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Air distribution or duct systems are designed to supply rooms with air that is “conditioned”—that is, heated or cooled by the heating, ventilation, and air conditioning (HVAC) equipment—and to recirculate or return the same volume of air back to the HVAC equipment. Your duct system has two main air transfer systems: 1) supply, and 2) return. The supply side delivers the conditioned air to the home through individual room registers. The return side picks up inside air and delivers it to the air handler of your central system where heat and moisture are either removed or added and then delivered to the supply side. All of the air drawn into the return duct(s) is conditioned and should be delivered back through the supply registers.
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April 3, 2020