Dryer Vent Repair: When to Patch, Replace, or Reroute

Inspect the entire duct run from the dryer to the exterior cap. Start at the transition duct (the flexible section behind the dryer) — look for kinks, tears, or crushed sections. Move to the wall inlet and trace the rigid duct path: in unconditioned spaces like crawlspaces or attics, you can often see the duct directly. Common damage types: disconnected joints (sections that have separated from each other, dumping exhaust into wall cavities), foil tape failures (joints that were taped but have since peeled loose), holes or punctures in the duct wall, crushed flex duct (usually at 90-degree bends or where the dryer pressed against it), and prohibited material — plastic or vinyl sections that need immediate replacement regardless of visible damage.

The International Residential Code (IRC M1502) prohibits plastic and vinyl duct for dryer exhausts. These materials soften at dryer operating temperatures, accumulate lint in their ribbed interior surfaces, and melt during a duct fire rather than containing it. Aluminum foil accordion flex duct (the cheap silver flexible duct) is code-compliant as a transition duct only (max 8 feet) but not as a rigid duct replacement. Approved materials for the main duct run are rigid galvanized steel or rigid aluminum — smooth-walled, minimum 28-gauge. Semi-rigid aluminum is acceptable in limited applications where flexibility is genuinely required, but rigid is preferred. If any section of your duct is plastic or vinyl, that entire section must be replaced — patching prohibited material is not a valid repair.

Foil tape joint repair: The most common repair. Remove old tape, wipe the joint clean and dry, and apply new aluminum foil tape (not duct tape — it fails in heat). Press firmly for full adhesion. This is a 10-minute DIY fix. Disconnected joint inside accessible space: Re-connect the two sections, use sheet metal screws to secure the joint (maximum 1/2-inch screw penetration to avoid snagging lint), and seal with aluminum foil tape. Crushed flex duct: Replace the entire flex section — crushed flex cannot be reshaped to regain full airflow. Cut the section out and install semi-rigid aluminum or replace the entire transition duct. Hole or puncture in rigid duct: Small holes (under 1/2 inch) can be sealed with aluminum foil tape. Larger holes require replacing the damaged duct section. Disconnected duct inside a wall or ceiling: Requires opening the wall to access the joint — this is a professional repair unless you have drywall repair experience.

Repair makes sense for isolated damage on a duct that is otherwise in good condition: a single failed joint, a small hole, or a damaged flex transition in an otherwise acceptable rigid duct run. Full replacement of a section or the entire run makes sense when: multiple joints are failing simultaneously (indicating the duct is old and all tape is failing), the duct run is prohibited material (plastic or vinyl throughout), the duct route violates code (too long, too many bends, or venting into the attic instead of outside), or there is evidence of a previous duct fire (scorching, warped sections). Full rerouting is necessary when the current path is fundamentally non-compliant — for example, a duct that terminates in a wall cavity or attic instead of outside.

This is the single most important material decision in any dryer vent repair. Use only UL-listed aluminum foil tape (the silver metallic tape with a foil backing and peel-off liner). Cloth duct tape (grey or silver cloth) fails within months in a dryer vent environment — the adhesive breaks down from heat and humidity. White vinyl duct tape fails even faster. Aluminum foil tape maintains adhesion at temperatures exceeding 200°F, which is within the normal operating range of a dryer duct. Brands like 3M 3340, Nashua 324A, or equivalent foil HVAC tape are acceptable. The tape should be labeled for high-temperature use.

Call a professional for any repair that requires opening walls or ceilings, for full duct replacement in a complex or long run, for any situation involving a past duct fire, or if you find the duct vents into an attic or crawlspace rather than outside. A professional dryer vent technician can also identify problems that aren't visible from the accessible portions of the duct — a camera inspection of the full run reveals disconnected joints inside walls before they cause moisture damage. LintSnap's $149 service includes a full duct inspection; duct repairs are quoted separately based on what's found.