Wood is a traditional form of fuel, which was used in the past but is also considered an important fuel in the present, in terms of its suitability for modern gadgets. Wood boilers are heating systems that use wood chips or wood pellets as fuel. There is a difference between the wood boilers that use wood chips and those that employ wood pellets as fuel.

The former is larger since wood chips are larger than wood pellets. The fuel is obtained from forestry thinning and crops from areas located in close proximity to the boilers. Wood is usually dried over a certain period of time, and then subsequently chipped. Wood pellets, which serve as a fuel for wood boilers, is obtained from the compression of sawdust, a readily available industrial waste product. Since a steady supply of sawdust can easily be ensured, the product is highly recommended for small boilers.

Major wood boilers make use of a downdraft wood gasification device. This burns wood of all kinds with varying degrees of moisture present in them. These wood boilers function by extracting the wood gases with the help of an induction fan, and then burning them below the wood to make certain that the combustion is more complete. The wood is repeatedly heated by the burning of gases below it. This ensures the steady rise of gases from the wood.

The wood does not burn, but it makes sure that a steady supply of gas is easily available. As the combustion is limited only to the gases, a wood boiler can burn wood with a greater variety of moisture content. Such wood boilers have a system that entails an automatic switchover to oil heat, gas heat or electric heat backup. Another important trait of such wood boilers is the optional lockout system. This helps in sustaining the secondary fuel mode, in case the wood charge is exhausted.