A hole in the return plenum pulls in air from a vented attic for “fresh air” [Photo courtesy of Bruce Kitchell]
![A hole in the return plenum pulls in air from a vented attic for "fresh air" [Photo courtesy of Bruce Kitchell]](https://www.energyvanguard.com/wp-content/uploads/2016/11/filter-over-plenum-hole-ventilation-air-intake.jpg)
