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NC State Extension

Air Sealing and Insulation: Ductwork

Term – Air Duct – A hollow conduit or tube (square or round) that circulates air from a forced-air heating and/or cooling system to a room (supply duct) or returns air back to the main system from a room (return duct).

Air ducts:

Here is a very helpful video about the importance of sealing air ducts. WSU Extension Energy Program’s Energy Experts provide this informative video on sealing your HVAC system ducts. This is an extremely cost-effective energy efficiency action that also improves indoor air quality. This video shows how ducts move air, where common leaks are, and shows how to fix them. The video is for building professionals or do-it-yourself homeowners. Even if you aren’t planning to do the work yourself, this video shows why it is important to have it done.

In houses with forced-air heating and cooling systems, ducts are used to distribute conditioned air throughout the house. But in typical houses, about 20% of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts. The result is higher utility bills and difficulty keeping the house comfortable, no matter how the thermostat is set. Some signs that a home may have leaky, poorly insulated, or inefficient ducts:

  • High summer and winter utility bills;
  • Rooms that are difficult to heat and cool;
  • Stuffy rooms that never seem to feel comfortable;
  • Ducts are located in an attic, unfinished basement, crawlspace, or the garage;
  • Tangled or kinked flexible ducts in the system.


Because ducts are often concealed in walls, ceiling, attics, and basements, repairing them can be difficult. But there are things that you can do to improve duct performance in your house. Start by sealing air leaks using mastic sealant or metal tape and insulating all the ducts that you can access. Never use duct tape, as it is not long-lasting. Also, make sure that the connections at vents and registers are well-sealed where they meet the floors, walls, and ceiling. Read about common issues found in ductwork.

Common Duct Problems:

  • Leaky, torn, and disconnected ducts
  • Poorly sealed registers and grills
  • Leaks at furnace and filter slot
  • Kinks in flexible ductwork restricting airflow
  • Make sure the duct system is not leaky, crimped, blocked, wet, moldy, damaged, etc.
  • Look out for crimped (restricts air flow):
    • Leaky (do NOT use duct tape to seal ducts)

Images of ductwork:

Screen Shot 2014-06-07 at 6.47.12 p.m.   Screen Shot 2014-06-07 at 6.44.46 p.m.

Screen Shot 2014-06-07 at 7.10.53 p.m. Screen Shot 2014-06-07 at 7.09.36 p.m.

Screen Shot 2014-06-07 at 6.53.54 p.m.

Page Last Updated: 5 years ago
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