How It Works
A gas-fired furnace produces hot air to heat a home through
an air duct system. Gas-fired boilers - also called gas furnaces - produce hot
water or steam for a baseboard or radiator heating system and for general hot
water use. Both systems use either a natural gas line or a propane tank. They use
a combustion system consisting of a blower, fuel supply, ignition system (or
pilot light) and a control system.
What Can Go Wrong?
A furnace has many components that can fail, most of which
can be repaired by maintaining or replacing individual pieces. For example, the
burner or blower motor can fail and need replacement, or components in the
control system can fail. Replacement is usually required when a combustion
chamber fails in a hot air furnace or when water leaks in a boiler system.
Heating is the largest energy expense in most homes,
accounting for 35 to 50 percent of annual energy bills in colder parts of the
country. Gas-fired home furnaces range in size from 13.2 kilowatts (kW) to 88
kW. The average home using gas consumes 49,000 cubic feet of gas per year for
space heating, producing approximately 5,733 pounds of carbon dioxide (CO2).
Gas-fired furnaces and boilers are major energy consumers
and sources of CO2 in the home. Gas furnaces are ranked according to
their annual fuel utilization efficiency (AFUE) which is a representation of
the energy efficiency of the furnace during the heating season. It can range
from 65 percent in older units to 97 percent in newer ones. When replacing the
furnace, the higher the AFUE, the lower the energy usage, energy cost and CO2