Do Air Source Heat Pumps Work in Winter? A Comprehensive Guide

Air source heat pumps (ASHPs) can indeed work effectively in winter, even in cold climates, but their performance may vary depending on the specific model and outdoor temperature. Modern cold-climate air source heat pumps are designed with features such as variable-speed, inverter-driven compressor technology and improved defrost-cycle controls, allowing them to operate efficiently in temperatures as low as -15°F (-26°C).

Understanding Heat Pump Efficiency in Cold Climates

When the outdoor temperature drops, the heat pump’s efficiency may decrease. However, it’s essential to understand that heat pumps don’t create heat; they move heat from one place to another. Even at low temperatures, there is still some heat available in the outdoor air, albeit in smaller quantities.

The coefficient of performance (COP) is a measure of a heat pump’s efficiency, defined as the ratio of heat moved to the work or electricity cost. A COP of 2, for example, means that the heat pump moves twice as much heat energy as the electrical energy it consumes.

Factors Affecting Heat Pump Efficiency in Winter

  1. Outdoor Temperature: As the outdoor temperature drops, the heat pump’s efficiency decreases. This is because the temperature difference between the indoor and outdoor air becomes larger, requiring the heat pump to work harder to extract heat from the colder outdoor air.

  2. Humidity: Dry, cold air is less efficient for heat pumps to extract heat from compared to moist, warmer air. High humidity levels can help improve the heat pump’s performance in cold weather.

  3. Wind Speed: Strong winds can reduce the heat pump’s ability to extract heat from the outdoor air, leading to a decrease in efficiency.

  4. Defrost Cycles: Heat pumps need to periodically go through a defrost cycle to remove any ice buildup on the outdoor coil. This defrost cycle can temporarily reduce the heat pump’s output and efficiency.

  5. Compressor Technology: Newer, variable-speed, inverter-driven compressors are more efficient at low temperatures compared to older, fixed-speed compressors.

Supplementary Heat Sources for Cold Climates

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In terms of supplementary heat, most homes in cold climates do require some form of backup heat source, especially during extremely low temperatures. This backup heat source can be an existing furnace or a separate heating system. Installing a heat pump with an electric heat strip is another option for maintaining comfort on very cold days.

Types of Backup Heat Sources

  1. Furnace: An existing furnace, whether gas, oil, or electric, can be used as a backup heat source for the heat pump during extremely cold weather.

  2. Auxiliary Electric Heaters: Many heat pumps come equipped with electric resistance heaters, also known as heat strips, that can provide supplementary heat when the heat pump’s efficiency drops.

  3. Dual-Fuel Systems: A dual-fuel system combines a heat pump with a gas or propane furnace, allowing the system to automatically switch between the two heat sources based on outdoor temperature and efficiency.

  4. Ductless Mini-Split Heat Pumps: Ductless mini-split heat pumps often have built-in backup electric resistance heaters to maintain comfort during cold snaps.

Choosing the Right Heat Pump for Cold Climates

When considering a heat pump for a cold climate, it’s crucial to choose a model specifically designed for cold weather. Look for systems that are Northeast Energy Efficiency Partnerships (NEEP) qualified, as these products have been tested and proven to work efficiently in extreme cold.

Features to Look for in Cold-Climate Heat Pumps

  1. Variable-Speed, Inverter-Driven Compressors: These compressors can adjust their speed to match the heating demand, improving efficiency at low temperatures.

  2. Improved Defrost Cycles: Advanced defrost controls can minimize the frequency and duration of defrost cycles, maintaining more consistent heating output.

  3. Low-Temperature Operation: Look for heat pumps rated to operate efficiently in temperatures as low as -15°F (-26°C) or even lower.

  4. High-Efficiency Coils: Specially designed coils can improve heat transfer and maintain performance in cold weather.

  5. Supplementary Heat Options: Consider a heat pump with built-in electric resistance heaters or the ability to integrate with a backup furnace.

  6. Proper Sizing: Ensure the heat pump is sized correctly for your home’s heating load, as an oversized unit may short-cycle and reduce efficiency.

Maintaining and Troubleshooting Cold-Climate Heat Pumps

Proper maintenance and troubleshooting are crucial for ensuring your cold-climate heat pump operates at its best throughout the winter months.

Maintenance Tips

  1. Regular Cleaning: Keep the outdoor unit free of debris, snow, and ice buildup to maintain airflow and heat transfer.
  2. Refrigerant Checks: Ensure the refrigerant charge is correct, as low refrigerant can reduce efficiency and cause icing issues.
  3. Filter Changes: Replace air filters regularly to maintain airflow and system performance.
  4. Thermostat Calibration: Ensure the thermostat is accurately measuring and controlling the indoor temperature.

Troubleshooting Common Issues

  1. Icing on the Outdoor Coil: This can be caused by low refrigerant, airflow issues, or problems with the defrost cycle. Consult a professional for diagnosis and repair.
  2. Reduced Heating Capacity: If the heat pump is not providing enough heat, check for airflow obstructions, refrigerant issues, or problems with the backup heating system.
  3. Short-Cycling: If the heat pump is turning on and off frequently, it may be oversized for the home’s heating load or have a problem with the compressor or controls.
  4. Unusual Noises: Strange sounds from the heat pump may indicate a mechanical issue, such as a failing compressor or fan motor.

In summary, air source heat pumps can work effectively in winter, even in cold climates, but their performance may vary depending on the specific model and outdoor temperature. By choosing a cold-climate rated heat pump, understanding the factors that affect efficiency, and properly maintaining the system, you can ensure your heat pump provides reliable and efficient heating throughout the winter months.