The Ultimate Guide to Wood Fired Hot Tubs
This guide explains how a wood fired hot tub works, how to heat and run one, what a site needs, and what to look for in the build. It is the informational half of the picture. If you are ready to choose a size and heating system, the Wood Fired page carries sizes, options, lead times and the warranty.
What is a wood fired hot tub?
Wood fired hot tubs, also called wood burning hot tubs, are what they sound like: hot tubs heated by wood, with no electricity required. They can be used off-grid where power is unavailable, which makes them a natural fit for cabins, cottages and recreational properties. They also work at home, where owners choose them for the look, the experience, the running costs, or the sustainability a conventional spa cannot match. Some can be dual-fueled with electricity, which makes them workable in residential neighborhoods and guest properties too.
Key takeaways
- Off-grid ready. No electricity required, which makes them viable at cabins and remote properties
- A different experience. Silent and jet-free, built around the ritual of fire and water
- Efficient heating. A submerged firebox brings the tub to temperature in a few hours and holds it overnight on very little wood
- Durability. A marine-grade aluminum structure holds water without depending on the wood swelling, and is more hygienic and more recyclable than all-wood or plastic
- Low maintenance. No jets, no internal plumbing, no complex filtration to service, with no UV or ozone needed
How a wood fired hot tub works
A firebox heats the water directly. It sits either submerged inside the tub, or outside it with a circulation loop. Either way the fire transfers heat to the water and brings it to temperature without electricity. If you already know how to make a fire, you can heat a wood fired hot tub: wood, water and good company are the whole requirement.
A submerged firebox is the more efficient of the two. The stove body sits in the water, so heat moves straight into it by conduction and convection rather than radiating into the air and being carried back by a pump. Warm water rises off the firebox, cooler water sinks toward it, and stirring with a paddle keeps that circulation even so the tub heats as a whole rather than in layers. The part of the stove under water stays at water temperature, and a cedar fence keeps bathers away from the hot upper stove and chimney. On an AlumiTub the firebox is the largest of its kind, so it takes regular-length logs and draws well enough to burn cleanly once established.
What happens after the fire is what separates one wood fired tub from another. Heat leaves through the walls, the base and above all the water surface, and an uninsulated all-wood tub loses it about as fast as the fire adds it. An AlumiTub carries 360 degrees of insulation, a full wrap behind the cedar and a floating layer under the lid, sitting on 3.5 inches of rigid board laid beneath the base during site prep, which is why it holds a soak overnight losing only two to three degrees Fahrenheit and stays at temperature on an armful of wood a day. The marine-grade aluminum structure is what allows that insulation to sit between the water and the cedar without rotting the wood.
Wood fired versus a conventional spa
One distinction before the table, because it trips people up. A conventional acrylic spa and an electrically heated cedar tub are not the same thing. The comparison below is against the acrylic spa most people picture: a molded shell with banks of jets, multiple pumps and yards of internal plumbing. The AlumiTub Electric is the same tub as the wood fired one with a different heat source, so almost none of the right-hand column applies to it.
| Feature | Conventional acrylic spa | Wood fired hot tub |
|---|---|---|
| Power source | Electricity, continuous | Wood, renewable |
| Installation | Professional electrical, and usually a crane | None beyond a flat surface. Rolls into place |
| Maintenance | Higher. Sanitizer, filters and plumbing you cannot reach | Lower. Fill, use, drain |
| Sound | Jets and motors | Crackling wood |
| Servicing | Components sealed inside the cabinet, often in foam | Very little to service |
| Lifespan | Limited by shell and electronics | Generational, with aluminum and steel |
A fuller comparison sits in wood fired hot tubs versus electric spas, and the three AlumiTubs heating systems are compared side by side in the heating options guide.
The drawbacks of a conventional spa
Acrylic spas have their place, but the experience is different. They need professional installation and usually a crane on delivery day, they depend on a treatment routine, and they draw power around the clock whether or not anyone is soaking. Their working parts sit sealed inside a cabinet, so reaching a failed component means a service call, and that is usually what decides whether a spa gets repaired or replaced.
A wood fired tub relies on nothing but fire and water. No hum from jets or filters to compete with birdsong or waves. And it can be filled from whatever water is nearby, whether that is a lake, a river, a well or the ocean.
Is a wood fired hot tub right for you?
