I'm going to get proposals on a new furnace installation, but I am concerned that my chimney cannot handle the modern furnaces. That is, I currently have a water heater and a furnace sharing the same clay lined brick chimney. I only want to replace the furnace, that is 20 years old, and the modern units I see online seem to have a fan in the vent system. Can these modern furnaces share a common chimney with a (no-vent-fan) water heater?
If a fan vent furnace cannot share a chimney are there furnaces available without that fan that could solve my problem? If I have to give up some efficiency I can live with that.
I'm trying to get prepared for the problems I am likely to hear when I get the proposals.