I can help you out with that one. I worked in the HVAC field for 10 years and now have been in the instrumentation field for 17years. It would be best to have the cold air return to the furnace near the floor if you want to go through that extra work, however, having the a cold air reutrn as far away from the furnace as far as practical is great. If it is at the ceiling that is ok. Your just trying to get some circulation. Another option is if your furnace room is centrally located in the basement, that a grill in the door is fine. How big is the basement and how open is it? I imagine you probably have two return air grills up stairs? Also, one other option that I recommend is a two speed fan motor if you have any problems with cold spots, sickness, or moisture. Anyway, email me if you like and we can talk more.
Thanks,
Gerry
