Dryer Vent Inspection: How to Assess Your Vent System

A vent cleaning is a service: you pay someone to remove lint from the duct. An inspection is an assessment: a systematic evaluation of every component of the vent system. Cleaning doesn't require checking duct material, measuring duct length, counting bends, or evaluating the exterior cap type. A cleaning tech who also inspects will tell you if the duct is prohibited material, if the run is too long, or if the cap design creates a fire or pest hazard. LintSnap includes a basic inspection as part of every $149 cleaning visit — confirming cap condition, transition duct type, and exterior airflow. A full code-compliance inspection goes deeper and may be quoted separately for complex systems.

The exterior vent cap is the first and last point of your vent system. During a cycle, the cap flap should open fully — open it and observe it from outside while the dryer runs. A flap that only partially opens indicates restriction in the duct. After the cycle, the flap should close completely — a flap stuck open allows pests and cold air to enter. Look for: (1) Broken or missing flap — requires cap replacement. (2) Bird nest at or inside the cap — requires removal and flap replacement. (3) Ice buildup in winter — indicates the flap is not sealing when closed, allowing cold air in and causing condensation to freeze. (4) Pest screen or mesh on the cap interior — mesh caps may seem like they keep pests out, but they accumulate lint rapidly and create a blockage hazard. Replace mesh caps with a proper louvered or single-flap cap.

Pull the dryer out and inspect the transition duct (the flexible section between the dryer and wall inlet). Check for: material type (plastic or vinyl = replace immediately), kinks or crushes (replace if the diameter is compromised), length (maximum 8 feet), and secure connections at both ends. The transition duct should not be coiled, kinked, or running through any wall or cabinet opening. A properly installed transition duct has a gentle curve and runs at full diameter from dryer exhaust port to wall inlet. Look for foil tape or clamps at both connection points — missing tape means the joint may be leaking exhaust into the space behind the dryer.

The rigid duct inside the wall, floor, or ceiling requires inspection at all accessible points — typically where it enters unconditioned spaces like attics, crawlspaces, or basements. Check for: (1) Material — smooth rigid aluminum or galvanized steel is correct; corrugated foil is acceptable only as transition duct, not rigid duct replacement. (2) Joints — all joints should be mechanically connected (screws or slip joints) and sealed with aluminum foil tape. Unsecured or taped-only joints can separate over time, dumping exhaust into wall cavities. (3) Bends — count the elbows. Each 90-degree elbow reduces the effective duct length by 5 feet (per IRC M1502). With a maximum 35-foot equivalent length, four 90-degree elbows consume 20 feet of allowance before the straight runs. (4) Length — estimate or measure the total run. If the equivalent length exceeds 35 feet, the system is non-compliant.

Certain inspection findings require stopping dryer use immediately until corrected: (1) Duct terminates inside the attic, crawlspace, or garage — this is prohibited and introduces moisture and fire risk into the structure. (2) Plastic or vinyl duct anywhere in the run — prohibited material must be replaced before running the dryer again. (3) Visible duct fire damage — scorching, melted sections, or warped metal indicates a previous duct fire; the duct must be inspected by a professional and likely fully replaced. (4) Completely blocked exterior cap — no airflow means no safe dryer operation. (5) Gas smell during inspection — stop everything and call the gas utility.

Inspect the transition duct and exterior cap visually every 6 months — these are the easiest and most frequently problematic components. Full system inspection (including accessible rigid duct sections) annually, ideally combined with professional cleaning. Inspect before and after any dryer moves or reinstallation. When buying a home, request a dryer vent inspection as part of the home inspection or schedule one separately — home inspectors often flag duct length and material issues, but they rarely do a full code-compliance evaluation.