If you live in a suburban or rural area near a source of cheap wood, you could heat your home for the entire season for the cost of one month�s electric heat bill. An outdoor furnace requires less tending, eliminates respiratory problems caused by burning wood indoors, and keeps the wood burning mess outside.
There are a surprising number of outdoor furnace manufacturers with a wide range of styles and designs to accommodate different heating capacities and fuel sources. Some of these furnaces have the capacity (500k Btu) for commercial applications.
Burns Best makes a corn or wood pellet version. Taylor Waterstoves has a multi-fuel model that burns coal or wood. Hardy Manufacturing makes an all stainless steel furnace with a built in hot water exchanger.
One of the selling points of an outdoor furnace is the convenience of locating it near the wood fuel source. Since the water heated by the furnace is pumped to your home through insulated, underground piping, the furnace can be set up as close as 2 feet, or as much as 500 feet from your house.
All outdoor furnaces are designed to work with any existing heating system and can be thermostatically controlled. If you have a forced air system, you can use the existing duct work but you will need to install a water-to-air heat exchanger in your furnace. Your furnace is still available as a back up.
If you already have radiant floor heating, you would connect the underground feed from the outdoor furnace to the existing circulating pump.
For radiant baseboard heat, you can connect the piping directly to an existing boiler or install a water-to-water heat exchanger. By adding the water-to-water exchanger, you receive the added benefit of free hot water while the existing furnace functions as back up.
An outdoor boiler can even be used to heat your swimming pool, driveway, work shop, greenhouse, or multiple buildings.
The firebox designs vary from manufacturer to manufacturer, but all are constructed from stainless or carbon steel. Although each manufacturer claims to be using a grade of stainless steel superior to the competition, they all agree that heat transfer efficiency is almost 3 times better with 16 gauge stainless steel than with 3/8" carbon steel. An all stainless steel firebox also resists rusting and burnout that occur in standard carbon steel.
Some fire boxes are large enough to accommodate a 30� diameter by 72� log. The problem I would have is getting a log that size into the firebox. Normally, outdoor furnaces are loaded twice a day. Burn times per load vary from 12 to 96 hours depending on what you�re heating, the outside temperature and how well your house is insulated.
One trait all outdoor furnaces have in common is versatility. What ever your heating needs are or the type of fuel you burn, it�s possible to design a system for any heating scheme you can imagine.