US Patent 7565924 Pressure equilizing system

An air handling system for an indoor space comprising a first forced indoor air treatment component, an input indoor air duct element and an output treated air duct element respectively coupling said first forced indoor air treatment component to said indoor space, a second forced air treatment component a stale air duct element coupled to said second forced air treatment component and to said input indoor air duct, a return air duct element coupling said second forced air treatment component to said output treated air duct element characterized in that said system comprises a secondary air path means for coupling said return air duct element to said input indoor air duct element.