How much air do typical ducts leak?
It varies widely. Some systems are tight, while others lose a substantial share of their airflow. Testing is the only way to know how your ducts perform.
Leaky ducts in attics and crawlspaces waste conditioned air and pull in dust. Sealing them properly is one of the most effective comfort upgrades available.
Ducts are supposed to carry conditioned air from the equipment to your rooms and bring air back to be treated again. In reality, many duct systems leak at seams, joints, boots and connections to the air handler. When those leaks occur in an attic, crawlspace or garage, the air you paid to heat or cool escapes into spaces you do not live in. Leaks on the return side pull dusty, humid or hot air from those same spaces into the system and spread it through the house.
Duct sealing addresses that waste directly. It is often one of the most cost-effective improvements for Ajo, AZ homes where rooms at the far end of the system never quite reach temperature, where dust keeps coming back, or where the attic is noticeably warm in winter above the duct runs.
We begin by inspecting accessible ductwork for obvious problems: disconnected sections, torn flex duct, gaps where boots meet ceilings and floors, and open seams at the air handler cabinet. Where possible, we measure leakage with a duct pressurization test. A calibrated fan pressurizes the duct system with registers sealed, and the airflow required to hold that pressure shows how much air is escaping. Measuring before and after gives you proof of the improvement rather than a promise.
For accessible ducts, we seal joints and seams with mastic, a thick paste that cures into a durable, flexible seal, or with foil tape listed for duct use. Cloth duct tape, despite its name, is not suitable because its adhesive dries out and fails over time. We seal register boots to the drywall or subfloor, reconnect loose sections, repair damaged flex duct and seal the air handler cabinet and return plenum where air commonly leaks.
For ducts hidden inside walls, floors and ceilings, aerosol-based sealing is an option. The duct system is pressurized with a sealant mist that collects at leak edges from the inside until the gaps close. It reaches leaks that manual sealing cannot, and the process includes measured leakage results. We explain when it is worth considering and when manual sealing is enough.
In homes with a furnace, boiler or water heater that uses a chimney or natural draft vent, return duct leaks near the equipment can depressurize the mechanical room and interfere with venting. Sealing those leaks improves safety as well as efficiency. We check for venting concerns as part of any sealing job and point out any issue we find.
Sealing works best on ducts that are already sized and laid out properly. If airflow problems come from undersized or badly routed ducts, sealing alone will not fix them, and Ductwork Install And Replace may be the better starting point. Homes with dust or humidity complaints often combine sealing with Indoor Air Quality Testing to confirm the improvement with measured readings.
Duct sealing can be done in Ajo, AZ any time of year, but many homeowners schedule it in spring or fall so the improvement is in place before the heaviest heating or cooling season. Attic sealing is easier for installers in moderate weather, and before-and-after leakage testing gives the most useful comparison when the system is about to see heavy use. If you are planning insulation work in the attic, sealing the ducts first is important, because new insulation often buries duct joints and makes them much harder to reach later.
Air that leaks out along the way never reaches the rooms at the end of the duct runs.
Return leaks pull dust from attics, crawlspaces and wall cavities into the airstream.
An attic that feels heated in winter or chilled in summer near duct runs is a strong sign of supply leaks.
Duct leakage forces the system to run longer to make up for lost air.
Loose connections, torn flex duct and gaps at boots are common findings during attic and crawlspace inspections.
Return leaks in crawlspaces or attached garages can draw odors and fumes into living areas.
We inspect accessible ducts, boots and the air handler for disconnected, damaged or leaking sections.
Where possible, the duct system is pressurized to measure how much air is escaping before sealing.
Loose sections are reconnected, damaged duct repaired, and joints sealed with mastic or listed foil tape.
We check that sealing has not affected combustion appliance venting and look for any other concerns.
A second leakage test shows the improvement, and we share the before and after results with you.
| Accessibility of ducts | Ducts in open attics and basements are easier to seal than those in tight crawlspaces or finished spaces. |
|---|---|
| Extent of repairs | Disconnected sections and damaged flex duct need repair before sealing, which adds time and materials. |
| Sealing method | Manual sealing covers accessible ducts. Aerosol sealing reaches hidden leaks and is priced separately. |
It varies widely. Some systems are tight, while others lose a substantial share of their airflow. Testing is the only way to know how your ducts perform.
Cloth duct tape is not suitable because it fails over time. Proper sealing uses mastic or foil tape listed for duct applications.
Hidden ducts can be sealed from the inside using an aerosol-based process that closes leaks without opening walls.
Sealing can raise static pressure slightly in some systems. We check static pressure and airflow after sealing to confirm the system is operating within its limits.
Often, yes. Return leaks draw dust from unconditioned spaces, and sealing them reduces that source significantly.
Manual sealing of accessible ducts typically takes several hours to a full day. Aerosol sealing projects usually take about a day, including testing.
Call to schedule duct inspection and sealing. We will measure, seal and show you the difference in numbers.
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