For this furnace efficiency exercise, annual useful heat output is 81 million Btu and annual fuel input is 90 million Btu. Using output divided by input, what is the annual efficiency?
- A9%
- 90%
- C81%
- D111%
Where to look it up
Explicit exercise assumptions; not a universal code requirement.
Why B is correct
81 / 90 × 100 = 90%. This compares annual energy quantities; it does not assert a minimum AFUE for every public building.