I have 2 return air vents, 1 on the floor that will open and close and on about 4 inches from celing. The bottom vent should be open or closed fro heating?
Thanks for your help

Open because you want the cooler
Air at floor level to get sucked into the system

And leave the warm air in the room

And close it for ac operation to suck the warm air off the ceiling

Check out this thread from several days ago. https://www.askmehelpdesk.com/heating-air-conditioning/heating-system-we-have-air-vents-walls-our-home-281257.html