To run one, you chop the wood, light the fire, stir the water to distribute the heat, and feed the fire to hold temperature. If that sounds like a chore rather than a ritual, a wood fired tub is not for you, and the Electric or Hybrid is the better answer in the same tub. If underwater speakers and banks of massage jets are what you are after, likewise: the Electric and Hybrid are the same quiet soaking tub with a different heat source and a single circulation jet from the filter, not a spa, and none of the three is built for that experience.
If connecting with the outdoors is the point, it offers something no other tub does. Think of the difference between a coffee pod and a slow pour. Both have their place. One rewards the time it takes.
How to heat a wood fired hot tub
Operating one is simple, though it takes practice to land the temperature where you want it. You will need matches, paper, kindling, larger logs, and a way to fill the tub.
Always fill the tub 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 and risks fire, structural damage or forceful ejection of the chimney assembly. This is the single most important instruction on this page, and it is the one thing that voids firebox coverage.
AlumiTubs can be filled from a hose, pumped from a lake or river, or filled directly from the ocean. Ocean fills are changed every five to seven days rather than left standing, and the tub is rinsed between fills.
Once full, build the fire at the rear of the firebox below the chimney: crumpled paper, then kindling, then small dry logs. The wood needs to be genuinely dry, which is where most first-time disappointment comes from.
Light it and keep the stove lid open about 4 inches for airflow while the fire is establishing. Add larger pieces as it catches, but never load wood above the internal pipes.
Stop adding wood at 95°F and let the water climb the rest of the way to 101 to 104°F on its own. An AlumiTub rarely struggles to get hot. The more common problem is overshooting. If it does run hot, add cold water away from the stove and stir with a paddle.
Once at temperature, an armful of wood a day holds it. With the insulation and lid in place, a wood fired tub loses only two to three degrees overnight, which is why the second evening in a row takes a small maintenance burn rather than a full heat-up. Never drain below the fill line until the firebox has fully cooled.
Sunday morning 8am. Hadn't added a log for 11 hours and it was still 103.
Marc Young, Bowyer Island BC
How long does it take to heat?
Between 2 and 5 hours depending on size and conditions: around two hours for the Small, three for the Standard, and about five for the Large. Reheating an already-warm tub is much faster than starting from cold.
What affects it:
- Water and air temperature. A January fill from a cold well behaves differently from a summer hose
- Firewood. Dry, seasoned wood burns hotter and cleaner
- Stove design. Submerged fireboxes outperform external ones
- Insulation. Lids and side insulation stop heat leaving as fast as you add it
- Water volume. 315 US gallons on the Small, 420 on the Standard, 650 on the Large
- Circulation. Stirring distributes heat evenly rather than letting it stratify
An Electric works the other way round. It takes up to fourteen hours from a cold fill, at roughly three degrees an hour, so it is designed to hold a temperature or run on a schedule rather than be heated on demand. On a Hybrid you get both, and running the fire alongside the element is faster than either alone.
Traditional cedar tubs have no insulation layer, so heat loss is higher throughout. Use the lid whenever the tub is not in use, and place the floating insulation on the water surface beneath it. How long it takes to heat goes through each variable and how to run the fire well.
I can't believe the tub stays so hot. It heats so easily and the next morning when we went to use it, it had only dropped 3 degrees. It's well insulated and well made.
Jess Krutz
Winter use and winterizing
Letting a tub freeze will damage it, and can create a hazard the next time it is used.
Winterizing an AlumiTub can be as simple as draining and wiping it out before you leave, once the firebox has cooled. If water is scarce, or the lake you draw from is frozen, you can leave it filled provided you have power for a stock tank heater or pond de-icer. Check its rated volume against your tub size.
If the tub is attended and you want to use it through winter, heating it periodically is enough to hold the water above freezing. AlumiTubs have been tested heating on wood in ambient conditions as cold as minus forty-four degrees Celsius.
On an Electric or Hybrid there is a third option: freeze protection circulates the water automatically from around 44°F, for as long as there is power, so an unattended property does not need draining every time you leave. Plan for a long outage separately, and on a Hybrid the firebox covers exactly that gap.
