Wood Fired Hot Tubs and Wood Burning Stoves

Wood Fired Hot Tubs & Wood Burning Hot Tub
wood fired hot tub

Wood Fired Hot Tubs & Wood Burning Hot Tub

Northern Lights is a leader in manufacturing wood fired hot tub using the same 100% clear western red cedar we use in all our hot tubs. Wood burning hot tubs are popular amongst purists that claim the combination of a wood hot tub and a wood stove represents the ultimate in hot tub soaking experience.

Most wood fired hot tubs are used in rural locations that have access to plenty of wood. This certain reduces the operational costs of using a hot tub. The wood burning hot tub uses no electricity and thus there is no forced circulation system found on our other jetted hot tubs. Instead the natural principal of thermosiphon is used.

Thermosiphon is the physics that hot water rises. By using our Timberline wood fired hot tub heaters, the fire heats the water which slowly rises to the top port of the hot tub. At the same time cold water is drawn into the heater to be heated. This provides a natural convection that needs no pump.

how a wood fired hot tub works

Wood fired hot tubs come in two designs

Wood hot tub heating designs

internal wood fired hot tub heater

Internal Heater

external wood fired hot tub heater

External Heater

Northern Lights Cedar Tubs uses the external heater design for our hot tubs as there are a few significant advantages that we feel make them a superior choice

Advantages of External wood fired hot tub heater

  1. Because the heater is outside the tub the tub can seat more people. A internal heater consumes nearly 1/3 of the internal space requiring a much larger hot tub to fit the same number of persons as an external heater

  2. Use of a full insulated cover is possible. A hot tub loses nearly of its heat from the top as hot water rises. With an internal submersible heater it is impossible to use a fully insulated cover to retain the heat. With a full insulated cover you can leave the tub in the evening and in the morning the water temperature will still be warm enough to have a hot tub without restarting the fire.

  3. No critical water level! With a submersible hot tub heater the water level must be maintained within inches to protect the water heater from being exposed and melting. The problem arises when bather overflow the hot tub (happens often during parties). Now before the last person(s) leaves the hot tub, more water is required to be added in order that the water level is brought back to the operational level. This usually means getting out the hose and adding cold water while bathers remain in the hot tub until this process is finished

  4. Chimney is not over the hot tub. An external hot tub heater has the chimney away from the wood fired spa so there is no chance of contact with a hot chimney. With an internal wood hot tub heater, the chimney is within inches of the bathers and there is more chance that smoke and sparks fall directly back to the bathers in the wood fired hot tub.

  5. Cleaning most internal heaters have a fencing system and a heater mounted to the floor. This makes cleaning the wood fired hot tub very difficult in the heater region. In some cases you need to fully disassemble protective fence to access the floor area that can often trap leaves, grass, and sand.

  6. Fueling hot tub from outside means less debris ends up in the hot tub! Loading wood directly over the hot tub water inevitably causes wood and ashes to land in the water requiring frequent cleaning. By controlling the fire away from the hot tub, there is no debris that ends up inside the wood burning hot tub.

Maintaining a wood fired hot tub

A wood fired hot tub is normally used differently than a regular electric or gas fired hot tub. With a wood burning hot tub, the users typically fill the hot tub and use it a couple times then drain the water. With this type of short term use there is no need for chemicals which is a great advantage to those that want a pure chemical free hot tub experience.

Like any wooden hot tub the exterior should be stained if the customer wishes to keep the rich cedar color. If left unstained the hot tub will eventually turn to a natural grey color.

filter system for wood burning hot tub

Optional Filter and Jet Option

Our wood burning hot tubs also have the option of adding a pump filtering system with 4 jets. The optional upgrade is available in a 110-120 VAC power source that can plug into a home outlet that has a GFIC protected plug. With this option customers get the added use of hydrotherapy massage jets. The other reason customers often add this option is that it will filter the water. This means they can maintain the water clarity without having to frequently drain the tub. By adding a filter system a customer can reuse the water for months without having to drain it. If you are planning to use a wood fired hot tub in a vacation home or on weekends, you can expedite the hot tub experience with this option as you don't have to fill the hot tub on every visit!

Temperature Control & Heating Time

The essential difference (from a water-heating standpoint) is that a wood fired hot tub heater cannot keep your hot tub's water at an exact temperature, as the other heating options can. Moreover, the heat will tend to stratify, meaning the hotter water will rise to the top, while the cooler water will sink to the bottom. To combat this, use a paddle or similar implement to stir the water occasionally while you soak. The optional Filer option will help reduce the stratification by force mixing the water.

Controlling the temperature and heating times will depend on the type of wood, the water temperature, and external outdoor temperature. However by using the same type of wood a user will quickly get the feel for the right amount of wood quantity and the heating time required to reach the optimal water temperature. It is important to mix the water to get an accurate water temperature before you enjoy your hot tub as the top may be hot but the bottom is only luke warm.

The heat up time of a wood fired hot tub will depend on the water volume and the size of wood fired hot tub stove that is used. This chart below is an approximation based on a Timberline Wood Water Stove. For most hot tubs a Medium "Blaze" size stove is recommended (55,000 BTU) for our smaller Ofuro Japanese Hot Tubs a smaller "Camp Fire" Model (30,000 BTU) is recommended,

Heating Rate* of Various Size Wood Heaters

Water Volume

Water Mass

Temperature Rise F/hour

US Gal



Camp Fire (35 MBH)


Blaze(55 MBH)


Inferno (105 MBH)









































































*Excludes heat loss of tub/pool


Controlling the Hot Tub Fire

When starting a fire in the stove, it's best to use clean-burning paper for the initial ignition, followed by dry kindling, overlaid with criss-crossed logs. Initially the air flow should be open to MAX in order to get the most air into the fire. The rule of thumb here is simple: the more wood you use, the faster the water in your hot tub will get to soaking temperatures (about 104 F). The more wood you add, the longer the water will remain at the proper temperature. If the water gets too hot, damper the fire using the chimney damper and reduce the airflow into the stove, both of which will cool things down pretty quickly

Northern Lights Wood Fired Hot Tub

Timber Line Wood Hot Tub Heater