80% efficient furnaces are fine…they are cheaper and more reliable than 90% furnaces on average…often the 2 furnaces arent really competing…in your situation,,there is no where to run the plastic vent pipe,,so you have to vent to the exising main vent pipe or chimney..so you have to go with the 80% furnace..sometimes its the opposite…a new home may not be designed with a main vertical vent or chimney,,,or an existing chimney in an older home isnt usable and not worth fixing,,so in order to have gas heat you have to get a 90%+ furnace…… depending on the age of your furnace,,an 80% might be a decent improvement……as far as advice goes…i think the bryant evolution is the same as the carrier infinity model…its a good brand,but the thermostat is pretty complex,,no big deal for competent hvac techs or technically inclined homeowner,,but not what you want if you are a "keep it simple,,set it an leave it"kind of guy…….personally i like them,but they are not for everyone…..is your existing furnace located in a room near where you spend a lot of time,,,near tv or dining room?? if your old furnace was relatively quiet,,then you might be surprised at how much noise comes from a new furnace with their "inducers",,"inshot burners" and powerful blowers….dont get a furnace bigger than than you need,,,,one option to reduce noise is to get the bryant evolution 2-speed furnace…under most circumstances it will run on low-speed, , making the inducer,burners,and blower MUCH less noticable..of coarse it will cost more than the single speed furnace,,but well worth it if the furnace is on an occupied floor…also i dont think you have to get the evolution series with the complicated tstat to get a 2-speed,ask the salesman….also the warrenties tend to be longer on the higher end equipment,,that could be a reason to consider them even though they cost more…..sorry for writing a book…hope this helps…….dan