Heat pumps typically do not completely stop working, even when outdoor temperatures drop significantly. Instead, their efficiency decreases, and they increasingly rely on supplementary heating systems to maintain desired indoor temperatures.
Understanding Heat Pump Performance in Cold Weather
While some heat pumps begin to lose efficiency when outdoor temperatures dip below 32°F (0°C), they are designed to continue operating. The system's ability to maintain warmth depends on several factors, including the specific model, its design, and your thermostat settings. If you want to keep your home warm during sub-zero temperatures, you will likely notice a decrease in the heat pump's performance capabilities.
How Heat Pumps Operate in Cold
Heat pumps work by extracting heat from the outdoor air and transferring it indoors. As outdoor temperatures fall, there is less heat available to extract, making the process more energy-intensive. This leads to a drop in the system's Coefficient of Performance (CoP), which is a measure of its efficiency.
Most modern heat pumps are equipped with auxiliary heat (also known as supplemental or backup heat), often in the form of electric resistance coils, or they are paired with a gas furnace in a dual-fuel system. When the outdoor temperature drops below a certain point (known as the "balance point," usually between 20°F and 40°F, or -6.7°C and 4.4°C), the heat pump may not be able to meet the heating demand alone. At this point, the auxiliary heat kicks in to assist or take over completely, ensuring your home remains comfortable.
Factors Affecting Cold-Weather Performance
Several factors influence how well a heat pump performs in cold conditions:
- Heat Pump Type:
- Air-Source Heat Pumps: These are the most common and draw heat from the air. Their efficiency is most affected by dropping air temperatures.
- Geothermal Heat Pumps: These extract heat from the stable underground temperature, making them largely unaffected by fluctuating air temperatures and highly efficient even in extreme cold.
- Cold-Climate Heat Pumps: Newer generations of air-source heat pumps are specifically designed to operate efficiently at much lower temperatures, some even down to -15°F (-26°C) or lower, before significantly relying on auxiliary heat.
- System Sizing and Installation: A properly sized and professionally installed heat pump will perform better in colder conditions.
- Maintenance: Regular maintenance ensures the system runs at peak efficiency.
- Insulation and Home Sealing: A well-insulated and air-sealed home retains heat more effectively, reducing the burden on the heat pump in cold weather.
- Thermostat Settings: If you set your thermostat very high during extremely cold weather, the heat pump will have to work harder, potentially losing performance and relying more on auxiliary heat.
Performance Summary by Temperature
The following table illustrates general heat pump performance across various outdoor temperature ranges:
| Outdoor Temperature Range | Heat Pump Performance Characteristics |
|---|---|
| Above 40°F (4.4°C) | Optimal Performance: Heat pump operates efficiently as the primary heating source. |
| 32°F (0°C) - 40°F (4.4°C) | Efficiency Begins to Decrease: Performance may start to decline; supplemental heat might engage intermittently. |
| 15°F (-9.4°C) - 31°F (-0.6°C) | Increased Reliance on Auxiliary Heat: Heat pump still provides heat but relies more on backup; efficiency is noticeably lower. |
| Below 15°F (-9.4°C) | Significant Performance Drop: Heat pump contributes less heat; auxiliary heat or dual-fuel furnace becomes the primary heating method. |
| Sub-Zero Temperatures | Limited Contribution: Heat pump runs, but provides minimal heat; system heavily relies on auxiliary heat. |
In summary, while a heat pump won't completely stop working, its ability to efficiently heat your home as the sole source diminishes significantly in very low or sub-zero temperatures, at which point its built-in auxiliary heating system or a paired furnace will take over to maintain comfort.
