Here's my take on it, but remember it's only a guess on my part.
The Cold air return for the furnace is the one resister located in the bottom step to the bedroom, the vent area under the entrace way coat closet and also the two vents, the one under the dresser drawers and the one in the basement ceiling
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Michelle & Ann
2018 Chevy 3500HD Crew Cab High Country DRW, D/A, 2016 RW39MB, Dual ACs, Auto Level, Auto Sat Dish, Stack W/D, King Sleep #, 17.5" Sailuns w/Disc, MORryde IS & Pin, Comfort Ride Hitch, 5.5 Onan, Res Fridge & Induction Cook Top
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