You can expect residential ducts to last 25 to 70 years, with an average of 45 years. The big spread is due to the variables of materials, workmanship, and maintenance. Flexible ducts, for example, will have a shorter life than hard ducts. They also sag over time and restrict air flow if poorly suspended. 

    A homeowner’s tolerance for energy loss due to leakage as the ductwork ages, with the resulting uncomfortable rooms and higher utility bills, is another factor that affects the determination of end-of-life.

    The EPA estimates that "about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts” in an average house. Duct leakage in return-air ducts can also have the opposite effect, sucking undesirable air from a crawl space or attic into the system.

    Having an HVAC contractor check and mastic-seal your ducts will extend their lifespan. It will definitely be necessary at about 15 to 25 years, if not sooner. A single big hole, like the one shown below, can lose a lot of air. But multiple tiny openings at duct damage, connections, and around registers, which are often virtually invisible, can add up the same amount of air loss. 

    It’s not unusual for a home inspector to recognize a ductwork problem when entering a crawl space or attic, just based on the air temperature. We were in an attic on a cold day last week that was warmer than the home below. It happens. The owner was complaining about high utility bills and a chilly master bedroom.

   Another common problem with older ducts is the damage caused by people crawling over them to do repairs or retrieve stored boxes in the attic. 

    And rodents gnawing in the attic can destroy a duct system in just a few years.

    What can you do? Have you ducts checked by an HVAC tech every few years, possibly while getting a regular checkup or other repairs on your heating/cooling appliances. Or inspect them yourself if you are able. Just don’t crawl over the ducts.  

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner?  

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.