Staying Warm in Hamilton: Do Heat Pumps Lose Efficiency Below –15°C?

 When the "Polar Vortex" hits the Greater Hamilton Area and the temperature drops past –15°C, homeowners across the city—from the Mountain to the Bayfront—start to worry. If you’ve made the switch to a modern heat pump, you might have heard the lingering myth: "Heat pumps don't work in real Canadian winters."

As the local experts at Dynamic Heating and Cooling, we’re here to set the record straight for 2026. While it’s true that heat pumps face challenges in extreme cold, the technology has evolved significantly. In this guide, we’ll dive deep into the science of sub-zero efficiency, the "economic balance point" for Hamilton utility rates, and how to ensure your home stays comfortable even when the lake begins to freeze.

1. The Science of the "Efficiency Cliff": Reality vs. Myth

Many homeowners believe that –15°C is a "magic number" where a heat pump simply stops producing heat. This is a misunderstanding of how thermodynamics works.

A heat pump’s efficiency is measured by its Coefficient of Performance (COP). A COP of 1.0 is the baseline for electric resistance heating (like a space heater). Modern heat pump replacement units, specifically those rated as "Cold Climate Air Source Heat Pumps" (ccASHPs), are designed to operate at much higher efficiencies.

Even at –15°C, a high-quality unit will typically maintain a COP of 2.0 to 2.5. This means for every 1 unit of electricity used, you are still getting 2 to 2.5 units of heat. In comparison, a gas furnace is usually around 0.95 (95%) efficient. While the efficiency decreases as it gets colder, the heat pump remains technically more efficient than almost any other heating source.

2. The 2026 "Economic Balance Point" in Hamilton, ON

While a heat pump is scientifically efficient at –15°C, the real question is: Is it cheaper to run than a furnace? This is known as the Economic Balance Point.

In Hamilton, we have to consider the current 2026 electricity rates from Alectra Utilities versus natural gas prices. Because electricity is generally more expensive per unit of energy than gas in Ontario, there is a specific temperature where it becomes more cost-effective to switch to your backup gas furnace.

For most Hamilton homes, this point is usually between –10°C and –12°C. If you have a hybrid system installed by a professional HVAC replacement service, your thermostat can be programmed to automatically switch to gas when it hits this threshold, ensuring you always pay the lowest possible bill.

3. Understanding Capacity vs. Efficiency

There is a crucial distinction between efficiency (how much heat you get per dollar) and capacity (how much total heat the machine can pump out).

As it gets colder, the air becomes less dense. This means the outdoor unit has to move more air and work the compressor harder to extract the same amount of thermal energy. At –15°C, a unit might only be able to provide 60-80% of its rated capacity.

This is why proper sizing is vital. If your unit is too small, it won't be able to keep up with the heat loss of your home in January. This is where heat pump repair and maintenance experts can help you determine if your system is underperforming or if it was simply undersized for the local climate.

4. The Role of "Auxiliary Heat" and When to Use It

If you’ve seen the "AUX" light on your thermostat during a cold snap, don't panic. This signifies that your HVAC maintenance system has triggered its backup heat source—usually electric heat strips or a gas furnace—to supplement the heat pump.

·        Electric Backup: Uses more energy and is more expensive. It’s meant for short bursts.

·        Gas Backup (Dual Fuel): This is the most popular setup in Hamilton. It allows the heat pump to do the "heavy lifting" during the spring and fall, while the furnace takes over during the deep winter months.

If your AUX heat is running constantly when it’s only –5°C, you likely need a heat pump tune-up to ensure the outdoor coils are clean and the refrigerant levels are correct.

5. Managing the Defrost Cycle in Humid Hamilton Winters

Hamilton’s proximity to the water means our winters are often humid. This humidity causes frost to build up on the outdoor coils of your heat pump.

To clear this, the system enters a Defrost Cycle. It temporarily reverses the flow of refrigerant to warm the outdoor coils and melt the ice. You might see steam rising from the unit or hear a "whooshing" sound. This is perfectly normal! However, if the ice doesn't melt and your unit looks like a solid block of ice, you should call for heat pump repair immediately, as a blocked coil can burn out the compressor.

6. 2026 Refrigerant Changes: The Move to R-290 and R-454B

2026 marks a major shift in the HVAC industry as older R-410A refrigerants are phased out for more eco-friendly options like R-290 (Propane) and R-454B.

For Hamilton homeowners, this is actually good news for cold-weather performance. R-290, in particular, has excellent thermodynamic properties that allow heat pumps to maintain higher output temperatures even when the mercury drops to –20°C. If you are considering renting an HVAC system, ask about these newer, high-performance models.

7. Why Professional Maintenance is Non-Negotiable

A heat pump is a sophisticated piece of machinery. Unlike a furnace, it runs year-round—cooling in the summer and heating in the winter. This double duty means that regular maintenance is essential to maintain efficiency.

At Dynamic Heating and Cooling, we recommend joining our Dynamic Member Club to ensure your system is inspected before the heating season begins. A technician will check:

·        Refrigerant charge (crucial for low-temp performance).

·        Fan motor and compressor health.

·        Sensor calibration (to ensure the defrost cycle triggers correctly).

·        Drainage (to prevent ice build-up at the base of the unit).

Actionable Tips for Hamilton Homeowners

1.     Don't Use "Emergency Heat" Manual Mode: Unless your heat pump is physically broken, let the thermostat manage the transition. "Emergency Heat" locks out the heat pump and uses the most expensive fuel source.

2.     Clear the Snow: After a Hamilton snowstorm, ensure there is at least 2 feet of clear space around your outdoor unit. A buried unit cannot move air and will lose efficiency instantly.

3.     Upgrade Your Insulation: A heat pump works best in a well-sealed home. If your attic insulation is lacking, your heat pump will struggle to maintain –15°C regardless of its efficiency.

4.     Set it and Forget it: Avoid large temperature "setbacks" at night. Heat pumps are most efficient when maintaining a steady temperature rather than trying to "catch up" by 5 degrees in the morning.

Summary: The 2026 Verdict

Do heat pumps lose efficiency below –15°C? Yes, but they are still incredibly effective. In Hamilton’s climate, the key is not just the heat pump itself, but a properly designed hybrid system. By combining a high-efficiency heat pump with a reliable gas backup, you maximize your savings, minimize your carbon footprint, and guarantee comfort no matter what the Ontario winter throws your way.

Ready for a warmer winter? Contact Dynamic Heating and Cooling today for a professional inspection or to discuss a new cold-climate installation. Call us at 289-204-3358 or visit our contact page to book your appointment.