Bob,
Me and my dad co-own a HVAC business; however, I'm fairly new to it but have been around these things all my life.
As stated above a 2-Stage furnace can save a lot of money. Say you purchase a 95% 2 Stage 100,000 BTU Furnace
In low heat (1st stage) it may run at 70% which would use 66,500 BTU.
In high heat mode (2nd stage) it will run at 100% which is 95,000 BTU with the other 5,000 BTU going out through the vent.
Of course your furnace will run in 1st stage when it is mild compared to 2nd stage when it's freezing cold.
If you looked at an 80% single stage unit it would be using 100,000 BTU all of the time. Since its only 80% efficient it will lose 20,000 BTU through the vent.
We mainly sell Rheem and American Standard equipment. Rheem is going to be the most expensive, but in my opinion it is by far the best. They are much easier to work on and fix problems.
Just another thing for you to think about is the humidifier. We only have 1 builder that installs humidifiers with the furnace. We have about 5 builders that we do work for. The reason they do not like to install humidifiers because it can potentially rust out your equipment. All of this is based on preference though, there are pro's and con's to both sides.
Are you replacing the coil as well? $3,500 seems a little high for just a furnace change-out, but the equipment may be more expensive in your area.
Let me know if you have any questions and I'll do my best to help you out.
