Do Heat Pumps Work in Cold Weather? 9 Facts for BC Homes

Do Heat Pumps Work Below Freezing?

Modern heat pumps can continue heating when outdoor temperature falls below 0°C. Many cold-climate systems are designed to operate at temperatures near -25°C, and certain models have published operating ranges below that point.

The minimum operating temperature does not tell the whole story. A model may continue running at a very low temperature while producing less heat than the home needs.

Three separate questions should be considered:

1. Can the heat pump continue operating at the outdoor temperature?
2. How much heating capacity can it produce at that temperature?
3. Is that capacity enough to match the home’s heat loss?

The third question is the most important. A correctly selected system must be compared with the building’s heating requirement at the local winter design temperature.

Outdoor temperature ratings, building heat loss and backup capacity must be evaluated together.

Fact 1: Cold Outdoor Air Still Contains Heat

A heat pump does not create most of its heat through electric resistance. It uses electricity to operate the compressor, fans, pumps and controls while moving heat from outside to inside.

During heating mode:

1. Cold refrigerant enters the outdoor coil.
2. The refrigerant absorbs heat from outdoor air.
3. The compressor raises the refrigerant pressure and temperature.
4. Hot refrigerant travels to the indoor coil.
5. The indoor coil releases heat into the home.
6. The refrigerant pressure drops before the cycle starts again.

This process can continue below freezing because outdoor air still contains thermal energy. The system uses refrigerant properties and pressure changes to collect and concentrate that energy.

In summer, the reversing valve changes the direction of refrigerant flow. The indoor coil absorbs heat from the home and the outdoor coil releases it outside. This allows one system to provide both heating and air conditioning.

Better Homes BC describes a heat pump as an electric heating and cooling system that transfers heat rather than producing it through combustion. You can review its official explanation of how a heat pump works.

Fact 2: Heating Capacity Usually Drops as the Temperature Falls

A heat pump may operate very well during mild winter weather but deliver less heating output during a colder period.

This happens for several reasons:

• There is less usable heat available in colder outdoor air.
• The compressor must create a larger temperature and pressure difference.
• Frost may form on the outdoor coil.
• Defrost cycles temporarily interrupt normal heating.
• The home loses heat more quickly as outdoor temperature falls.

The heat pump’s available capacity is moving downward at the same time the building’s heating requirement is moving upward.

The temperature where these two lines meet is often called the balance point.

Thermal Balance Point

The thermal balance point is the outdoor temperature where the heat pump’s available heating capacity equals the home’s heating load.

Above that temperature, the heat pump can normally meet the full heating requirement. Below it, supplemental heat may be needed unless the system was selected to maintain enough low-temperature capacity.

Economic Balance Point

A dual-fuel system may also use an economic balance point. This control setting determines when operating the gas furnace becomes more economical or practical than continuing with the heat pump.

The economic balance point depends on:

• Electricity rates
• Gas rates
• Heat pump efficiency
• Furnace efficiency
• Outdoor temperature
• Control strategy

The thermal and economic balance points are not always the same.

Fact 3: Cold-Climate Heat Pumps Are Designed for Lower Temperatures

A cold-climate heat pump is designed to maintain stronger heating performance when outdoor temperature falls well below freezing.

Depending on the model, cold-climate features may include:

• Variable-speed inverter compressors
• Enhanced vapour injection
• Larger outdoor heat exchangers
• Improved refrigerant controls
• Base-pan or drain protection
• Advanced defrost controls
• Low-temperature compressor protection
• Controls that adjust capacity in smaller increments

Variable-capacity equipment can increase compressor speed as the heating load rises. It can also reduce output during mild weather instead of repeatedly switching fully on and off.

Cold-Climate Labels Need Context

A cold-climate designation is useful, but it does not prove that every listed model will heat every home without backup.

ENERGY STAR cold-climate criteria evaluate low-temperature efficiency and capacity. Current criteria include performance testing at 5°F, approximately -15°C. The equipment must demonstrate specified efficiency and retain a defined percentage of its milder-weather capacity at that test condition.

Homeowners can review the official ENERGY STAR heat pump product criteria.

These ratings help compare equipment, but the contractor must still compare the selected model’s performance with the home’s calculated heating load.

