typical gas-fired duct furnace is shown in figure 4-23.

Gas-fired furnaces have three main parts - the 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.

Basic Components

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 parts.

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.