Why Your Heat Pump Runs Constantly In Cold Weather: Causes, Solutions, And Energy Efficiency Tips

When temperatures drop, it’s common for American homeowners to notice their heat pump runs constantly in cold weather. While this behavior can be normal, it may also signal underlying issues or inefficiencies. This detailed guide examines key reasons for continuous operation, how heat pumps work during winter, when to be concerned, and effective strategies for improving comfort and reducing energy costs.

How Heat Pumps Operate In Cold Weather

Heat pumps use refrigeration cycles to extract ambient heat from outdoor air, even in cold conditions, and transfer it inside. As outdoor temperatures fall, the available heat decreases, making the system work harder and often causing it to run for extended periods.

Extracts heat from outside air and delivers it indoors through a refrigerant cycle.
Becomes less efficient below 32°F, often requiring longer run times to meet set temperatures.
Many modern units have auxiliary (electric resistance) heat to provide extra warmth when needed.

Continuous operation in cold weather is not always problematic; in many scenarios, it is designed to provide consistent comfort efficiently.

Is It Normal For A Heat Pump To Run Constantly In Cold Weather?

During cold snaps, especially in northern U.S. and Midwest regions, heat pumps often run nearly nonstop. This helps maintain indoor comfort but can raise questions about whether the system is functioning properly. Consider the following points:

Condition	Normal Behavior?
Outdoor Temp 35°F – 45°F	Moderate cycling, some longer run times
Outdoor Temp 20°F – 34°F	Long run times, minimal shutdown
Outdoor Temp Below 20°F	May run nearly 100% with auxiliary heat engaged

Prolonged running at very low temperatures is typical, but if the system fails to reach the thermostat setpoint or energy bills spike, further assessment may be needed.

Why Heat Pumps Run Longer As Temperatures Drop

Heat pumps are designed to maximize efficiency at moderate temperatures. Below freezing, their heating capacity decreases, and the compressor stays on longer. The main reasons include:

Lower ambient heat means the system must extract heat from increasingly colder air.
Defrost cycles are triggered periodically to remove frost from outdoor coils, further increasing run time.
Auxiliary heat strips may activate when the desired temperature cannot be met by the heat pump alone.

In especially cold weather, the balance point—the temperature at which a heat pump can match the home’s heating needs—may be exceeded. The result is near-continuous operation.

Main Causes Of Excessive Or Unusual Run Time

While constant running is often normal during freezing weather, other factors can contribute to excessive runtimes or poor performance:

Improper Sizing:

If a heat pump is too small for the home, it will struggle to heat effectively in cold weather, running continuously without satisfying the thermostat.
Dirty Air Filters Or Coils:

Dirty filters or outdoor coils impede airflow and heat transfer, forcing the system to work harder and stay on longer.
Low Refrigerant:

Refrigerant leaks or low levels can reduce heating power and trigger more frequent or extended cycles.
Aging Or Inefficient Equipment:

Older models lack advanced cold-weather optimization found in many newer systems, leading to longer operational periods.
Leaky Or Poorly Insulated Home:

Heat loss through gaps, old windows, or inadequate insulation increases the heat load, making even a well-functioning heat pump run continuously.
Malfunctioning Defrost Controls Or Thermostat Issues:

If the defrost mode activates too often or the thermostat malfunctions, the system may run unnecessarily.

Identifying If There’s A Problem With Your Heat Pump

Not all nonstop running is normal. Look for the following warning signs indicating your heat pump may need maintenance or repair:

Unit blows cool air instead of warm when heating mode is active.
Sudden spikes in utility bills not explained by extreme cold alone.
Frequent or rapid cycling between modes, or unusual noises.
The indoor temperature never reaches the setpoint even after hours of operation.
Ice buildup on the outdoor unit that does not clear during defrost cycles.

If any of these issues appear, it is wise to schedule a professional HVAC service call.

Energy Efficiency Of Heat Pumps In Cold Climates

While heat pumps are considered highly efficient in mild and moderate climates, their performance changes as the mercury drops. Efficiency is measured by the Heating Seasonal Performance Factor (HSPF) and the Coefficient of Performance (COP). In cold climates:

Modern cold-climate heat pumps use advanced compressors and refrigerants to maintain higher efficiency in subfreezing weather.
Auxiliary heat usage can reduce system efficiency and raise utility costs, especially during extended cold spells.
Heat pumps remain more efficient than electric resistance heating for most of the year, but in extreme cold (below 15°F) their cost advantage narrows unless they are specifically designed for such temperatures.

Technology	Performance in Moderate Cold (30°F – 40°F)	Performance in Deep Freeze (Below 20°F)
Standard Heat Pump	Efficient, minimal aux heat needed	Efficiency drops, aux heat frequently used
Cold Climate Heat Pump (ccASHP)	Very efficient, retains heating capacity	Maintains better efficiency, reduced aux heat dependency

Efficiency drops are normal, but technology advancements are minimizing losses for homeowners in colder regions.

Ways To Improve Heat Pump Performance In Winter

Enhancing your heat pump’s performance not only improves comfort but also controls utility costs during cold weather.

Regular Maintenance Matters

Change air filters monthly during heating season.
Keep both indoor and outdoor coils clean. Remove snow, ice, or debris from the exterior unit.
Schedule annual professional inspections to check refrigerant levels, electrical components, and defrost controls.

Optimize Thermostat Settings

Set the thermostat to a consistent temperature to avoid large swings, as frequent adjustment can trigger auxiliary heat.
Use programmable or smart thermostats designed for heat pump use to prevent unnecessary backup heat activation.

