Glossary
Duct leakage
Duct leakage is the loss of conditioned air through poorly sealed joints, loose connections or tears in the ducts that carry air from the equipment to each room. When ducts run through a hot attic, as in most Florida homes, that cold air is lost and the unit runs longer to make up for it. It is measured with a pressurization test, not by eye.
What duct leakage is
Your air conditioner cools air at the unit and pushes it through ducts to the registers. If the ducts have gaps, some of that air escapes before arriving. On the return side the opposite happens: the system pulls attic air (hot, humid, dusty) instead of house air. The result is that rooms take longer to cool, the unit runs more, and indoor humidity climbs.
It is detected with a duct leakage test (duct blaster): the system is pressurized and the escaping air is measured. That number tells you whether to seal, repair or replace.
Why it matters in Florida
In Florida, ducts almost always run through the attic, which in summer can be far hotter than the house. Every cubic foot of cold air leaking there is money lost, and every cubic foot of attic air entering through the return is heat and moisture the unit has to treat again. It is one of the most common causes of “the AC can’t keep up” in homes with a perfectly good unit.
Sealing ducts costs less than replacing the equipment and usually returns more than a higher SEER. It also reduces the Manual J load, which may allow a smaller unit when replacement time comes.
Common mistake
Replacing the air conditioner with a bigger or more efficient one without testing the ducts. The new unit pushes the same air through the same gaps. Another frequent mistake is sealing with gray “duct tape,” which peels off in attic heat; proper sealing uses mastic or purpose-made foil tape. How to request the test and what to do with the result is in leaky ducts.
Full guide: Leaky ducts: the 20-30% of your cold air that goes into the attic →
Updated