I just bought an old Victorian house with a boiler system for heating. I'd like to replace the system with a gas furnace/central air. I'd like to damage the plaster as little as possible. I'm thinking maybe a dual zone system is the way to go. I was thinking I could run the ductwork for the upstairs in the attic and the ductwork for the mainfloor in the partial basement/crawlspace. What are your thoughts? Also, what are your thoughts on replacing the old windows vs. weatherstripping/refurbishing? They are in pretty good working order, I'm just wondering what would improve resale the most.