When should a heat pump with electric backup heat shut off?

A heat pump with electric backup heat is designed to operate efficiently by utilizing the heat pump's primary heating mode until a certain point is reached where it becomes less efficient due to outside temperature conditions. The correct condition for shutting off the heat pump is when the Coefficient of Performance (COP) falls below 1.0.

The COP is a measure of the efficiency of a heat pump; it indicates the ratio of heating provided to the electrical energy consumed. A COP below 1.0 signifies that the heat pump is consuming more energy than it is providing in heat output, which is inefficient and not cost-effective. At this state, it is sensible to switch to backup electric heating to ensure a more consistent and effective heating performance, as the heat pump is no longer capable of effectively meeting the heating demands.

Other thresholds, such as a COP below 3.0, do not represent a point at which the heat pump should be shut off, but rather signifies an acceptable level of efficiency for operation. The choice regarding the electric current draw exceeding 50 amps pertains more to safety and potential overcurrent situations rather than an operational guideline for shutting down the heat pump based on efficiency.

In essence, recognizing when the COP drops below 1.0 is