Duct sealing is usually worth it and duct cleaning usually isn’t: in North Carolina most ductwork runs through vented crawlspaces and hot attics, where typical systems leak 15–30% of the air they move, so sealing joints and boots (with mastic, mesh, foil tape or aerosol sealant) commonly cuts heating and cooling use by 10–25% and improves humidity and comfort; duct cleaning removes dust that would mostly have stayed put and, outside of mold, pests, construction debris or restricted airflow, has little measurable effect on air quality or efficiency.
Why leaks matter here
Supply leaks push conditioned air into the crawlspace or attic; return leaks pull in hot, humid, dusty air from those spaces. Both make the system run longer, and return leaks are a direct cause of the humidity problems common in NC homes. Ducts also lose energy through thin or missing insulation in a 130°F attic. Leaks concentrate at joints, at boots where ducts meet floors and ceilings, at the plenum, and at flex-duct connections that were never sealed or have pulled apart.
Signs your ducts leak
Rooms that are always harder to heat or cool; dust streaks at supply registers; a musty smell when the system starts (crawlspace air); higher bills than similar homes; and, most reliably, a look in the crawlspace or attic: disconnected runs, crushed flex, gaps at boots, cloth tape that has dried and fallen off. A duct leakage test quantifies it.
Sealing options and costs
| Method | What it is | Typical cost | Notes |
|---|---|---|---|
| Manual sealing (mastic + mesh, foil tape) | Technician seals accessible joints, boots, plenum | $500–$1,500 | Best value where ducts are reachable |
| Aerosol sealing (e.g., Aeroseal) | Sealant sprayed inside pressurised ducts seals leaks from within | $1,500–$3,000 | Reaches leaks you can’t; measured before/after |
| Insulating exposed ducts | Wrap or replace poorly insulated runs | $300–$1,500 | Attic and crawlspace runs |
| Duct replacement | New system when ducts are undersized, crushed or deteriorated | see ductwork replacement cost | Often paired with equipment replacement |
Sealing typically pays back in two to five years on energy alone and immediately in comfort. It’s also required in some jurisdictions for new systems (duct leakage testing) and it improves the performance of any new equipment you install.
Duct cleaning: when it’s worth it
Do it if you have visible mold growth in ducts (confirmed, and after fixing the moisture source), a rodent or insect infestation, heavy debris after a renovation, or restricted airflow from buildup. Skip it as routine: studies haven’t shown routine cleaning improves air quality or efficiency, and the “$99 whole house” offers are typically upsells to sanitising sprays and unnecessary services. If you do clean, use a company that follows NADCA practices, seals access holes properly, and doesn’t spray biocides without cause. Better dust control comes from filters and sealed returns.
Order of operations
Seal first, then insulate, then consider equipment. Sealing shrinks the load a new system has to meet, which sometimes means a smaller (cheaper, better-dehumidifying) unit at replacement. It’s also one of the higher-payoff items when you’re chasing a high electric bill. Every contractor on the North Carolina registry shows the license status we found; ask whether they test duct leakage and what sealing method they use.