Signs Your Ducts Leak or Underperform
ENERGY STAR estimates that a typical house loses about 20 to 30 percent of the air moving through its ducts to leaks, holes and poorly connected runs. It lists these warning signs:
- High utility bills in both summer and winter
- Rooms that are hard to heat or cool
- Stuffy rooms that never feel comfortable
- Ducts that run through an attic, crawl space or garage
- Tangled or kinked flexible ducts
Leaky return ducts cause one more problem: they pull attic insulation, crawl space dust and garage fumes into the air stream. Cleaning without sealing those leaks just resets the clock.
How Technicians Inspect Ductwork
| Method | What it finds | What it misses |
|---|---|---|
| Visual check with a flashlight | Loose joints, damaged insulation and crushed flex duct in accessible areas | Anything inside walls, ceilings and duct runs |
| Inspection camera | Debris, mold, pests and disconnections inside runs | How much air the system actually loses |
| Pressure leakage test | Total air leakage from the whole duct system | The exact location of each leak |
| Room-by-room airflow check | Registers delivering too little air | Why the airflow is low |
A thorough inspection combines at least the first two. Read what a full air duct inspection covers and what the footage should show.
Seal, Repair or Replace
| Problem | Fix |
|---|---|
| Leaky seams and joints | Seal with mastic sealant or metal foil tape |
| Boot pulled away from the register opening | Reconnect and seal |
| Kinked, sagging or crushed flex duct | Re-support or replace the run |
| Torn or missing insulation on attic ducts | Repair and insulate |
| Wet or moldy duct insulation | Replace — the EPA says it can't be cleaned |
Sealing leaks is not the same as spraying sealant inside ducts
Sealing the outside of joints saves energy, according to ENERGY STAR. Spraying encapsulants inside ducts to coat dirt is a different practice the EPA, NADCA and other industry groups don't recommend for routine use. Learn the difference on the air duct sealing page.
Start Where the Ducts Are Unconditioned
ENERGY STAR advises sealing and insulating every duct you can reach in attics, crawl spaces, unfinished basements and garages. Those spaces get hotter, colder or damper than the house, so a leak there costs the most. In Dulles-area townhomes and upper-floor systems, that usually means the attic — see attic ductwork.