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I have a Laundromat with a 30 year old hvac duct system. The indoor air handler and electric coil (for heat) is located in the basement. The compressor is outside in the yard.
My question pertains to the return duct. There are (2) separate fresh air ducts that tee off the return duct and terminate outside. They both have electric dampers. One fresh air duct is connected on the first floor return and the second is connected to the return directly before it enters the air handler.
Can anyone explain why this is necessary? Can I eliminate it and install indoor return grills? (I do not see any indoor return grills in the Laundromat but they might be inside the drop ceiling) The system is about 30 years old and it was originally installed for a Chase bank.