Patent ID: 8021217

Claim:
A self-contained pre-manufactured air unit for installation on a roof top of a building for circulating air through said building, said unit comprising a housing having a blower therein, said blower being connected into a circulation system comprising a first air outlet for flowing air to the building and a second air inlet for returning air from the building to circulate air into and out of said building, said unit having a pressure relief opening for connection to said building, said pressure relief opening being separate from said second air outlet and said first air inlet, and being independent of said blower such that a vacuum created by the blower within the housing does not affect a pressure in the pressure relief opening, wherein the pressure relief opening is connected to exhaust air from said building to ambient air when air pressure within said building exceeds a pressure of said ambient air; said pressure relief opening is connected via a duct to an exhaust vent in said unit, said exhaust vent having a damper that opens automatically when said air pressure within said building exceeds a pressure of said ambient air and closes when the air pressure within said building does not exceed a pressure of said ambient air.