Outdoor Wood-fired Boilers
(Hydronic Heaters)

An Outdoor Wood-fired Boiler (OWB) is a heating system located outside the building being serviced. They consist of a large firebox surrounded by a water jacket that can heat water up to 190 degrees F. The whole unit is usually housed in an insulated shed, and includes a smoke stack or chimney. The OWB circulates water through the jacket and into water pipes running underground to deliver hot water to the home for space heating and other domestic uses.

OWBs are designed with an "on/off" cyclical operating pattern. After the fuel in the firebox has been lit, the water begins to heat up. When the water temperature in the water jacket reaches a specified temperature, an air damper closes off air to the firebox – reducing fuel combustion – until the water temperature drops, at which point the air damper opens again to increase combustion in the firebox. In this way, water temperature (and air temperature in the home) is regulated.