Why is my heat pump not keeping up when it drops below minus 20?
Why is my heat pump not keeping up when it drops below minus 20?
Most heat pumps lose significant heating capacity at extreme cold temperatures, and -20°C is right at the threshold where many standard units start struggling. This is a common issue across New Brunswick, especially during those brutal January and February cold snaps that regularly hit -25°C to -35°C in areas like Fredericton, Woodstock, and northern communities.
Heat Pump Performance Drop-Off
The physics of heat pump operation means they extract less heat from outdoor air as temperatures plummet. A typical heat pump that delivers 100% of its rated capacity at 8°C might only produce 60-70% capacity at -20°C, and some older or standard-efficiency units drop even further. When your home's heat loss increases dramatically in extreme cold (due to greater temperature differential), but your heat pump's output is decreasing, you get that uncomfortable gap.
Cold Climate vs Standard Units
If your heat pump isn't specifically rated as "cold climate" or doesn't have a heating capacity rating down to -25°C or -30°C, it's likely not designed for New Brunswick's winter extremes. Many heat pumps installed in the province over the past decade were sized for milder climates and struggle with our harsh winters. Cold-climate heat pumps use enhanced vapor injection, variable-speed compressors, and specialized refrigerants to maintain capacity at low temperatures.
Backup Heating Systems
Most New Brunswick heat pump installations should include backup heating for exactly this scenario. This might be electric baseboard heaters, your existing oil furnace (if you converted from oil), or electric resistance coils built into the heat pump's air handler. When outdoor temperatures drop below your heat pump's effective range, the backup system should automatically kick in. If you don't have backup heat or it's not working properly, that explains why you're getting cold.
Sizing and Installation Issues
Heat pumps need to be properly sized for both your home's heat loss and New Brunswick's climate. An undersized unit will struggle even in moderate cold. Additionally, outdoor units need adequate airflow and should be elevated above expected snow levels - something particularly important given our 250-350cm annual snowfall. If the outdoor unit is blocked by snow or ice buildup on the coils, performance drops significantly.
What You Can Do Right Now
Check that your outdoor unit isn't blocked by snow or ice, and ensure your backup heating system is functioning. If you have electric baseboard heaters or an oil furnace as backup, make sure they're operational. Contact a licensed HVAC contractor through our New Brunswick directory to assess whether your system is properly sized and configured for our climate - you may need a cold-climate upgrade or additional backup capacity to handle those -20°C and below nights that are simply part of winter life in New Brunswick.
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