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Leakage diagnosis and quote scope
Estimate manual or aerosol duct sealing while keeping leakage treatment separate from crushed runs, missing returns, wet insulation, contamination, and other repairs.
Direct answer
Duct sealing usually costs about $450-$1,500 per system for accessible manual mastic work or $1,200-$2,500 per system for aerosol sealing. Testing, crawl-space or attic access, disconnected runs, and insulation repair add cost. Sealing treats leakage; use the air duct repair guide for damaged sections and the replacement calculator for widespread failure.
Define success before work starts
A leakage number is meaningful only when the test boundary and method are stated. Do not compare a whole-house blower-door result with a duct-system leakage test as though they measure the same thing.
| Stage | Written deliverable | Decision it supports |
|---|---|---|
| Before | Test boundary, equipment status, baseline leakage, visible defect list, and excluded sections | Confirms whether leakage is material and whether repairs must happen first. |
| During | Photos or work log for boots, plenums, takeoffs, seams, access openings, and equipment protection | Shows that the quoted method reached the promised surfaces without covering damage. |
| After | Same-method leakage result, stated reduction, remaining leakage, airflow or static-pressure checks, and warranty | Separates verified performance from a material-only invoice. |
There is no universal homeowner leakage percentage that automatically means “seal” or “replace.” Use the test result with duct condition, location, airflow, moisture, contamination, and repair access. If the ducts are sound but uninsulated, price duct insulation separately.
| Method | Planning range | Best-fit scope | Evidence to request |
|---|---|---|---|
| Manual mastic or approved foil tape | $450-$1,500 per system | Accessible boots, plenums, takeoffs, seams, and visible joints | Photos or scope list plus optional before-and-after leakage test |
| Aerosol duct sealing | $1,200-$2,500 per system | Distributed small leaks, including less-accessible sections, after major openings are repaired | Machine-generated pre/post leakage report and stated reduction |
| Manual preparation plus aerosol | $1,600-$3,500+ per system | Systems with visible defects and remaining distributed leakage | Repair list, protection steps, pre/post result, and exclusions |
Diagnosis before treatment
A comfort complaint can have several causes. A useful proposal explains why sealing is the chosen remedy and what remains outside its scope.
| Observed symptom | Next check | Reason |
|---|---|---|
| High utility use but rooms are comfortable | Test leakage and equipment performance | Leakage may be one factor; runtime, insulation, weather, and equipment efficiency also matter. |
| One weak room | Inspect that branch, register, and room load | A crushed run, closed damper, undersized branch, or load problem will not be solved by sealing alone. |
| Dust or attic odor near supply registers | Inspect return and supply leakage plus filtration | Negative return leaks can pull contaminants in; identify the pathway before choosing a treatment. |
| Condensation or wet insulation | Find moisture and temperature cause first | Sealing over wet or contaminated material can conceal a larger problem. |
Crushed flex duct, collapsed liner, missing returns, unsupported runs, standing water, mold or pest contamination, asbestos-containing material, and unsafe combustion conditions need diagnosis before sealing. A lower sealing price is not a substitute for corrective scope.
Opens our partner's form on this page. Information goes directly to the partner. We may receive compensation if you submit a request. Availability varies by area.
Duct sealing commonly costs about $450-$1,500 per HVAC system for accessible manual work, while aerosol sealing often costs about $1,200-$2,500. Combined preparation, difficult access, testing, and separate duct repairs can raise the total.
It can be useful for distributed leaks that are difficult to reach, provided large openings and damaged ducts are repaired first. Value is easier to judge when the quote includes a pre/post leakage report, target, equipment protection, and exclusions.
A homeowner may be able to seal a few safe, accessible joints with appropriate mastic or approved foil tape. Avoid ordinary cloth duct tape. Stop if access is unsafe or if ducts are damaged, wet, contaminated, poorly supported, or near equipment requiring professional service.
Not always. Sealing reduces leakage but does not correct undersized returns, crushed ducts, closed dampers, poor layout, excessive static pressure, or an incorrectly sized HVAC system. Diagnose the cause first.
Testing is valuable when the contractor promises a leakage reduction or when the work is part of an efficiency project. The proposal should identify the test method, baseline, target, accessible scope, and post-work result.
The calculator separates sealing method, number of systems, access, testing, and visible repairs. The ranges are homeowner planning estimates and do not predict savings or guarantee a leakage reduction. Compare at least three scopes using the same test boundary, baseline, and target. Last updated September 29, 2026.