I am a newbie to this site and I like what I have read here
. My son and I are looking very seriously to purchase an old home with gravity feed octopus furnaces (two). We are trying to estimate the cost to replace the furnaces and add central air. I will DIY all of the duct work and hire a licensed HVAC installer for the heat and air units. I completely understand the asbestos issues and can easily remove the old units. I am trying to get a better understanding of the duct work requirements. The heat ducts were placed on exterior walls, thank goodness for that. The return air ducts are on the first floor in the main living areas of the home. Can I use these return air ducts as is, or do I need to run new returns to the upstairs bedrooms?