When I put in a new bedroom, the builder tried to convince me that an air "return" duct wouldn't be necessary if I had a half inch gap under the door. He said it was common practice for small bedrooms, bathrooms, and large closets. Since this wasn't a particularly small bedroom, I insisted on a return duct anyhow, but a door gap could work pretty well as a ventilation intake for a closet.
There are all sorts of exterior vent caps for kitchen stove exhausts, bathroom fans, and clothes dryer exhausts. Many of them are designed with a spring loaded trap door that opens when the fan blows air onto it. Some also have special shapes with turns that act as traps for foreign material. They also have screens to prevent insects and pests from getting in.
There are all sorts of exterior vent caps for kitchen stove exhausts, bathroom fans, and clothes dryer exhausts. Many of them are designed with a spring loaded trap door that opens when the fan blows air onto it. Some also have special shapes with turns that act as traps for foreign material. They also have screens to prevent insects and pests from getting in.