Heat Pump Winter Care

In heating mode, the heat pump outdoor coil is colder than the outside air. Moisture in the air condenses on the coil and freezes into frost. As frost accumulates, it reduces airflow and efficiency. The heat pump senses this (via temperature sensor or pressure differential) and initiates a defrost cycle. During defrost, the system temporarily reverses to cooling mode—the hot refrigerant from the compressor flows through the outdoor coil, melting the frost. The outdoor fan stops to accelerate heating, and steam rises from the unit. The indoor unit engages auxiliary heat (electric strip heaters) to prevent cold air from blowing into the house. Defrost lasts 5–15 minutes, then the system returns to heating mode. Frequent or prolonged defrost cycles indicate a problem.

Maintain your heat pump for winter efficiency with these steps. Monthly: check and replace or clean the air filter (clogged filters reduce efficiency and can cause defrost problems). Clear snow and ice from around the outdoor unit (maintain 2 feet clearance on all sides). Remove leaves and debris from the outdoor unit cabinet. Check the condensate drain for ice blockage. Seasonal (fall): schedule a professional tune-up—they will check refrigerant charge, clean the coils, inspect the defrost control, and verify auxiliary heat operation. Winter-specific: watch for ice buildup on the outdoor unit between defrost cycles (excessive ice means a problem). Check the auxiliary heat operation by raising the thermostat 5°F above room temperature—you should feel warm air from vents within 5 minutes.

Auxiliary heat (often called electric resistance heat or strip heat) activates when the heat pump cannot keep up with demand—typically when outdoor temperatures drop below the system's balance point. Auxiliary heat is less efficient (1:1 efficiency vs. the heat pump's 2:1 to 4:1) and more expensive to run. Signs that auxiliary heat is running: higher energy bills, the thermostat display shows AUX or EM HEAT, and warm air from vents when the outdoor unit appears to be in defrost. To minimize auxiliary heat use: set the thermostat to a consistent temperature (frequent setbacks force auxiliary heat use during recovery), keep the filter clean, and ensure the outdoor unit is clear of debris and snow. If auxiliary heat runs excessively, the heat pump may need service or the balance point may need adjustment.

Cold-climate heat pumps (sometimes called hyper-heat or low-ambient models) use advanced compressor technology—typically inverter-driven scroll compressors with vapor injection. They deliver full heating capacity at temperatures as low as -10°F to -15°F. Key features: variable-speed compressors adjust output to match demand, enhanced coil designs extract heat from very cold air, and sophisticated defrost controls minimize defrost frequency. These units carry HSPF (Heating Seasonal Performance Factor) ratings of 10+ and COP (Coefficient of Performance) of 2.0+ at 5°F. They cost 15–25% more than standard heat pumps but eliminate or reduce the need for auxiliary heat in cold climates. If you live in an area with winter temperatures below 20°F, a cold-climate heat pump is a worthwhile investment.

A dual-fuel system pairs a heat pump with a gas or propane furnace. The heat pump handles heating in moderate weather (above 35–40°F), and the furnace takes over in cold weather. The system automatically switches fuel sources based on outdoor temperature and energy costs. Benefits: the heat pump provides efficient cooling in summer, the furnace provides fast, reliable heat in winter, and the system optimizes between the two for lowest operating cost. Installation requires both outdoor heat pump and indoor furnace with a control that manages the changeover. Dual-fuel systems cost more than either a heat pump or furnace alone but offer the lowest overall operating cost and best comfort across all climates. Many utility companies offer rebates for dual-fuel installations.