Instructions / Assembly

Chapter 28 Ductwork

Flue or vent

Air filter or

electronic air cleaner

Figure 28-3. An upflow furnace has a top-mounted plenum to distribute supply air. Upflow units are typically located in a

basement.

home, Figure 28-4. The air conditioning evaporator

coil is mounted on the bottom of the furnace, inside

the plenum. Supply air travels from the plenum

through ductwork to the living spaces. Return air enters

the top of the furnace. The blower serves for both heating

and air conditioning.

28.2.3 Horizontal Furnace

This horizontal furnace is designed for use in a

crawl space or attic, Figure 28-5. Supply air exits at

one end and return air enters through the other end.

This means the ductwork is located in the crawl space

or in the attic, along with the furnace. These horizontal

furnaces are usually electric, but gas, oil, or heat pump

can be used.

Air Conditioning Evaporators

The A-coil is the most popular type of air condi-

tioning evaporator for residential systems. The slant-

coil and upright-coil types are primarily used for

commercial and industrial systems. Commercial and

many industrial air conditioning systems operate the

same as residential types. The components are simply

bigger (and easier to repair). See Figure 28-6.

28.3 Distribution Systems

There are two types of duct systems commonly used

for supply air distribution. They are the radial system,

which uses strictly round pipe, and the extended plenum

system, which combines round pipes with rectangular

ducts.

28.3.1 Radial Piping System

A radial system is one that uses round pipe

running directly from the plenum to the register hoot

(component that is used to connect the pipe to the

outlet registers). There is a separate run from the

furnace plenum to each register boot. These piping

runs radiate from the furnace plenum, Figure 28-7.

This system is practical where the piping runs are

located in an attic or crawl space. The radial system is

most economical and easiest to install, but is not prac-

tical if the furnace cannot be centrally located. Any