Duct sealing closes the gaps, open joints, disconnected boots, and torn flex that let conditioned air escape before it reaches a room, and let unconditioned attic or crawl space air get pulled into the return side of your system. It is a different job from cleaning, and it is the one that actually shows up on a power bill.
How Much Air Is Actually Escaping?
ENERGY STAR estimates that about 20 to 30 percent of the air moving through a typical duct system is lost to leaks, holes, and poorly connected sections. That is not an edge case number for badly built houses. That is the normal condition of ordinary ductwork.
Atlanta homes tend to land at the worse end of that range, and the reason is where the ducts live. Very little residential ductwork in this market runs inside the conditioned envelope. It runs through vented crawl spaces and through attics that hit brutal temperatures in July. A leak in a duct that sits inside the house is wasteful but the air at least stays in the building. A leak in an attic duct dumps cooled air into a space that is already 130 degrees, and the return-side equivalent pulls that superheated air straight into your system.
What Leaky Ducts Look Like From Inside the House
- Utility bills that climb faster each summer than your usage explains
- One or two rooms that never reach the thermostat setting no matter how long the system runs
- Weak airflow at a register that used to be fine
- Ductwork running through an attic, crawl space, or garage
- Flexible duct that is kinked, sagging between supports, or pulled loose at a boot
- A crawl space or attic smell that shows up when the system kicks on
That last one is worth its own note. If your house smells like the crawl space when the AC starts, you do not have an odor problem, you have a return leak. Sealing it fixes the smell as a side effect of fixing the actual issue.
What We Seal With, and What Nobody Should Use
Mastic sealant and foil-backed metal tape. That is the list.
Mastic is a thick, brush-applied compound that stays flexible and bonds to sheet metal, flex collars, and plenum joints. It handles the movement a duct system goes through as it heats and cools, and it fills gaps that tape cannot bridge. Metal tape, the UL-listed foil kind, works for clean straight seams on rigid duct.
What does not work, despite the name, is duct tape. ENERGY STAR says plainly never to use it, because it is not long-lasting. In an Atlanta attic the adhesive gives up faster than the average, and a seam taped three summers ago is often hanging open by the time anyone looks again. If you have had duct work done and the seams are wrapped in gray cloth tape, that is a finding, not a repair.
Where the Leaks Usually Are
Leaks are not distributed evenly. In practice they cluster:
- At the plenum. The connection between the air handler and the trunk line is where the pressure is highest and the leak is largest.
- At boot connections. Where the duct meets the register in a floor or ceiling, particularly if the boot was never sealed to the subfloor.
- At flex-to-collar joints. The inner liner pulls back from the collar over time, and the insulation wrap hides it from view.
- At old branch takeoffs. Every time a system has been modified, a room added, a run rerouted, there is a joint that may or may not have been sealed properly.
- Disconnected runs entirely. More common than people expect, especially in crawl spaces where something bumped a duct loose and nobody was under there to notice.
What Duct Sealing Costs in Atlanta
Nationally, duct sealing runs about $1 to $2 per square foot of conditioned space, with most whole-home jobs landing between $1,000 and $6,000. Aerosol-based interior sealing averages $1,500 to $6,900. Diagnostic work is separate: a duct inspection runs $150 to $500, and a pressure test $200 to $450.
What moves your number:
- How much duct there is, and where. A one-story ranch on a slab with short runs is a different job from a two-story with an attic trunk line.
- Access. A three-foot crawl space costs more in labor than a walkable basement, because everything takes longer on your back.
- Condition. Sealing good ductwork is straightforward. Ductwork that needs sections replaced before it can be sealed is a repair job with sealing attached.
- Whether you want it verified. A post-seal pressure test proves the work hit its target instead of asking you to take our word for it.
Sealing vs. Replacement: Which Do You Need?
Sealing Makes Sense
The ductwork is structurally sound, the insulation is intact, and the problem is joints and connections. This describes most homes. Sealing is the cheaper fix by a wide margin and it delivers most of the available gain.
Replacement Makes Sense
The flex is crushed or torn along its length, the insulation is degraded or wet, or the system was undersized from the start. Sealing a duct that is falling apart is money spent to delay the real repair by a season.
We will tell you which one you are looking at. It is a bad trade for us to seal ductwork that needs replacing, because you will be calling back.
Frequently Asked Questions
How much conditioned air am I actually losing to duct leaks?
ENERGY STAR puts it at roughly 20 to 30 percent in a typical house. That is air you paid to cool sitting in a crawl space or attic instead of reaching a room. Atlanta homes tend to sit at the higher end of that range because so much ductwork here runs through unconditioned attics and vented crawl spaces rather than inside the building envelope.
Can I just use duct tape?
No, and this is one of the few places where the common name of a product is actively misleading. ENERGY STAR is direct about it: never use duct tape, because it does not last. The adhesive dries out and releases within a few years, often faster in a hot Atlanta attic. Mastic sealant or foil-backed metal tape are what actually hold.
Is sealing the same thing as cleaning?
They are separate jobs that happen to involve the same ductwork. Cleaning removes what is inside the ducts. Sealing closes the gaps that let conditioned air escape and let attic and crawl space air get in. If your complaint is dust at the registers, you want cleaning. If it is high bills and a room that will not cool, you want sealing.
How do you find the leaks?
A visual inspection catches the obvious ones, disconnected boots, open joints, torn flex. Finding the rest takes a pressure test, where the duct system is pressurized and the leakage rate measured against a target. Inspection typically runs $150 to $500 and pressure testing $200 to $450. On an older home with a long history of HVAC work, the test usually pays for itself by telling us where not to spend labor.
Dealing with dust at the registers or a musty smell too? See our full list of services, or read about duct mold removal.