Gas
and oil-fired furnaces provide
warm, even heat throughout
your home by circulating heat
through the ducts.
The heat is created by burning
the fuel (gas or oil) inside
your furnace. (Some furnaces
use outside air to help burn
the fuel; others use air from
inside your home.) When the fuel
burns, the hot gases that are
created go through curved metal
tubing called a heat exchanger
and then out of your home through
a metal or plastic vent pipe.
At the same time, the air that
circulates through your ducts
passes over the outside of the
heat exchanger and takes on the
heat from the hot metal. The
warm air is then circulated through
your home. (By keeping combustion
air and supply air separate,
the heat exchanger allows the
air in your home to be heated
without contaminating it with
the toxic by-products of combustion.)
Boilers create heat the same way but instead of heating air they typically heat your home by circulating steam or heated water through a system of pipes and baseboard or radiator-type heat exchangers.
A furnace or boiler’s efficiency rating, or AFUE (see
Efficiency Ratings), tells you how efficient furnaces or boilers use fuel (gas or oil). Mid-efficiency furnaces or boilers, also known as non-condensing or induced draft units, offer efficiencies from 78% to about 84%. High-efficiency furnaces or boilers also called condensing or sealed combustion furnaces, offer AFUE ratings from 90% to about 96%. Usually, the higher the efficiency, the more expensive the unit.
Some mid and high-efficiency
furnaces offer additional features
that provide greater comfort,
as well as additional energy
savings. For more on these features
see Other
Features to Consider.
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