“How would anyone know whether my ducts are leaking?”
The test
The duct system is sealed at the registers and pressurised with a calibrated fan. The fan measures how much air it has to keep pushing in to hold the ducts at a set pressure. That volume is the leakage.
It produces a number rather than an impression, and the number can be re-measured after sealing to show what the work achieved.
Why leakage matters more than it sounds
Supply leakage in an unconditioned space is conditioned air you paid to heat or cool, delivered to an attic or crawlspace. Return leakage is the reverse — the system pulls in attic, crawlspace or garage air and distributes it through the house.
Return-side leakage is the one worth caring about beyond the energy cost, because of what it pulls in with the air: dust, humidity, and in a garage, combustion by-products.
What gets corrected
- Sealing joints, seams and connections with mastic rather than tape alone
- Reconnecting duct runs that have separated
- Replacing crushed or kinked flexible duct
- Sealing the plenum and the cabinet where they meet
- Re-testing afterwards so the improvement is measured, not assumed
Testing is not cleaning
Duct testing, sealing, renovation and airflow measurement are different work from duct cleaning, and GV's does the former. If what you want is duct cleaning, that is not a service offered here.