Heating & Cooling · Repair, replace or choose · Updated November 2026
Duct Sealing vs. Duct Replacement
Leaky ducts waste heated and cooled air, often into attics and crawl spaces. Many duct systems can be sealed; ducts that are crushed, badly undersized or contaminated usually need replacing.
Costs
| Option | Typical cost |
|---|---|
| Minor duct repairs | $200–$700 |
| Manual duct sealing (mastic and tape at joints) | $400–$1,900 |
| Aeroseal (sealant blown through the ducts from inside) | $1,300–$2,700 |
| Ductwork installation or replacement | $10–$40 per linear ft. |
| Full ductwork replacement (whole house) | About $3,500 average |
Sealing, repair and per-foot costs from HomeAdvisor; full replacement from our HVAC cost guide.
How leaks are diagnosed
A duct leakage test pressurizes the duct system and measures how much air escapes. Combined with a visual inspection, it shows whether sealing will help. Ask for before-and-after test results.
Sealing usually makes sense when
- Ducts are in good shape but leak at joints and connections.
- Ducts are mostly hidden in walls and ceilings, where replacement would be costly (Aeroseal can reach these from inside).
- Airflow is reasonable at most vents.
Replacement usually makes sense when
- Ducts are crushed, torn, disconnected or falling apart, especially old flex duct in attics.
- Ducts are undersized for the system and rooms are uncomfortable (uneven temperatures).
- There is mold or pest contamination inside the ducts.
- You are changing the layout or adding a system (AC with existing ducts).
Sources
- HomeAdvisor: Ductwork installation cost, accessed November 2026
Cost figures are national ranges from the sources listed above and in our heating & cooling cost guide, not a quote from FixFinch or any contractor. Calls connect you with an independent service provider in our network. FixFinch is not a contractor and does not perform the work.