I am in the process of designing a 2nd floor addition to my 1500 sf ranch. The current forced hot air, gas furnace is in the basement. I plan on having it replaced with a new Trane with central air. Will I be able to have one unit to heat/cool the 1st and 2nd floor? Can I have the duct work extended up through the 2nd floor into the attic and branch off to the seperate rooms from there? Or, will I have to have 2 seperate HVAC units, 1 for each floor? I am estimating $10-15K, am I in the ballpark? Any comments/suggestions would be appreciated.