Fact 4: Heat Pump Performance Depends on Where You Live in BC

British Columbia does not have one winter climate. Equipment that easily handles a typical winter day in Vancouver may require a different design strategy in Prince George, Kamloops or Fort St. John.

Metro Vancouver and the Fraser Valley

Most winter conditions in Vancouver, Burnaby, Richmond, Surrey, Coquitlam and nearby communities are within a range where modern heat pumps can operate effectively.

These areas still experience cold snaps. Home design must account for occasional lower temperatures, not only the average winter day.

Local performance also varies because of:

• Elevation
• Wind exposure
• Proximity to the water
• Home age
• Insulation
• Window condition
• Air leakage
• Number of exposed exterior walls

A newer Burnaby townhouse and an older detached Vancouver home may need very different system capacities even when their floor areas are similar.

Fraser Valley Conditions

Parts of Langley, Abbotsford, Mission and Maple Ridge can experience colder overnight temperatures than central Vancouver. Detached homes may also have larger floor areas, more exterior exposure and longer duct systems.

System selection should reflect local design temperature and the specific property rather than using one Lower Mainland rule for every home.

Interior and Northern British Columbia

In colder BC regions, low-temperature heating capacity becomes more important. A cold-climate model, larger system, improved building envelope or planned backup heat may be required.

Backup heating does not mean the heat pump has failed. It can be part of the intended design for the coldest hours of the year.

Fact 5: Nominal Tonnage Does Not Show Winter Heating Performance

A heat pump described as two tons, three tons or four tons is usually classified using nominal cooling capacity.

One ton represents approximately 12,000 BTU per hour. A three-ton system is commonly associated with approximately 36,000 BTU per hour of nominal cooling capacity.

That number does not guarantee 36,000 BTU per hour of heating at every outdoor temperature.

The actual heating output may change according to:

• Outdoor temperature
• Indoor temperature
• Compressor speed
• Indoor and outdoor airflow
• Matched indoor equipment
• Refrigerant-line length
• Defrost operation
• System controls

What to Request From the Contractor

Ask for the selected system’s published heating capacity at temperatures relevant to your location.

Useful performance points may include:

• 8°C or 47°F
• 0°C or 32°F
• -8°C or approximately 17°F
• -15°C or 5°F
• The local winter design temperature

The quote should identify the complete matched system, including the outdoor unit, indoor coil, air handler or furnace.

Comparing only the outdoor-unit model can produce an inaccurate result because different indoor combinations may have different capacity and efficiency ratings.

Fact 6: Defrost Mode Is a Normal Part of Winter Operation

During heating mode, the outdoor coil becomes cold. Moisture in the outdoor air may freeze on the coil and create a layer of frost.

A light frost layer is normal. Heavy frost restricts airflow and reduces the coil’s ability to collect heat.

To remove the frost, the system temporarily enters defrost mode.

What Happens During Defrost?

Depending on the equipment and controls:

• The reversing valve temporarily changes refrigerant direction.
• Hot refrigerant flows through the outdoor coil.
• The outdoor fan may stop.
• Steam or water may appear around the outdoor unit.
• Indoor air may feel cooler for a short period.
• Electric auxiliary heat or a furnace may operate during the cycle.

A short cloud of steam from the outdoor unit during defrost is usually normal. It should not automatically be mistaken for smoke or a refrigerant leak.

How Often Should Defrost Occur?

The frequency depends on outdoor temperature, humidity, coil condition and the control system.

Cold and damp Lower Mainland weather can create favourable conditions for frost formation even when the outdoor temperature is only slightly below freezing.

Repeated or unusually long defrost cycles may point to:

• A dirty outdoor coil
• Restricted outdoor airflow
• A damaged temperature sensor
• A control-board problem
• Incorrect refrigerant charge
• A reversing-valve problem
• Poor outdoor-unit placement

The outdoor unit should not remain trapped inside a solid block of ice.

Fact 7: Some Homes Need Backup Heat During Cold Weather

Backup heat provides additional capacity when the heat pump cannot meet the full heating load, during defrost or after a large thermostat change.

The most common backup arrangements are electric auxiliary heat and dual-fuel heating.

Electric Auxiliary Heat

A central air handler may contain electric resistance heating elements. These elements can operate in stages when additional heat is required.

