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 re-circulation ducts. All Inlets are constructed with removable insulation stops.