Is Duct Sealing Worth It?
For most homes with ducts outside the living space, yes. ENERGY STAR puts typical duct losses at 20 to 30 percent of the air the system moves, which shows up as higher bills and rooms that never feel right. Sealing goes straight at that loss.
Measure it. A duct leakage test before and after sealing shows exactly how much air you got back.
Mastic, Metal Tape or Duct Tape: What Holds Up
| Material | Where it works | Verdict |
|---|---|---|
| Mastic sealant | Seams, joints, boots and irregular gaps | Recommended by ENERGY STAR |
| Metal tape | Straight seams and flat joints | Recommended by ENERGY STAR |
| Cloth duct tape | Nowhere on ducts | Avoid — not long-lasting, per ENERGY STAR |
Joints Worth Sealing First
- Connections where registers meet floors, walls and ceilings, which ENERGY STAR names as common leak spots
- Joints on ducts in the attic, crawl space, unfinished basement or garage
- The connections at the air handler and filter box, which Virginia's code requires sealed
- Disconnected runs, which need ductwork repair before any sealant goes on
From Dusty Seam to Sealed Joint
Find the Leaks
An inspection or leakage test shows which joints matter.
Clean the Surface
Mastic and tape grip poorly on dust, so the seam gets wiped first.
Refasten Loose Sections
Screws or clamps hold the joint; sealant alone doesn't.
Apply Mastic or Metal Tape
Brush mastic over the seam, or press metal tape flat along it.
Insulate Exposed Ducts
ENERGY STAR advises insulating ducts you can reach in attics, crawl spaces, unfinished basements and garages. Attic runs get extra attention on the attic ductwork page.
Retest
A second leakage reading confirms the work.
Sealing Joints Isn't the Same as Coating Duct Interiors
Some cleaning companies offer to spray a sealant coating inside ducts after cleaning. That's a different product with a different purpose. The EPA reports that it, NADCA and other groups don't recommend the routine use of sealants to cover the inside of ducts. Leak sealing works on the joints and seams, where the air actually escapes.
Aerosol Duct Sealing (Aeroseal) for Leaks You Can't Reach
Aerosol duct sealing is a third, separate method, and it works from the inside without coating the whole duct. A technician blocks the registers, pressurizes the duct system with a calibrated fan and injects sealant particles. The particles stay airborne until they reach a leak, then build up at its edges until it closes.
Lawrence Berkeley National Laboratory developed the technique with funding from the Department of Energy and the EPA, and reports that it seals 70 to 90 percent of duct leaks. Its advantage is reach: it finds leaks in ducts buried behind finished walls and ceilings, where hand sealing can't go. Aeroseal is the best-known brand. Ask for a leakage test before and after, so the result is a number rather than a promise.
How Duct Sealing Is Priced
Sealing is priced by how much duct can be reached, not by the size of the house. The same 2,500-square-foot home can be a short job with an open basement or a long one with every run buried in a finished ceiling.
| Factor | Effect |
|---|---|
| Ducts in an open attic or unfinished basement | Reachable joints, faster work |
| Ducts behind finished walls and ceilings | Only the ends can be reached by hand |
| Insulation needed after sealing | Material plus labor added |
| Leakage test before and after | Adds time, but proves the result |
Ask for a camera inspection first. At $0 to $125, and often free with a booked cleaning, it shows which joints are leaking before you pay to seal any of them.
Northern Virginia market ranges reviewed in 2026, not a quote. Your price depends on vent count, system count and access.