Will adding a cool air return in the basement help with summer AC power usage?
Furnace installers and/or home owners will put a registers in the duct work to provide some heat or A/C to that area. The number of these supply and return registers is determined by the typical use and desired temperature of this area. I recommend that all basements should have at least 2 supply registers and 1 return register in the basement/equipment area just to keep that area slightly warm or cool and the air fresh. If you are going to finish that area to be used as living space, then more supply and returns will be needed. Also you may want to close the supply registers in the summer when using the A/C since cold air is heavy and will move to the lowest level in the house. Leave the returns (mounted at the floor level) open to circulate that air all the time.