A wood-fired hot tub harkens back to the days before electricity or access to natural gas. Many hot tub purists love the natural experience of soaking in a tub heated by burning wood. This saves electricity and therefore money, not unimportant.

Using a wood-fired hot tub requires a bit more work than electric or gas hot tub heaters, but the basic principles are the same. Water from the tub reservoir passes through the heating element, then through a filtration system, and finally back into the spa.

The essential difference (from a water heating standpoint) is that a wood fired hot tub heater cannot keep your hot tub's water at a precise temperature like other heating options can. In addition, 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 counteract this, use a paddle or something similar to stir the water occasionally while you're soaking.

The basic operation of a wood-fired hot tub focuses on the heating stove, maintaining the correct water level to cool the stove, and airflow. When lighting a fire in the stove, it is best to use clean burning paper for the initial ignition, followed by dry kindling, covered with criss-crossed logs. The rule of thumb here is simple: the more wood you use, the faster the water in your spa will reach soaking temperature (about 40C). The more wood you add, the longer the water will stay at the right temperature. If the water gets too hot, dampen the fire and reduce the airflow in the stove, both will cool things down pretty quickly.

Smoke is the other potential problem with a wood burning hot tub heater. Using a highly heated, low-smoke fuel source will help reduce the amount of smoke, as will making sure the wood is very dry and not green. Keep the chimney of the stove (if present) clean and free of obstacles. This is very important!