Thanks all for the informative discussion. Quickcat, that was also my confusion since the AS literature says "operates quietly and efficiently with its multispeed blower motor" but it is called "Freedon 80 High Efficiency Single-Stage Furnace". My contractor said the blower motor is multispeed since he will set its speed for 1600 cfm for the 4ton A/C when the system is installed, but it blows at a constant speed.
I was disappointed in this since I have heard good things about multi-speed (2-stage) furnaces (comfort and saving $$). But it looks like the for AS 2-stage furnaces the stages are usually 65% and 100% x BTUs so it is only a 35% stepdown anyway rather than the 50% I had thought. I did ask if it could be modded afterwards (thermostat or circuit board easy?) for 2-stage operation but his answer was no.
I do not know if the AS system is less efficient with 2-stage/VS blowers or if AS just did not test and qualify it for the Fed Tax Credit.
To be installed (AHRI 3438368): Allegiance 15 4A7A5048E1/4TXFH004BS3HHA/AUD1C080A9H41B.
I am being supplied the ACONT800 thermostat but I did ask for the HW VisionPRO IAQ as mentioned on this site. I was told the 800 was the same as the IAQ except the IAQ has some features that this system would not use and that AS requires an AS thermostat to get the 10/10/10 warranty anyways.
Another question I have: My old furnace was a 100,000 BTU Consolidated (~65% eff?) so with the new 80,000 BTU furnace (80% eff) I should have the same amount of heat in the house since 100k x 0.65 ~ 80k x 0.80. Is this correct? The old furnace was just fine for heat.