The extra energy you use mostly ends up as thermal energy, but some may end up as sound or chemical changes in the staircase, etc.
(The extra energy; use; you) (The extra energy you use; mostly ends up; as thermal energy) (some; may end up; as sound or chemical changes in the staircase, etc.)
The extra energy The extra energy you use some
use mostly ends up may end up
you
as thermal energy
as sound or chemical changes in the staircase, etc.