This is one of the most common questions homeowners ask when considering a heat pump—especially in colder regions: at what outside temperature do heat pumps stop working?
The short answer is: most modern heat pumps do not suddenly stop working at a specific temperature, but their heating capacity and efficiency gradually decrease as outdoor temperatures drop.
Today, many cold-climate heat pumps are specifically designed to continue operating—and providing usable heat—well below freezing.
Do Heat Pumps Really Stop Working in Cold Weather?
In practical terms, a heat pump can stop running for very different reasons.
1. Performance Limitation (Most Common)
In most real-world situations, a heat pump is still mechanically capable of running, but it can no longer produce enough heat to meet the home’s heating demand efficiently. This is what many homeowners mean when they say a heat pump has “stopped working.”
2. Low-Temperature Operational Cutoff (Actual Shutdown)
Heat pumps are designed with a minimum operating temperature. If outdoor temperatures drop below this threshold, the system may automatically shut down to protect internal components such as the compressor and refrigerant circuit.
This cutoff temperature varies by model and manufacturer. For many cold-climate mini split systems, this minimum operating limit is around -13°F, while certain ultra-low-temperature models—such as the TOSOT Aoraki Series—are engineered with protection logic that allows operation down to approximately -22°F. For extreme cold areas,
A heat pump may still be rated to operate at a given temperature, but that does not mean it can deliver full—or even sufficient—heating capacity at that point.
3. Defrost Function in Cold and Humid Conditions
In cold, humid environments, frost can form on a heat pump’s outdoor coil, reducing heating efficiency. Modern heat pumps use automatic defrost systems to manage this. During defrost cycles, the heat pump may temporarily stop heating or blow cooler air. Many users mistake this for a malfunction and may turn off the system, which can worsen frost buildup. In reality, automatic defrosting is a normal process and requires no manual intervention.
4. Other Conditions That Can Cause a Heat Pump to Stop Running
In addition to low outdoor temperatures, an outdoor unit may also stop operating due to other issues, including:
- Power outages or electrical supply interruptions
- Control board or sensor faults
- Refrigerant-related issues (such as pressure protection triggers)
- Excessive ice buildup or blocked airflow
- Defrost system malfunctions
These situations are not directly related to outdoor temperature limits but can still result in a temporary or complete system shutdown.
Please note that a heat pump may still be rated to operate at a given temperature, but that does not mean it can deliver full—or even sufficient—heating capacity at that point.
Why Heat Pump Performance Drops as Temperature Falls
Heat pumps move heat rather than generate it. As outdoor air gets colder, there is less available heat energy to extract. This is why experienced installers recommend looking beyond peak efficiency ratings. Instead, homeowners should review heating capacity and COP at multiple outdoor temperatures, such as 47°F, 17°F, and 5°F. These data points provide a far more realistic picture of cold-weather performance.
When Does a Backup Heat Source Become Necessary?
In regions that experience prolonged or extreme cold—such as parts of the northern United States—having a backup heat source is strongly recommended.
One common approach is a dual-fuel (hybrid) system, where a central heat pump is paired with a gas furnace. In this setup, the heat pump operates during mild to moderately cold weather, and once outdoor temperatures fall below a preset lockout point, the system automatically switches to the furnace.
In addition to gas furnaces, backup heat can also take other forms. Electric resistance heat (such as built-in auxiliary heaters or electric baseboards) is frequently used as a secondary or emergency heat source, particularly in all-electric homes. These systems are not as energy-efficient, but they provide reliable and predictable heat output during extreme cold.
For extreme cold climates, a hybrid approach—combining a heat pump with electric resistance heat or a gas furnace—offers the best balance of efficiency, reliability, and peace of mind.
Tips for Using Mini Split Heat Pumps in Cold Climates
If you rely on a mini split heat pump as your main heating source, the following best practices—commonly discussed among installers and experienced DIY homeowners—can help improve performance in winter.
1. Improve Home Insulation
A well-insulated home dramatically reduces heat loss. Air sealing, window upgrades, and proper attic insulation can make the difference between a heat pump struggling and performing reliably in cold weather.
2. Keep the Outdoor Unit Clear—but Not Enclosed
Do not fully cover or seal the outdoor condenser. Heat pumps require constant airflow to extract heat from outdoor air. Snow and ice should be removed regularly, but airflow must remain unobstructed.
Many homeowners in snowy regions install a small roof or awning above the unit or use breathable covers—solutions frequently recommended in cold-climate HVAC discussions.
3. Maintain a Steady Thermostat Setting
Frequent on-off cycling during cold weather increases preheating time and energy use. Maintaining a consistent indoor temperature helps the system operate more efficiently.
4. Manage Ice Buildup Carefully
Some DIY users spread rock salt (halite) on the ground around the outdoor unit to help melt ice buildup during extreme cold events. Rock salt lowers the freezing point of water, allowing ice to melt and drain more easily.
⚠️ Salt should never be applied directly to the condenser or mechanical components, as it can cause corrosion. This should only be considered a short-term emergency measure.
Recent winter storms and extreme cold events have impacted many regions, disrupting daily life and putting added strain on home heating systems. We hope everyone affected stays safe, warm, and well during these challenging conditions. See you in the warm spring and summer. If you have any ideas to share with us, feel free to drop us an email at support@tosotdirect.com.
