· by Michael Blair, Nashville's Air Duct Cleaning
Most Nashville houses run ductwork through a crawl space or attic — unconditioned space. Any air escaping there is conditioned air you paid for, delivered to somewhere you are not trying to condition.
Where ducts leak
At joints and connections, at the plenum, at boot connections to registers, and wherever flexible duct has come loose or torn. Older systems sealed with cloth duct tape leak badly, because that tape fails within a few years.
The name is misleading — duct tape is the one product not suitable for sealing ducts.
What sealing involves
Mastic, a paste applied over joints and connections, or foil tape rated for the purpose. Mastic is the durable answer and it is not an attractive job in a crawl space, which is why it gets skipped.
Aerosol sealing from inside the ducts exists and works well where access is genuinely difficult.
- Mastic or rated foil tape, never cloth duct tape
- Seal boot connections at registers, commonly missed
- Insulate ducts in unconditioned space after sealing
- A blower door and duct test quantifies it
- Return leaks pull crawl space air into the house
Return leaks matter most
A leak on the supply side loses conditioned air. A leak on the return side pulls unconditioned crawl space or attic air into the system and distributes it through the house.
In a Middle Tennessee crawl space that means humid, sometimes musty air being drawn into every room. It is an air quality issue as well as an energy one.
Insulating after sealing
A sealed duct running through a 130-degree attic still loses heat through its walls. Insulation on the duct addresses that, and it should follow sealing rather than replace it.
Sealing then insulating is typically the highest-return HVAC work available in a Nashville house.