For example are the 11,200 btu's being used at 40 degrees and the 9,200 at 15 degrees?
The different BTU ratings are determined by the voltage with which the unit is served. The unit can be operated on a 208V circuit that is typical for large commercial buildings in the US, or on a 240V circuit that is typical for residential buildings in the US. The resistance heating element is of a fixed resistance, and when it is energized at a higher voltage, it will draw more current and thus have a higher BTU output.
Date published: 2015-11-16