typical gas-fired duct furnace is shown in figure
Gas-fired furnaces have three main partsthe
return-air compartment that houses the blower and filter
components, the warm-air compartment that includes
the heat exchanger radiators and combustion enclosure,
and the combustion air and fuel compartment. This
arrangement is shown in figure 4-24.
The components and assemblies of a gas-fired
furnace can be broken down into six units. Each unit is
discussed briefly below. Refer to figures 4-23 and 4-24
as we go along to identify the location of individual
The furnace casing, sometimes called the cabinet,
along with the framework, contains and supports the
components of the unit. It also provides an insulating
chamber for directing return air through the heat
exchanger into the warm-air outlet.
The blower is a centrifugal fan that provides the
circulation required to move warm air across the
heated space. It also pulls the return air from the space
back to the furnace.
The burners are usually the Bunsen type regardless
of their size or shape. Figures 4-25 and 4-26 show
Bunsen burners. The burner nourishes the flame, as it
provides the correct mixture of primary air and fuel gas
to the combustion area.
Figure 4-23.Typical gas-fired duct furnace.