fire bans. Burning is restricted across much of Canada and the western US through dry months, and a wood fired tub is not exempt. A Hybrid is what keeps a tub usable through a ban, since the electric side carries it while the firebox stays cold.

Built for the fire

The ritual of splitting wood, building a fire and watching the temperature climb is part of what makes a wood fired hot tub different from a humming, glowing spa. It is slower, more intentional, and connected to the outdoors.

That ritual works best when the tub is designed for it. An internally submerged firebox, the largest of its kind, means faster heating and less wood per soak. 360 degrees of insulation keeps the heat where you want it, in the water, even well below zero. And a marine-grade aluminum structure means you can fill from the ocean, the lake, the river or the hose.

Reserve one today.