Siting and setting up
Choosing a location
Most wood fired hot tubs sit on any level surface: ground, deck, patio or concrete pad. What matters is the filled weight.
| Size | Diameter | Water | Empty | Filled |
|---|---|---|---|---|
| Small | 60" (5 ft) | 315 US gal | 200 lbs | 3,200 lbs |
| Standard | 72" (6 ft) | 420 US gal | 220 lbs | 5,000 lbs |
| Large | 84" (7 ft) | 650 US gal | 300 lbs | 7,000 lbs |
Depths of 44 and 48 inches add roughly 1,000 lbs to the filled weight. Seating by size and depth is on the Wood Fired page, and what size you actually need works through the choice.
If the tub is going on a structure, confirm it carries the filled weight at full capacity. That figure is what decides whether a deck needs work, and finding it late is how a project stalls.
Keep the chimney at least ten feet clear of any overhanging structure. Sparks do fly, particularly in dry season, and it is worth confirming exact requirements with your local fire authority. Leave enough room around the tub to load the firebox without brushing against it when hot, and think about where firewood and lids will live.
Rigid insulation beneath the tub is required on concrete, pressure treated wood and gravel, as a protective barrier against dissimilar metals and to avoid denting the base. Two layers, 1.5 inch and 2 inch, giving about 3.5 inches total, is the recommended base for any setup: it improves heat retention and cuts heat-up time. That sits alongside the 360 degrees of insulation around the tub and the floating layer on the water surface.
All three sizes are 38 inches deep, which is also the dimension to know for rolling through a gate or fitting a trailer.
Draining
Plan this before the tub arrives, particularly if you intend to run without filtration, since the tub will be emptied regularly.
The optional Drain Kit takes a garden hose and stubs out from the side, so water empties wherever suits: a garden bed, or back to the lake or ocean it came from. Alternatives include a submersible pump or a siphon.
Without the Drain Kit, a 1.25 inch snap drain plug seals from the inside. With it, use a 1 inch hose and a mechanical clamp, and leave the external valve open through freezing conditions.
Setting up
Cedar tubs supplied as kits can be difficult to assemble without carpentry experience. An AlumiTub arrives pre-assembled, and on a prepared site setup takes about an hour whichever system you have.
- Set the tub on the prepared insulated base, with the Drain Kit aligned in its channel
- Wrap the insulation around the outside and tape the seam
- Position the cedar boards beneath a ratchet strap, working from the front toward the firebox side
- Secure with the stainless bands: top 4 inches from the rim, bottom 4 inches from the base, middle at 19 inches. Tighten evenly and do not overtighten, which can damage rivets
- Fit the chimney into the stove collar, place the lid on the firebox, and hang the thermometer on the cedar fence
- Fill with water, then light the fire
Extra cedar boards are supplied for seasonal shrinkage. Keep them, because gaps will need filling as the wood moves. How to prepare for arrival covers the site in detail, and owners have moved theirs by ATV, boat and kayak; the gallery has the evidence. The FAQ page carries the full video library, including wood fired heating and setup.
At home, off-grid, and for guests
Residential use
Check municipal bylaws before buying, since some areas restrict wood smoke. Because the firebox is submerged, these are generally not treated as an open flame, and they operate much like a household wood stove. When in doubt, ask your local fire department rather than risk not being able to use it.
Dual fuel
If wood use is restricted, or you simply want the option, the Hybrid carries both systems in the same tub, run either alone or together. The common patterns are heating with wood and holding temperature on electric afterward, running both at once to cut the heat time, and heating entirely with wood while the electric side keeps filtration and freeze protection going. Filtration can also be added to a Wood Fired on a standard 120V outlet to extend water life, and that same equipment converts to 240V heating later.
Guest properties and short-term lets
Wood fired tubs are in demand with hosts, and for good reason. Without filtration, the tub is emptied and refilled between bookings. With high turnover, filtration and electric heating make far more sense: the water is hot and clean on arrival without briefing anyone on lighting a fire, and a 50 micron filter holds a single fill for three to four months.
No UV or ozone needed. Most spas fit them to reduce sanitizer demand, because jets and internal plumbing give water places to sit. An AlumiTub has neither. Keep the water in range and demand stays low on its own. Does your hot tub need UV or ozone? covers it in full.
We hear from hosts every year whose guests lit the fire before filling the tub. That warps the firebox and takes the tub out of service. Make sure guests know to fill to the line first, keep the manual on hand, and show them how to get the fire going.
What to look for in a wood fired hot tub
A metal structure, and which metal
AlumiTubs pioneered the aluminum wood fired hot tub in 2001 to solve the problems inherent in all-wood construction, and others have followed since.
