These units are activated automatically by negative pressure in the barn. A frictionless Styrofoam flap on a PVC continuous hinge swings down, accessing the main room to clean attic air. Flap has adjustable counter-weight to regulate air flow.

Bottom part of housing is insulated to minimize condensation, dripping, or freezing. Ideal for use in combination with recirculation ducts. All Inlets are constructed with removable insulation stops.