Exhaust ventilation systems work by depressurizing the building and lowering the inner air pressure to below that of the outside air. The stale air is sucked out of the building via an exhaust mechanism and a ducting system on the exterior. Fresh air is then introduced from a separate source, generally another air vent.
They're most often installed in the bathroom, kitchen, foundation, crawl space or utility room. Prevent a build-up of steam, humidity, cancer-causing radon gas and reduce mold growth and termite infestation. Although bigger rooms or space may require extra systems, it is most beneficial to place them in localized locations near where dampness builds up.