Interpreting Hot Air Furnace Specs Quest. ?

Hello:
Want to verify that my understanding of the following is correct, please:
In the Trane/American Std hot air furnace brochures, they have model designations as: TUD 100 R9V3K
The 100 is apparently the heat size for the unit (it is not labeled with BTU, or anything else, though)
a. This would be for the heat INPUT, right ?
Then, there's a Stage 1 and a Stage 2 BTUH number. This is obviously the heat OUTPUT as 80% of the 100 number gives the listed stage 2 BTUH number, so it seems to make sense ?.
b. Is it true that the furnace only utilizes stage 1, OR stage 2, and Never both together ?
c. BTW: shouldn't it be in BTU/H rather than BTUH ?
Thanks, Bob
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a. Yes
b. It does not really matter for on low speed it puts out Z amount of heat and On high speed it put out 2 X Z amount of heat. We would have to get complex to just start to explain this.
c. Yes -- BTU Per Hour.
You also need to read the installation instruction and get a bunch of your questions answered here.
TURTLE
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