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Emergency Heat Strips and Why HVAC Contractors Incorrectly Disable Them

Heat pumps have an emergency/auxiliary (AUX) back up heat system that is designed to provide heat in case of heat pump failure (AUX also heats during unit defrost and when the heat pump can’t meet demand due to cold outdoor temperatures).

After 2012 (when Energy Code was adopted), some HAVC contractors program systems such that AUX heat will not turn on when thermostat is set in AUX heat mode if the outdoor temperature is above 40 degrees.


This is incorrect. AUX heat should ALWAYS turn on when the thermostat is set to AUX mode, regardless of outdoor temperature.


Let’s say you have a heat pump failure (capacitor, transformer, compressor, etc). To obtain heat, you would simply switch the thermostat to AUX heat, raise the temperature, and heat should be generated. With some contractors, they lock out your AUX heat if above 40 degrees outside. You would be quite cold in your home without heat! And, for how long? Parts shortages, etc. You could be without a source of heat for weeks.


The confusion is that, per Energy Code requirements, AUX heat should not turn on when the heat pump compressor can meet the heating demand if above 40 degrees outside. When the thermostat is set in AUX mode, the heat pump compressor will not operate, thus the compressor is not relevant to the requirement.

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