Traditional air-source heat pumps can provide reliable heating when outdoor temperatures are moderately cold. However, once the weather reaches subzero temperatures, heat pumps suffer a drastic loss of performance due to frost accumulation on their outdoor units.
Cold climate heat pumps have design features that reduce the need for frequent defrosting. These include built-in heaters for their outdoor units, which prevent ice and snow accumulation. Even if outdoor temperatures have dropped below 0°C (32°F), cold climate heat pumps can operate continuously. Some HVAC manufacturers now offer heat pumps capable of operating at temperatures as low as -26°C (-15°F).