You can easily use the exhaust vent for new. For filling larger vent gaps, foam is the best choice. Webthis 4 dryer vent seal has a floating shuttle that stays closed unless there is a load of clothing drying.

Webwhen the clothes dryer or bath fan operates, the exhaust air pressure pushes the damper to let the exhaust air escape from the vent. A positive seal keeps cold or hot air out as well as unwanted pests. Medium to large gaps.