Types of Materials
The primary material for HVAC duct parts is 30-gauge galvanized sheet metal. The parts are already fabricated and can be purchased from HVAC suppliers. Compressed fiberglass panels and rigid foam boards are also used for making plenums and rectangular ducts. Unlike sheet metal, fiberglass and rigid foam boards also have insulating qualities, which eliminates the step of insulating metal ducts.
Central plenums are boxes or air chambers that are connected to blowers that are above, below or adjoining the component. Air pressure builds up in the chambers, which is the central location where treated air is collected and distributed. The air is delivered through ducts that lead to different rooms or spaces.
The two main types of ducts are round (radial) and rectangular. Rectangular and radial ducts are used to construct the main trunk line, which is sometimes referred to as an extended plenum. Round ducts deliver heated or cooled air to the designated locations and are made in widths up to 14 inches in diameter. The available length is as long as 10 feet. Rectangular ducts have a depth of 8 inches and diameters ranging from 10 to 28 inches. Flexible round ducts are available in various widths and length. This type of duct is used for trunk lines as well as supply branches.
A wide variety of HVAC duct parts comprise the accessories necessary to construct a ductwork system, including elbows, take-offs (rectangular ducts), starting collars (round ducts), grilles, stacks, register boots, registers and diffusers. Take-offs and starting collars connect ducts to the plenum. Stacks are short lengths of duct that fit between the studs in walls. Grilles are placed on walls or floors and allow air to be pulled into the furnace. Register boots (boxes) come in a wide choice of sizes and shapes.
Boots are the final components for the duct system, and fit on the ends of the supply ducts to deliver supply air to the rooms through registers or diffusers. The registers are generally rectangular or square-shaped and have horizontal or vertical vanes that can be adjusted to control the volume of air. Support the ducts with polypropylene or perforated metal straps. Steel wire is also used to provide duct support, but it is not the best choice.