I am considering replacing an old 80 percent efficient, single stage furnace with a high efficiency, two-stage unit. I am also considering moving up to a two-stage furnace with a VSD. My question is two fold: (1) Is the VSD unit worth the investment in terms of potential electricity saved? I do have central air that does not run all summer, since I live in Buffalo, NY. (2) What is the anticipated life-span of a VSD blower motor and what is a rough cost of replacement should a motor fail? Thank you.