@sickburnbro @hazlin @BowsacNoodle @jeffcliff @skylar True, but there are only two inputs to the system: temperature from the air or ground that is pumped into the controlled space and electricity to run the compressor and other components of the system, and one output (heat in the cooled/heated space). If you measure those accurately, you can treat the complex heat pump system as a black box with equivalent input/output and safely ignore the internals.