I live in Virginia in a house built in 2002. I have a 6" pipe that runs from the outside to my cold air return. I have a propane furnace, but it is not the high efficiency kind that require a separate line into it for combustion.. I can kind of see a reason to have this in the winter time, but in the summer is it really necessary? Also, my 6" pipe is located about 2 feet from my outside AC unit. When I was having my routine maintenance done, the AC guy commented on the horrible location saying it would be pulling in even hotter air with that location. I would love to seal it up during the AC season, if possible.
Speaking of return, how do they check to see if the return ducts are pulling air adequately? I know nothing about HVAC systems, but it seems to me the last intake location in my house is not doing much.