Efficiency multiplier at moderate temperatures
Heat pumps excel at turning electricity into useful heat, delivering 3-4 units of energy for every unit of electricity consumed when outdoor air sits around 45-55 degrees Fahrenheit. This efficiency multiplier, called the coefficient of performance (COP), arises because the system transports existing heat rather than generating it from scratch like resistance heating does. At these comfortable operating points, the compressor works lightly and the system achieves its design sweet spot. The result is a dramatic advantage over electric resistance baseboard heating, which burns energy at a 1-to-1 ratio.
Why cold weather erodes performance
As outdoor temperature drops below freezing, the refrigerant cycle must work harder to extract heat from progressively colder air, and the compressor consumes more electricity to maintain pressure differentials. COP falls sharply, sometimes hitting 1.5 or lower in extreme cold, meaning the system becomes little better than electric resistance baseboard heat. Many climates with regular sub-zero weather pair heat pumps with a backup resistive element to maintain capacity and efficiency thresholds. This two-stage approach preserves the COP advantage during the mild and moderate seasons while ensuring comfort and reliability during the coldest weeks.