How long does ductwork last?

How long ductwork lasts depends on its condition more than a number of years: how well the joints, seals and insulation hold up, and whether the ducts stay dry and undamaged. Some homeowners take on duct sealing as a do-it-yourself project, sealing and insulating the ducts they can reach, and many work with a professional contractor, since most heating and cooling equipment contractors also repair ductwork.^[3] EPA notes that many insulated duct systems have operated for years without supporting significant mold growth, and that keeping them reasonably clean and dry is generally adequate.^[2] The parts that most often give trouble are the seals, old cloth tape, insulation and flexible duct, and moisture, crushing and a poor install all shorten their life.

What wears out, and why

Homes change as they age: tape adhesive dries out and caulking erodes.^[1] Ducts also come apart, and at the rooms, the joints where registers meet floors, walls and ceilings are common places to find leaks and disconnected ductwork.^[3] A system can look intact and still lose a lot of air at joints that were sealed decades ago.

How the material matters

Sheet metal. Round galvanized steel ducts wrapped in insulation with a vapor barrier are preferred over other duct materials, in Virginia Cooperative Extension's words,^[1] and the zinc coating on galvanized metal resists mold and is easier to clean.^[1]

Flexible duct. Flex duct has a plastic liner surrounded by insulation, often bound by a reflective covering,^[1] and it has to be pulled tight and kept free of bends and pinches for full airflow.^[1] It is easier to tear, crush or kink than metal, especially in attics where people walk and store things. EPA notes that it can be more economical to replace accessible flex duct than to clean it.^[2]

Ductboard. Rigid ductboard is rectangular, foil covered and lined with fiberglass,^[1] and is common around air handlers and plenums. Its foil facing and fiberglass are what to watch for damage and moisture.

Seals and tape. Before you touch old joints in an older home, know that EPA's rule of thumb for possible asbestos is "If in doubt, treat the material as if it contains asbestos and leave it alone."^[7] Asbestos-containing materials in a heating and cooling system, such as insulation and register boots, need specialized procedures and should be disturbed or removed only by trained and equipped contractors.^[2] In older systems, gray, rubber-adhesive cloth duct tape eventually fails because its rubber-based glue is short-lived.^[1] Virginia Cooperative Extension notes that properly applied foil tape carries a 20-year promise,^[1] and that mastic adheres well to most surfaces and provides an effective long-term seal.^[1]

What shortens duct life

Moisture. Moisture can enter the duct system through leaks or poor installation or service, and condensation on or near the cooling coil is a major factor.^[2] In a humid Virginia summer, an uninsulated duct in a hot attic or a damp crawlspace can sweat. Ducts in attics and crawlspaces need to be sealed and insulated to keep condensation out.^[2]

Once insulation is wet, the clock runs out. Insulated ducts whose insulation gets wet or moldy cannot be cleaned effectively and should have that insulation removed and replaced.^[2] Steam cleaning and other methods that use moisture should not be used on any kind of ductwork.^[2]

Crushing and sagging. Flex duct that is stepped on, buried under stored boxes or allowed to sag between supports loses airflow and eventually tears.

Pests. Rodents and insects can nest in ducts, and EPA lists ducts infested with vermin among the reasons to have them cleaned.^[2]

How to make ducts last

Ductwork should be inspected once a year for leaks.^[1] You can check the ducts you can reach yourself, using the steps on this page, and some utilities and home energy raters offer audits with blower door, duct blaster and pressure pan tests to find what you cannot see.^[1] Dominion Energy's advice is to periodically check your ductwork for leaks or tears, repair fallen or crushed ductwork, and seal leaks with mastic.^[8]

Watch for the signs ENERGY STAR lists for poorly performing ducts: rooms that are difficult to heat and cool, stuffy rooms that never feel comfortable, high summer and winter bills, and tangled or kinked flexible ducts.^[3] ENERGY STAR also notes that humidity problems and excessive dust can point to leaky or poorly insulated ductwork.^[6]

Repair or replace?

Most duct problems are repairs: resealing joints, reattaching a fallen run, replacing a crushed length of flex duct, or adding insulation. Replacement makes sense when sections have collapsed, insulation is wet or moldy, the layout never delivered enough air, or the ducts are being rebuilt with a new system. When new equipment goes in, a contractor may advise that some ducts need to be replaced or added.^[6]

Stop and call a pro if

• Ducts are collapsed, disconnected or crushed somewhere you cannot reach.
• Duct insulation is wet, moldy or smells musty, or there is standing water in the condensate pan.
• You find rodents or insects living in the ducts.
• Old duct wrap, tape or register boots might contain asbestos. Leave them alone until a trained professional tests them.
• Sections need to be replaced, added or rerouted. That is contractor work; ask your building department whether it needs a permit. See whether you need a permit to replace ductwork in Virginia.

Related

To reseal joints yourself, see how to seal leaky air ducts, and for a price picture, how much new ductwork costs in Virginia. For the equipment side, read how long an HVAC system lasts. Browse heating and cooling services, find HVAC businesses in Blacksburg, or read more heating and cooling answers.

When it is time for a repair, describe the duct job once and licensed local HVAC businesses quote it.