A metal structure gives durability, hygiene and winter performance, and it can be left empty without consequence because it does not depend on the wood swelling to seal. Stainless steel is often assumed to be the better metal for the job; it is a different one rather than a superior one. Both protect themselves with a self-repairing oxide film, and in a tub kept within its water care ranges neither corrodes or pits. Aircraft, boat hulls and Airstreams are riveted aluminum rather than stainless, for the reasons that apply here: a third the weight, far better heat transfer, a riveted construction that keeps the full strength of the alloy at every joint, and a metal built to take sea water, which ordinary stainless does not. What stainless tolerates is chlorine, and that matters only where chlorine is required in a commercial setting. For a tub people move themselves, fill from whatever water is nearby and leave empty for a winter, marine-grade aluminum's properties fit, which is why we build with it. Aluminum vs stainless steel hot tubs goes through it question by question, and every hot tub material compared sets the metals against acrylic, cedar and plastic.
Fiberglass and plastic are lower maintenance than all-wood, but less hygienic than metal, heavier, and not recyclable at end of life. They also cannot be customized with drain ports, filtration or alternative heat sources.
An internal, submerged firebox
Submerged fireboxes are more efficient and safer. They heat the water directly, and the submerged portion stays cool to the touch, with a cedar fence preventing contact with the hot upper stove and chimney. Paired with insulation and a lid, that is where the heat retention comes from.
Craftsmanship and materials
Locally sourced materials, built in our own shop, inspected and pressure-tested with water before shipping. The cedar comes from a neighbor, Robert, who lives down the road in Gibsons, British Columbia. He mills only trees that have already fallen or that pose a fire hazard, and every board is milled on site. More in how we source our materials.
Room to change later
Drain placement, ports for filtration, and compatibility with other heat sources all matter more in ten years than they do today. A Wood Fired can be built with the optional compatibility ports that allow heating or filtration to be added later without rebuilding the tub, which is what makes going Hybrid an upgrade rather than a replacement.
Serviceability
Worth asking of any tub you are considering: when something eventually needs replacing, can anyone reach it? On an Electric or Hybrid AlumiTub the whole heating and filtration system sits inside the cedar step against the tub, concealed but reachable, with every part replaceable and nothing to dismantle. A wood fired tub has less to service in the first place. Either way, a structure built to last decades is only worth much if the parts attached to it can be reached.
We have happily been using our AlumiTub for nearly 20 years. Thank you for building such a remarkable product. I can't tell you about the countless happy hours we have spent in its warm confines.
Heidi and Bruce Reugg
Common questions
What is a wood fired hot tub?
A hot tub heated by wood rather than electricity, using a firebox that is either submerged inside the tub or mounted externally. No power is required, which makes them workable off-grid at cabins and remote properties. Some can also be dual-fueled with electricity for year-round use where fire bans apply.
How much water does a wood fired hot tub need 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 and risks fire, structural damage or forceful ejection of the chimney assembly.
How long does a wood fired hot tub take to heat?
Between 2 and 5 hours depending on size and conditions: around two hours for the Small at 315 US gallons, three for the Standard at 420 US gallons and five for the Large at 650 US gallons. An Electric works the other way round, taking up to fourteen hours from a cold fill, so it is held at temperature or scheduled rather than heated on demand.
Is an electric cedar hot tub the same as an acrylic spa?
No. An acrylic spa is a molded shell with banks of jets, multiple pumps and extensive internal plumbing, usually needing a crane to install. An electric cedar AlumiTub is the same tub as the wood fired model with a different heat source: marine-grade aluminum, cedar, a single 30 gpm jet and no plumbing loops, rolled into place without a crane.
How long does it take to set up a hot tub?
About an hour on a prepared site, whichever heating system you have, because the tub arrives pre-assembled rather than as a kit. On an Electric or Hybrid, the electrical connection is made at the same time by your electrician.
What surface can a wood fired hot tub sit on?
Any flat, level, fully supported surface that carries the filled weight: 3,200 lbs for the Small, 5,000 for the Standard and 7,000 for the Large. Rigid insulation beneath the tub is required on concrete, pressure treated wood and gravel, both as a barrier against dissimilar metals and to avoid denting the base.
Ready to choose one? Sizes, depths, heating options, lead times and the 25 year structural warranty are on the Wood Fired page.
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