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Learn about Wood-fired Furnace

Wood-fired Furnace

Wood-fired furnaces are similar to wood stoves, but they heat air that is then circulated through a house through forced air ductwork. However, they don't look like a typical wood stove, instead they look like an oil-furnace. They can be located outdoors or indoors in a basement or mechanical room and require frequent stoking.</p><p>Hybrid combination wood and oil furnaces are also a common heating system type in rural areas. These systems have an oil furnace attached to the wood furnace that is engaged when the wood furnace is not running or providing sufficiently warm air.

Look for an EPA certified wood furnace, 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 furnaces sold in the USA, since 2015. Check that your jurisdiction allows wood furnaces because some cities have restricted their use. Look at the EPA certified list to choose a high-efficiency model. Efficiencies are up to 83%, although the delivered efficiencies are typically 25% lower due to blower operation and duct losses. Find a WETT certified installer (Wood Energy Technology Transfer), for correct and safe installation. Combustion gases must be reliably and safely vented.

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

The furnace 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 house and the insulation levels so that your furnace is not under or over-sized.

Wood furnaces 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.

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