How to Repair HVAC Ductwork Leaks

How to Repair HVAC Ductwork Leaks
December 23, 2015 nobleair

Residential HVAC ductwork leaks are quite undesirable to homeowners because these are a sure source of energy waste. Unfortunately, these can go undetected for extended periods of time. Air conditioning ductwork leaks are most commonly found along joints where lines branch-off from one another. These can be caused by aging and normal wear and tear, or, damage done by insect and animal pests. Regardless of the cause, when home ductwork leaks, it causes cooled or heated air to be lost into the void around it, making the central heating and air system work harder and run longer to achieve the desired temperature. Therefore, it’s important to know how to repair HVAC ductwork leaks.

How to Repair HVAC Ductwork Leaks

The first step in fixing residential ductwork is to locate leaks. Unlike some air conditioning and heating problems, like the unit not heating a home, or, a central AC blowing warm air, leaky ducts are particularly noticeable. Of course, this is because ducts are hidden, but, if you begin to notice longer periods of time to heat or cool your home, or, the airflow is weak, you might have a duct leak problem.

Ducts that leak heated air into unheated spaces can add hundreds of dollars a year to your heating and cooling bills. Insulating ducts in unconditioned spaces is usually very cost-effective. If you are installing a new duct system, make sure it comes with insulation. Sealing your ducts to prevent leaks is even more important if the ducts are located in an unconditioned area such as an attic or vented crawlspace. If the supply ducts are leaking, heated or cooled air can be forced out of unsealed joints and lost. In addition, unconditioned air can be drawn into return ducts through unsealed joints. —U.S. Department of Energy

Start by filling a water bottle with water and some liquid soap and then grab a flashlight; turn the system on and access the ductwork after. (Be sure to set the fan to the “ON” position, instead of the “AUTO” position so the system will continue to run as you hunt down leaky ducts.) You’re looking for signs such as condensation, discoloration, and visible tears as well as holes. Feel for air escaping along the ductwork and spray soapy water to pinpoint the source. You might even see metallic foil tape flopping about, a sure sign of a leak. To repair HVAC ductwork leaks, do the following:

  • Fix loose flex connections. If you notice loose flex connections, it could be due to failed a Panduit strip, which is a plastic zip tie that holds the inside and/or outside part of the connection in-place. Should the Panduit strip be frail or broken, you’ll have to replace it to reestablish a good connection.
  • Apply metallic foil tape. For connections with loose or ripped tape, you should remove the old affected portion carefully and then wrap a special metallic foil tape around the ductwork. While you might be tempted to use duct-tape, this isn’t a good solution for the application because the adhesive won’t stick for long.
  • Brush on a coat of duct mastic. After applying metallic foil tape to the ductwork, brush on a coat of duct mastic, following the manufacturer’s instructions. This will improve the seal and prevent the metallic foil tape from coming loose.
  • Let dry and then test. Let the duct mastic dry as long as recommended by the manufacturer, then, check the seal to ensure that isn’t not leaking air.