How Wood Burning Hot Tubs Work

Wood fired hot tubs are an incredible way to experience the outdoors in all its glory. Like gathering around a campfire, it invites us to pause, take notice of the natural environment, and come together for quality, connected time. It offers a soak that is truly elemental, and it presents a ritual of heating the water by fire alone that gives purpose to being outside and reason to dwell there longer. If you already know how to make a fire, you can heat a wood fired hot tub. All you need is wood, water, and good company.

Wood fired hot tubs can bring you closer to nature than any other hot tub can. They are made to bring you to the water's edge, take you high in the mountain tops, or deep in the woods, and they can go places no electric hot tub can. They work by heating the water directly with a firebox, either submerged inside the tub or located externally. With both types, the fire transfers heat to the water, bringing it to temperature without the use of electricity.

1. Fill the tub with salt or fresh water

You can fill a wood fired hot tub from a lake, ocean or river near your property, or set up right on the shore. Always fill before lighting the fire. Fill to the line marked on the tub, or at least 4 inches above the chimney collar, and keep the water there the entire time the firebox is hot. Firing an empty or part-filled tub warps the firebox, creates a serious safety risk, and voids firebox coverage.

Once it is full, build a fire with wood and kindling, light the stove, and listen to the fire crackle, the frogs croak, and the trees rustle in the wind as it heats. Chopping the wood, lighting the fire and letting it heat the water is an elemental way to enjoy the outdoors.

Marine-grade aluminum is what makes the range of water sources possible. More in saltwater against freshwater, and on sourcing water at a remote property in how to handle water access. Ocean fills are changed every five to seven days rather than left standing, and the tub is rinsed between fills.

2. Light a fire in the stove

Building a fire is a simple art. Gather dry wood, kindling and paper. Place tinder at the bottom, stack kindling in a teepee or grid shape over it, and ignite the tinder. Keep the firebox lid open about 4 inches while starting, for airflow. Build it up by adding heavier pieces of wood, and never load wood above the internal pipes.

The firebox is the largest of its kind, so it takes regular-size logs rather than asking you to split wood down to fit.

Heat-up takes 1.5 to 5 hours depending on size and conditions: around two hours for the Small, three for the Standard and about five for the Large. Dry, seasoned wood makes a considerable difference, which is covered in the best firewood to use and in more depth in how long it takes to heat.

3. Stir the water

Create circulation using a paddle or a long piece of wood, bringing the warmer water that rises to the surface down through the tub so heat distributes evenly rather than stratifying.

4. Stop adding wood at 95°F

Once the water reaches 95°F, stop adding wood and let it climb the rest of the way on its own. The fire keeps transferring heat as it burns down, and the water settles into the 101 to 104°F soaking range without overshooting. 104°F is the maximum.

Adding wood past that point is the usual cause of an overheated tub. If it does run hot, add cold water away from the stove and stir, or wait for it to cool before getting in.

5. Maintain temperature with an armful of wood a day

AlumiTubs are built with 360 degrees of insulation, so the tub not only gets hot but stays hot, holding temperature on roughly an armful of wood a day. A submerged firebox transfers heat straight into the water rather than radiating it outward, which gives better efficiency, a hotter burn and far less smoke once established.

Put the cover on overnight and the water stays within two to three degrees. Put a log on in the morning while you drink your coffee and it will be back to soaking temperature before you have finished breakfast. The marine-grade aluminum structure is what allows that insulation layer to sit between the water and the cedar.

Never drain below the fill line until the firebox has fully cooled.

To shorten the initial heat time, or to keep soaking during a fire ban or in a residential area where wood fire may not be permitted by municipal bylaws, the Hybrid and Electric make hot tubbing workable year-round, in every climate and at any property. More on the trade-offs in the complete guide to heating options and the benefits of a wood fired hot tub.

To see one in action, the FAQ page carries the full video library, including wood fired heating and setup.