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Applicance
Service Plans
Heating
& Cooling Energy Tips
How BTU's
and EER's work
Maintain
Heating/Cooling Equip
Natural
Gas Safety Tips
Furnace
Efficiency Ratings
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A central furnace or boiler's efficiency is measured by annual
fuel utilization efficiency (AFUE). AFUE is a measure of how efficient
the appliance is in using electricity or fossil fuels (oil or
gas) over the course of a typical year.
An all-electric furnace or boiler has no flue loss through a
chimney. The AFUE rating for an all-electric furnace or boiler
is between 95% and 100%. The lower values are for units installed
outdoors because they have greater jacket heat loss. However,
despite their high efficiency, the higher cost of electricity
in most parts of the country makes all-electric furnaces or boilers
an uneconomic choice. If you are interested in electric heating,
you might consider installing a heat-pump system.
The minimum allowed AFUE rating for a noncondensing fossil-fueled,
warm-air furnace is 78%; the minimum rating for a fossil-fueled
boiler is 80%; and the minimum rating for a gas-fueled steam boiler
is 75%. A condensing furnace or boiler condenses the water vapor
produced in the combustion process and uses the heat from this
condensation. The AFUE rating for a condensing unit can be much
higher (by more than 10 percentage points) than a noncondensing
furnace. Although a condensing unit costs more than a noncondensing
unit, the condensing unit can save you money in fuel costs over
the 15 to 20-year life of the unit.
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