Exterior wood furnaces hit the market some years ago, and their popularity continues to rise. A stand-alone unit consists of a small building outside the house that contains a large wood-burning stove. The stove heats a jacket filled with water, which is then pumped into the house through a set of underground pipes. The pipes enter the house and travel to a conventional air handler inside a furnace.
Inside the furnace the water passes through a heat exchanger unit that acts and looks much like the radiator on the front of a car. Water flowing through the heat ex-changer gives up its heat to the air, pushed by the blower fan in the furnace. The heat is then distributed throughout the house through the existing ductwork.
The advantages to such systems are many. They require fueling only once or twice a day and burn large logs that don't require much splitting or cutting. The combustion process takes place safely outside the home. And the mess of hauling, splitting, and storing wood is all confined to the outdoors. The only thing that enters the house from the system is the hot water traveling through the piping. Provided with a source of wood for the winter, a homeowner could heat his or her entire home with such a system instead of just a room or two, as is typical with a woodstove or insert. If retrofitted to an existing HVAC system, the original gas or oil burner can be left in place, providing a convenient backup if, for instance, the occupants are away for several days.
Corn and Pellet Stoves
In areas where field corn, usually used to feed livestock, is available inexpensively, corn stoves are another heating alternative. Corn stoves have a hopper on top or on the side into which bags or bushels of loose corn are deposited. A thermostatically controlled auger shuffles kernels of the corn into a small firebox a few at a time. Inside the firebox a clean, intense fire combusts the corn, turning it into heat that is moved around the room by a small fan.
Homeowners with access to a small field and the means to plant and harvest their own corn or access to inexpensive corn purchased directly from a farmer or grain elevator can generate their own heat economically with a corn stove. Venting the stove can be accomplished via a small fluepipe that can either penetrate the roof or exit through a sidewall of the house. The latter feature can make the installation of a corn stove easier than a woodstove, in some cases.
Bags of corn can be stored in a compact space, can be hauled easily, and don't require any further processing -- unlike the cutting and splitting necessary with wood. Because corn contains oil and ethanol, both of which burn cleanly, only a small amount of ash develops in the firebox. Some corn stoves draw combustion air from outside the house, eliminating the need for make-up air that otherwise would be drawn inside through holes and gaps in the building's exterior shell.
Corn stoves require electricity to operate and thus cannot run during a power outage. However, some have provisions for a backup battery that allows the stove to function in emergencies.
Some corn stoves can also burn pellets -- compressed nuggets of sawmill waste. There are also pellet stoves available, designed only for that use. Corn cannot be burned in pellet stoves. Pellets are available in bags from farm and feed stores, as well as from places that sell wood and pellet stoves. Pellet and corn stoves are also available in fireplace insert configurations.