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