Heat Pump Not Heating in Cold Weather? Here's Why
Heat pumps can struggle in cold weather. Learn what is normal, what indicates a problem, and when to call for service.
Heat pumps are efficient heating systems, but they work differently than traditional furnaces. Understanding how they operate helps you know when there is a real problem versus normal behavior.
How Heat Pumps Work
Heat pumps extract heat from outdoor air and transfer it inside. Yes, even cold air contains heat that can be extracted—though efficiency decreases as temperatures drop.
Normal Cold Weather Behavior - **Longer run times:** Heat pumps may run almost continuously in cold weather. This is normal. - **Cooler supply air:** Air from vents will feel cooler than from a gas furnace but should still be warm (85-95 degrees typically) - **Defrost cycles:** The outdoor unit will periodically defrost, which may look like steam or smoke (condensation) - **Auxiliary heat activation:** Electric backup heat may run during very cold periods or defrost
Signs of Actual Problems
Ice Buildup That Does Not Clear Some frost on the outdoor unit is normal. Persistent ice that does not clear during defrost cycles indicates a problem: - Defrost cycle failure - Low refrigerant - Fan problems - Control issues
No Warm Air at All If air from vents is not warm: - Check thermostat is set to heat mode - Verify outdoor unit is running - Check for ice on outdoor unit - Ensure emergency heat is not accidentally selected
Auxiliary Heat Running Constantly If the "Aux Heat" or "Emergency Heat" indicator stays on continuously when outdoor temperatures are above freezing, the heat pump may not be working properly.
Unusual Sounds - Grinding or scraping - Loud buzzing - Clicking without starting - Hissing sounds
What You Can Check
Thermostat Settings - Set to "Heat" not "Emergency Heat" - Temperature set appropriately - Fan on "Auto"
Air Filter - Replace if dirty - Restricted airflow reduces efficiency
Outdoor Unit - Clear snow, ice, and debris - Check that fan is spinning - Ensure airflow is not blocked
Circuit Breakers - Check both indoor and outdoor breakers
When to Call for Service
- Outdoor unit is iced over and not defrosting
- No warm air despite proper settings
- Auxiliary heat running when temperatures are moderate
- Strange sounds or smells
- System short cycling
- Refrigerant leak signs (hissing, ice on lines)
Bay Area Heat Pump Notes
The Bay Area's mild climate is actually ideal for heat pumps. Temperatures rarely drop below efficient operating range, making heat pumps a smart choice here. If your heat pump struggles in our relatively mild winters, something may be wrong with the system.