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Buying a Wood Furnace

An outdoor wood furnace is a furnace that burns wood or pellets to heat water (or air) for use in hot water (or warm-air) heating systems. For people with a ready supply of firewood a wood-fired furnace can be a safe and economical way to reduce home energy costs. Most of today's wood furnaces are hydronic wood furnaces, which means they heat warm water to some optimal heating temperature and then pipe it to its desired location.

How Wood Furnaces Work

Outdoor wood furnaces are made up of a cabinet, a sealed firebox, a blower and access doors for stoking the fire and cleaning. Firewood (or other fuels) are burned in the firebox, and that fire heats the water. The hot water is then piped to the building you want to heat though insulated underground pipes.

The next step depends upon the existing mechanism for distributing heat in your home or office. If you have a warm-air furnace and ductwork, heat is removed from the water via a water-to-air heat exchanger and used to heat the air circulating through the ductwork. If you have a forced hot water system, the water can be piped directly into that system. Once the heat has been removed, the cold water is circulated back out the wood furnace and heated again.

Many furnaces have a blower fan that can be used to enlarge the fire, and create more heat. There are also combination wood furnaces that have a gas or oil burner or electric elements as backup. Wood furnaces may also have accessories like electronic air cleaners, humidifiers, and an evaporator coil for central air, or a coil for heating domestic hot water.

Pros And Cons Of Wood Furnaces

The most commonly mentioned advantage of a wood furnace is that they can dramatically cut your enery bills. This is especially true if you need a heating system that heats several buildings, such as your home, a workshop, and perhaps an outdoor sauna. However, there's no magic to this -- you need to have a ready supply of fuel and a willingness to feed that fuel into the furnace on a regular basis.

On the flip side, however, the Northeast States for Coordinated Air Use Management (NESCAUM) released a report in March 2006 that was very critical of the emissions produced by outdoor wood furnaces. In particular they found that average real-world emissions were "twenty times higher than the average in-use emissions of an EPA certified wood stove." The report speculates that these emissions could cause an increase in respiratory and lung problems for people living near outdoor wood furnaces. The US federal government does not have mandatory pollution controls for these furnaces.

In addition to health problems, the NESCAUM report found that manufacturer estimates of wood furnace efficiency were significantly overstated: "Test results... indicate that, in general, most units will have operating efficiencies in the range of 30 to 40 percent."

Installing an Outdoor Wood Boiler

Typically the manufacturer of the furnace will arrange for it to be delivered to your home or business. They will place the furnace somewhere between 20 - 200 feet from other buildings. The installation procedures require that a trench be dug from the furnace to the point at which you will connect the furnace to your existing heating system. Insulated pipes are then buried in the trench to circulate the hot water. There is generally some technical work needed to connect the furnace to your heating system. If you don't know a contractor that can install a wood boiler for you, HomeAdvisor can help you find one.

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