this 4 dryer vent seal has a floating shuttle that stays closed unless there is a load of clothing drying. A positive seal keeps cold or hot air out as well as unwanted pests. how to seal a dryer vent pipe: Medium to large gaps. For filling larger vent gaps, foam is the best choice. when the clothes dryer or bath fan operates, the exhaust air pressure pushes the damper to let the exhaust air escape from the vent. You can easily use the exhaust vent for new.
