I have a 900 sq ft ranch w/basement home that I am remodeling. The furnace is a propane forced air and is located down stairs. I had two cold air returns upstairs and have closed one of them off. This has not seemed to have hurt the heating/furnace at all. I do not have a cold air return from the down stairs area. My question is can I leave the one cold air return closed off upstairs and should I add a cold air return downstairs?

No return air should ever be closed off because it draws air from different parts of the house. You can install a return air down stairs but it is not recommended unless you also supply combustion air for the furnace.

No return air should ever be closed off because it draws air from different parts of the house. You can install a return air down stairs but it is not recommended unless you also supply combustion air for the furnace.

As I tore out a bedroom wall the returns upstairs are pretty close together. I do have a louvered door for furnace room and there is outside air (thru vent and pipe) coming into the furnace room. If it would be OK where would you install a downstairs cold air return?

You would want to try and keep it away from the furnace area to prevent the RA from interfering with the flow of air for combustion.