Modern heat pumps have become a key component of residential heating in Québec, especially for homeowners seeking to reduce energy consumption without sacrificing winter comfort. Yet one question often comes up: how can a system extract heat from air that feels icy cold, sometimes at –10 °C or –20 °C? This guide explores in depth the physical mechanisms that make this possible, along with the factors that influence performance, proper sizing, and maintenance best practices. It is intended for both homeowners and professionals looking to deepen their understanding of high-efficiency heating systems.
1. How a heat pump captures outdoor heat in the middle of winter
A heat pump operates on a well-known principle in thermodynamics: the reversed refrigeration cycle. This cycle relies on the ability of a refrigerant to evaporate at extremely low temperatures, absorbing available heat from outdoor air even in very cold conditions.
1.1 Understanding the reversed refrigeration cycle
The cycle begins when the refrigerant, at very low pressure, evaporates inside the outdoor evaporator. This evaporator absorbs heat from the cold air. Even at –10 °C, air still contains thermal energy, enough to allow the refrigerant to evaporate. Once vaporized, the refrigerant is compressed by the compressor, which raises both its pressure and temperature. This heat is then transferred indoors through the condenser.
This cycle repeats continuously, creating efficient heat transfer and allowing the heat pump to provide steady heating throughout the winter season.
1.2 Low-temperature performance: a measurable reality
Studies conducted on air-source systems show varying performance depending on model and operating conditions. At –8 °C, observed coefficients of performance (COP) often range between 1.1 and 3.7. This level of efficiency already exceeds that of standard electric resistance heating. At milder temperatures, such as +8 °C, some models reach a COP of 5.4, demonstrating an exceptional ability to multiply delivered energy.
These variations are explained by the density of heat available in the air and by the technology used, particularly variable-speed compressors.
2. Performance comparison based on outdoor temperature
To better understand the relationship between outdoor temperature and heat pump efficiency, it is useful to compare different system types.
2.1 Performance comparison by system type
The following table illustrates how COP varies depending on temperature and technology.
Table 1 – Performance comparison by temperature
| Heat pump type | Outdoor temperature | Coefficient of performance (COP) |
| Standard air-source | +8 °C | 2.0 to 5.4 |
| Cold-climate air-source | –8 °C | 1.1 to 3.7 |
| Geothermal | Independent | 3.5 to 5.0 |
Geothermal systems offer more stable efficiency because their energy source is the ground, where temperatures remain relatively constant throughout winter. In contrast, air-source systems are more affected by weather variations, though cold-climate models still deliver strong performance.
2.2 How to maintain winter performance
Performance also depends on coil cleanliness, defrost efficiency, and stable airflow. Experts recommend keeping the outdoor unit clean and unobstructed to allow free air circulation.
It has been observed that proper maintenance, including coil cleaning and verification of automatic defrost operation, can improve heat pump efficiency by up to 10%. These actions reduce compressor workload and enhance heat delivery.
3. Proper sizing and energy savings
Accurate sizing is essential to ensure heat pump performance. An oversized system will cause frequent start-stop cycles, reducing overall efficiency. Conversely, an undersized unit may struggle to meet heating demand during extreme cold.
3.1 Sizing criteria based on recognized standards
In practice, professionals rely on the CSA-F280-12 standard to determine required heating and cooling capacity. This standard considers factors such as:
- living area size;
- building insulation level;
- wind exposure;
- internal heat gains;
- regional climate conditions.
An analysis based on these criteria helps select a system whose COP remains optimal under real operating conditions.
3.2 Comparison of key sizing factors
Before reviewing the summary table, it is important to remember that these factors interact. A well-insulated home requires less capacity than one that is more exposed.
Table 2 – Comparison of sizing factors
| Factor | Impact on performance | Evaluation method |
| Outdoor climate | Affects COP and heating demand | Regional temperature data |
| Building insulation | Reduces heating demand | Wall, window, and attic analysis |
| System type | Influences COP stability | Air-source vs. geothermal |
Combining these elements structures the selection of the appropriate capacity and model. Proper sizing ensures meaningful energy savings and stable winter performance.
4. Preventive maintenance and system lifespan
A properly maintained heat pump can deliver years of stable performance. Regular maintenance reduces breakdown risks and improves energy efficiency.
4.1 Essential preventive maintenance tasks
Before listing tasks, it is important to note that maintenance aims to ensure optimal airflow and refrigerant levels in line with manufacturer recommendations.
Recommended tasks include:
- cleaning air filters every three months;
- visually inspecting the outdoor coil for dust or excessive frost;
- annual refrigerant level checks by a qualified technician;
- monitoring the compressor and electrical components.
These simple actions help extend system lifespan and maintain consistent performance.
4.2 Typical lifespan and general guidelines
Air-source heat pumps typically last between 15 and 20 years, while geothermal systems can reach up to 25 years. Longevity depends on maintenance, climate conditions, and daily use.
Careful adherence to technical recommendations helps prevent performance losses caused by frost, restricted airflow, or internal component degradation.
5. Frequently asked questions about winter heat pump use
Users often question the real heating capacity of heat pumps in winter and the best maintenance practices.
5.1 FAQ – Cold-weather operation
Does a heat pump still heat at –20 °C?
Yes. Recent cold-climate models generally maintain acceptable performance down to around –20 °C.
What is the average lifespan of a heat pump?
Between 15 and 20 years for air-source heat pumps, and up to 25 years for well-maintained geothermal systems.
How can I tell if my heat pump is properly sized?
A load calculation compliant with the CSA-F280-12 standard can confirm whether system capacity matches your home’s needs.
Conclusion
A heat pump extracts outdoor heat using proven thermodynamic mechanisms, allowing indoor comfort even in subzero temperatures. Performance depends on installation quality, accurate sizing, and regular maintenance. Homeowners seeking to optimize their system can benefit from a professional evaluation to adjust capacity, improve efficiency, and maximize equipment lifespan. For tailored analysis or specialized support, Réfrigération Jolicoeur offers evaluation and advisory services designed to maximize winter heat pump efficiency.