What Products Are Used for Ductwork Installation & Repair?

Published on: May 17, 2013

Ducts are the conduits that transport air from the cooling or heating unit to rooms throughout the house. Proper installation is important because a bad design or leaks could take up to 40% of the air flow away from its intended destination and into nonliving areas such as attics and walls, increasing the HVAC unit’s workload and energy costs. For the same reason, checking ducts for leaks should be part of a regular HVAC maintenance program. Leaks in ducts could also result in reduced indoor air quality as pollutants from the attic are sucked into the system and spread throughout the house.

Ductwork Installation

Ductwork installation requires a number of products to be combined together in order to effectively distribute the airflow throughout the building. The goal is to ensure that the air reaches the points farthest from the central cooling or heating unit and that the distribution is relatively even.

The plenum is the part that takes the air from the HVAC unit and sends it into the ducts.

The ducts are made from a variety of materials. Those closest to the HVAC unit and plenum are the largest because the airflow is greatest there. They are made out of rigid materials such as stainless steel and are sometimes lined with fiberglass or coated with other materials to provide insulation. Flexible ducts are used farther away from the center and are usually made of a bendable metal. The flexible ducts wrap around corners to reach the outer rooms. Care must be taken when installing these ducts because of the risk of puncturing or tearing them and creating air leaks. They too are sometimes covered with insulating material.

The insulation is usually made of glass wool if the duct does not have fiberglass built in. The point of the insulation is to keep the more extreme temperatures from the unairconditioned attics or walls the ducts pass through from changing the temperature of the air flowing through the ducts. For flexible ducts, a protective layer is usually wrapped around the insulation to prevent the ducts from being punctured.

Take-offs are the connectors that send air from the main ducts into the branch ducts.

Fabric ducts are not designed to move air from point to point. Instead, they allow air to intentionally leak over a wider area than a traditional distribution point. For this reason, they should only be used in rooms where air conditioning is desired and not to move air through the attic or between walls.

Registers are known to most people as vents. They are installed in the ceiling or a wall, are the end point for the ducts, and allow the air to enter into the room. A wide variety of sizes, angles, and fin types are available to control the speed at which the air comes out and how it is distributed through the room.

Ductwork Repair

Ductwork repair is a simple process that can usually be a relatively easy do it yourself project if the ducts aren’t buried behind drywall or hard to reach areas of the attic. It consists of a visual inspection to look for large holes or disconnected duct joints, a closer inspection performed by carrying ribbon or some other object along the ducts and looking to see if it is blown by air coming out of unseen leaks, and the sealing of any leaks found. Leaks are commonly sealed by either foil tape or mastic, with foil tape sometimes being used as a base for mastic.

Foil Tape

Aluminum foil tape is specifically designed to be applied to ducts. It is flexible enough to wrap around ducts and the joints connecting them, but rigid enough to ensure a tight fit. Foil tape is inexpensive and as easy to apply as any other kind of tape. Once applied, it will keep the area sealed for years.


Mastic is a gummy substance that produces a similar effect to caulk. It is spread over leaks and joints connecting ducts. It is used either by itself or to cover foil tape for added protection. The seal it creates is effectively permanent. To apply, it is mixed with water and brushed over the desired area. This is done either with a paintbrush or by hand for maximum feel and ease of reaching all the way around the duct. If done by hand, gloves should be worn to protect against cuts from sharp corners or screws.

Duck Tape, Not Duct Tape

Duck tape was first used during World War II to seal ammunition cases and other containers that needed to be kept dry. It was named duck tape because water rolled off it like water rolled off a duck’s back. Following the war, it began to be used to repair air conditioner ducts and became known as duct tape. However, it was discovered that over time the tape dries out, cracks, and no longer provides a strong seal. For this reason, it should not be used to repair ducts.

To avoid ductwork installation and repair problems, contact AC Southeast®. Experienced technicians will be happy to provide tips for do it yourself projects, discuss more extensive repairs, provide an estimate for the installation of new ducts, or schedule duct cleaning and sealing service.