Buying a Wood Furnace
Wood Furnace Brands
A wood furnace is a device that burns wood or pellets to heat air for use in warm-air or hydronic
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, ServiceMagic
can help you find one.
