Louvered dryer vent hood on an outside wall with the damper flap open

Generic photo: The EnergySmart Academy · CC0

Long dryer vent run: when and how to add a listed dryer exhaust duct power ventilator (DEDPV), not a generic booster fan

When the equivalent length of a dryer vent goes past what the dryer maker allows, the options are to shorten or straighten the run, use a dryer rated for a longer run, or add a dryer exhaust duct power ventilator (DEDPV): an in-line fan listed to UL 705 for dryer exhaust, with a pressure switch that turns it on when the dryer runs and an indicator panel near the dryer. Count the run first: each 90 degree elbow adds about 5 ft and each 45 degree elbow about 2.5 ft. Use only a fan listed as a DEDPV, installed to its own instructions and local code; a plain duct booster is not built for lint and heat.

Cross-checked ~120 min moderateBrands: Fantech, Tjernlund, Panasonic, All

Before you start

Clean the entire run before deciding a fan is needed; a clogged run is a fire hazard with or without a fan
Use smooth-wall metal dryer duct; no vinyl, foil accordion or PVC in the run
Gas dryer: venting problems also mean CO risk; do not run a gas dryer on a blocked vent. Gas connections remain licensed-installer work

Diagnostic steps

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