Considerations for extending cold-air return
I have a relatively modern energy star rated Carrier furnace/AC installed in an unfinished basement. I am thinking about finishing the basement and have had a few contractors in for quotes. One mentioned that I could make things more functional if I were to consolidate my utilities. This means moving the furnace (again). Apparently, this general contractor has an HVAC guy that would do this but I was wondering if anyone here can comment on the implications of extending the cold air return ductwork? The existing return is within the joist cavities and the new route would be about 12' longer, involve dipping below one load-bearing beam in one location, but otherwise still utilize the joist cavities.