We are going to finish off an 800 s.f. attic space. There is a hydro air air handler in the space now that serves the second floor (also 800 s.f.).
What will be more efficient? Option 1 is upsizing the current air handler and outdoor condenser and using zone valves to provide separate zones for second floor and attic. Second floor now is served by a 2 ton system and works fine. Upsizing takes us to 3.5 ton and we are concerned that it may be too much for just one area when a single area calls and therefore inefficent.
Option 2 is to just install a separate air handler and condenser for the attic space. The issue is running hot water lines from the basement to the attic as well as ending up with a fourth ahu and condenser.