Improve Home Insulation

Seal air leaks around doors, windows, and penetrations.
Upgrade attic and wall insulation to lower heat loss.
Install energy-efficient windows or use plastic film insulation kits in winter.

Upgrade Or Supplement System If Needed

If your unit is over a decade old or undersized, consider replacing with a cold-climate rated heat pump.
In extreme cases, consider supplemental heating like a high-efficiency gas furnace in a dual-fuel system.

Preventive maintenance and home weatherization are the best strategies to ensure efficiency during cold snaps.

How To Tell If Your Heat Pump Is The Correct Size

A properly sized heat pump balances comfort, efficiency, and energy use. Sizing is measured in British Thermal Units (BTUs) per hour, based on home size, climate, and insulation levels.

Professional HVAC contractors use calculations (Manual J load calculation) to accurately size equipment.
Units that are too small will run constantly and never quite achieve target temperature, particularly in winter.
Oversized units cycle too frequently, reducing efficiency and lifespan.

If your home is routinely uncomfortable in both summer and winter despite non-stop operation, a sizing assessment is recommended.

Understanding Auxiliary Heat And Defrost Cycles

Auxiliary Or Emergency Heat

Heat pumps use electric resistance coils or a backup furnace when they can’t keep up with demand.
This auxiliary heat is much less efficient than the heat pump and can drastically raise energy bills if used too often.

Defrost Mode

In freezing weather, frost can build up on the outdoor coil.
The system temporarily switches to cooling mode to melt the ice, which may make indoor air feel cooler briefly.
Frequent or very long defrost cycles can indicate a problem with sensors or components.

Learning to recognize when auxiliary heat or defrost cycles engage can help identify inefficiencies or maintenance needs.

Frequently Asked Questions About Heat Pump Operation In Winter

Can A Heat Pump Be Used All Winter In The Northern U.S.?
Yes, especially modern cold-climate heat pumps, though auxiliary or supplementary heating may be required in extreme cold.

Will My Heat Pump System Wear Out Faster If It Runs All The Time?
Not necessarily. Heat pumps are designed for long run cycles. Frequent, rapid cycling is harder on the equipment than steady operation.

Is It Cheaper To Switch To Emergency Heat During Cold Snaps?
No. Electric resistance heat (emergency heat) is less efficient and more expensive than running the main heat pump, even at low temperatures, unless a dual-fuel system is installed.

How Do I Know If My Heat Pump Has A Problem Or Is Just Working Hard?
If indoor comfort is maintained, bills are in line with expectations, and there are no system alarms, it’s likely operating normally. If not, call a professional for evaluation.

Heat Pump Maintenance Checklist For Winter Performance

Task	Frequency	Why It Matters
Replace Air Filters	Every 30-60 days	Improves airflow and system efficiency
Clear Snow/Ice/Debris	After storms or weekly	Prevents airflow restriction and icing
Inspect Air Ducts	Seasonally	Reduces heat loss and boosts output
Professional Tune-Up	Annually	Ensures refrigerant levels, sensors, and controls are set optimally
Monitor Thermostat	Continuous	Ensures accurate temperature control and minimizes auxiliary heat

When To Consider Upgrading Your Heat Pump

Frequent or constant auxiliary heat use, even after improving sealing and insulation, may indicate your unit is improperly sized or outdated.
If repairs exceed a third of replacement costs or the system is over 12-15 years old, new models offer improved performance and efficiency in cold climates.
Look for ENERGY STAR-certified cold climate heat pumps (ccASHPs) with higher HSPF and COP ratings.

Upgrades can pay off in lower utility bills, better comfort, and modern features like smart controls and zoning.

Choosing The Right Heat Pump For Cold Weather

For homeowners in rigorous winter regions like the Northeast, Midwest, or Mountain West, selecting the right equipment is vital.

Inverter-driven compressors adjust output for efficiency and consistent heating even at low temperatures.
Models with enhanced vapor injection or variable-speed blowers manage airflow and comfort even in deep cold.
Review product labels for performance at 5°F or lower (Low Temperature or “Heating Capacity at 5°F”).

Look for manufacturer data and third-party reviews that verify performance during extended periods below freezing.

How To Reduce Heat Pump Energy Costs In Cold Weather

Only lower thermostats by 2-3°F at night, as deeper setbacks can trigger auxiliary heat during recovery.
Close blinds and curtains overnight to reduce radiant heat loss.
Avoid blocking indoor registers or outdoor units with furniture, drapes, or snow.
Consider adding supplemental targeted heating (like a ductless mini-split for a main living area) to reduce strain on the primary system during cold snaps.

Even small adjustments and habits can make a meaningful impact on comfort and energy savings.

Summary Table: Key Points On Heat Pump Performance In Winter

Factor	Impact	What To Do
Outdoor Temperature Drops Below 32°F	Runs for longer cycles, may use auxiliary heat	Monitor, but normal unless comfort or bills are affected
Dirty Filters/Coils	Reduces efficiency, increases run time	Replace filters, clean coils monthly
Poor Insulation	Heat loss makes system run constantly	Seal leaks, add insulation, upgrade windows
System Sizing Issue	Can’t meet heat demand	Schedule Manual J load calculation with a professional
Old/Efficient Unit	High energy use in cold weather	Replace with cold climate-optimized model
Frequent Auxiliary Heat	Higher electric bills	Optimize thermostat, improve efficiency, consider upgrades

Where To Find More Information

Understanding why your heat pump runs constantly in cold weather and taking practical steps to optimize performance will keep your home comfortable and your energy bills in check all winter long.