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Are you talking about combustion air or room air return?

Ideally combustion air should come from the outside although with older furnaces this is difficult to accomplish other than by walling off the furnace into a separate smaller room.

The room air return should be from inside the house and not draw from a basement not used as living space with heated air registers. Some elaborate return duct systems have an adjustable outside air inlet but for most residential situations fresh are is gotten from a slightly open window rather than via such a system.
 
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