The human body cannot be reduced to be equivalent to a fireplace. That oversimplification just shows ignorance of the complexity involved. FUnny coincidence, I ran into this todayIrrelevant since the person can't micromanage all of that. There are no special snowflakes when it comes to energy turnover.
The person is either eating too many calories or their body is a self sustaining energy source. Occam's razor would point to the former.