Wood-fired Boiler

Wood-fired boilers are similar to wood stoves, but they heat water or glycol that is then circulated through a house through a radiant heating system such as hydronic in-floor heat, cast-iron heaters, hydronic walls or hot water baseboard heaters. However, they don't look like a typical wood stove, instead they are typically much larger.

They can be located indoors in a basement or mechanical room or outdoors and require frequent stoking.

They can also be combined with a typical oil, gas or electric boiler that is engaged when the wood boiler is not running or providing sufficiently hot water.

Look for an EPA certified wood boiler, which puts limits on the amount of particulate and other air pollution the stove is rated to emit. EPA certification is now a requirement for new wood boilers sold in the USA, since 2015. Look at the EPA certified list to choose a high-efficiency model - efficiencies are up to 87% (although the delivered efficiencies are typically lower due to pump operation and piping heat losses). Find a WETT certified installer (Wood Energy Technology Transfer) for correct and safe installation. If located indoors, combustion gases must be reliably and safely vented.

Check that your jurisdiction allows wood boilers because some cities have restricted their use. Outdoor models are best suited to rural properties where they can be sufficiently set back from neighboring properties.

The quality of your firewood also matters. Hardwood logs that have been cut and allowed to dry for at least a year before use are the best, increasing burn efficiency and reducing creosote, soot, and harmful air emissions. The recommended water content of the wood when burned is 15-22%.

The boiler must be appropriately sized to meet the heating requirements of your home. Be sure to have a heating contractor perform heat load calculations based on the size of the home and the insulation levels so that your boiler is not under or over-sized.

Wood boilers use a renewable energy source, if the wood is harvested sustainably. However, the smoke from the chimney still contains significant air pollutants that are hazardous to health, especially in urban areas where they can become concentrated and mixed with other urban air pollution.

Use of fire has a very long history. Researchers recently discovered evidence of controlled use of fire by Homo Erectus, an ancestor of the human species, one million years ago. The 2012 discovery, in the Wonderwerk Cave in South Africa, pushed the origins of the use of fire 300,000 years earlier than previously thought.