In the first part of my look into the realm of outdoor furnaces the main ingredient was a boiler situated away from the main structure and heated by wood. Insulated pipes run underground from the outdoor furnace to the home and provide warmth either from direct piping in the floors or from a heat transfer unit within a blower unit. This unit can also hook into a pre-existing oil or gas furnace which doubles as a back-up unit in case the wood supply dwindles.

The working model I visited belongs to Freeman who chose the Wood Doctor™ mainly because of its availability in his area. Instead of a sole-purpose option, which is the norm for many users, Freeman has his unit set up to accommodate a variety of heating requirements. It will even heat a swimming pool that will be used for 7 months of the year. In addition, Freeman customized his design in ways that the normal outdoor furnace could handle but was never envisioned.

Figure: C Just inside the house is the main switching area for the heated water. Freeman has also allowed an extra valve for expansion. The smaller zone valves above control heat going in to each room.