Internal Wood Fired Pool and Hot Tub Heaters

How They Work


Internal Wood Fired Hot Tub Heaters have been used predominately with wood hot tubs to rapidly heat the water. However, the same heater can be used to heat pools, swim spas and other acrylic and concrete style of hot tubs.

An internal hot tub heater sits directly inside the pool or tub and as such 100% of the heat energy in the heater is transferred to the water. Like the external heater, the water around the heater develops a natural convection as the hot water is heated. Hot water is less dense and as such it will rise to the top of the tub and the cold water from the bottom will replace it and it too will then get heated. An internal pool or hot tub heater needs to mount to the side of the tub or fastened to the bottom of the tub as the internal air volume will cause the heater to rise (float).

The firewood is fed from the top of the heater and an air vent above the water line draws the air down into the fire chamber and then out through the chimney. The air flow is controlled by adjusting the air intake using the lid and the damper on the chimney. Because the hot water will layer to the top of the tub or pool, you will need to mix the water every so often to get an even temperature throughout the tub. An external pump can be used, or a simple paddle is often used to mix the water.

Pros and Cons


  • Powerful- will heat the water quicker than the same size external heater as all the heat is directed into the water
  • Easy to install – does not require any piping or ports in the hot tub or pool
  • Convenient- you do not have to leave the tub to add wood


  • No Insulated Cover – heat loss is greater from the tub
  • Less internal Capacity – takes up a lot of internal room in the tub leaving less space for bathers
  • Requires Protective Fence- Because the chimney is very hot a protective fence is necessary to prevent accidental skin contact
  • Specific Water Level – The heater can only be operated when the tub is at the proper water level to avoid any damage or to avoid water from entering the air vent


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Timber Line Water Stoves #835 Kapelus Dr. West St Paul, MB R4A 5A4, Canada

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