My wife and I are getting quotes for a new furnace and AC for our c. 75 year old house here in Toronto.

Its a two story with full finished basement, gas heat.

Both quotes (getting one more) have been ballpark of what we thought.

We have never had any problem with heating, bills are ok, but our AC never reaches the top floor, and the basement freezes. Not a unique problem, from what I read here.

The second installer recommended a single-stage furnace and I'm just wondering about his rationale (hope I get this right):

Since our top story is fed only by a split duct (only two outlets for four rooms), the air can never "decide" which room to heat/cool. For instance (relying on his little drawing here), Room A needs 45 CFM, Room B needs 45 CFM, but the ducts can only deliver 60 CFM.

I think I know what single/two-stage fans do.

I'm guessing he's recommending the single stage to "down sell", in that two-stage won't make any difference.

Any ideas?

Thanks in advance.