Electric auxiliary heat provides dependable output but normally uses more electricity per unit of delivered heat than the heat pump compressor.

Frequent auxiliary heat operation may result from:

• Very cold outdoor conditions
• An undersized heat pump
• A large thermostat setback
• Poor insulation or air sealing
• Restricted airflow
• Incorrect control settings
• Equipment or refrigerant problems

Dual-Fuel Heat Pump and Furnace

A dual-fuel system combines a central heat pump with a compatible gas furnace.

The heat pump handles cooling and usually supplies heat during mild and moderately cold weather. The furnace takes over according to a selected outdoor-temperature or control setting.

This arrangement may suit homeowners who:

• Already have a relatively new gas furnace
• Want central air conditioning and efficient shoulder-season heating
• Have a home with a high winter heating load
• Prefer gas backup during colder conditions
• Need a staged transition away from existing equipment

Better Homes BC explains how a dual-fuel central ducted heat pump uses a backup furnace during selected colder conditions.

Backup Heat Should Be Designed, Not Improvised

The contractor should determine:

• The amount of backup capacity required
• The temperature where backup heat is enabled
• Whether the heat pump and backup can operate together
• How defrost heat will be provided
• Whether the electrical service can support resistance heat
• How controls will prevent unnecessary backup use

Fact 8: Correct Sizing Is More Important Than Choosing the Largest Unit

A larger heat pump may provide more cold-weather capacity, but oversizing can create new problems during mild weather and summer cooling.

An oversized system may:

• Cycle on and off too frequently
• Create noticeable temperature swings
• Produce louder airflow
• Remove less summer humidity
• Operate below its efficient modulation range
• Cost more to purchase

An undersized system may:

• Run continuously during colder weather
• Use backup heat more often
• Fail to maintain the selected temperature
• Recover slowly after thermostat changes

What a Heat-Load Calculation Should Consider

• Floor area and ceiling height
• Wall, ceiling and floor insulation
• Window size, type and orientation
• Air leakage
• Number of floors
• Basement and crawl-space conditions
• Solar heat gain
• Building exposure
• Local winter design temperature
• Internal heat gains

The heating load should then be compared with the heat pump’s published low-temperature capacity.

Using only floor area or the size of the old furnace is not enough. Gas furnaces are frequently oversized, so copying the furnace’s BTU rating may produce an oversized heat pump.

Fact 9: Ducted and Ductless Systems Behave Differently in Winter

Ducted Heat Pumps

A central ducted heat pump distributes heated air through supply ducts and returns indoor air through a return system.

Winter performance depends on:

• Supply duct size
• Return-air capacity
• External static pressure
• Filter pressure drop
• Blower setup
• Duct leakage
• Duct insulation
• Register and grille sizing

Heat-pump supply air often feels less intensely hot than gas-furnace air. The system typically maintains comfort through longer, steadier operating cycles.

Low airflow can reduce capacity, increase compressor pressure, create noise and cause equipment faults.

Ductless Heat Pumps

A ductless system delivers heated air directly from one or more indoor units.

Ductless performance depends on:

• Indoor-unit location
• Room layout
• Open or closed doors
• Air circulation between spaces
• Indoor-unit capacity
• Outdoor-unit capacity
• Connected combination limits

One wall-mounted unit may heat an open living area effectively but may not provide equal comfort inside several closed bedrooms.

Multi-zone systems require careful selection. Connecting many indoor units does not mean the outdoor unit can deliver every indoor unit’s full rated capacity at the same time.

How to Operate a Heat Pump During Cold Weather

Heat pumps often perform best with steady operation rather than frequent large thermostat changes.

Use a Stable Temperature

Choose a comfortable setpoint and allow the system to maintain it. A large overnight setback can trigger auxiliary heat or require a long recovery period in the morning.

Select Heating Mode

Use the dedicated heating setting during winter. Automatic changeover mode may switch between heating and cooling during unusual temperature changes or because of heat from sunlight and indoor activities.

Keep Filters Clean

Dirty filters reduce airflow and may lower capacity. Check ductless filters regularly and replace central-system filters according to the equipment and filter type.

Keep the Outdoor Unit Clear

Maintain airflow around the outdoor coil. Remove leaves, vegetation and loose debris without damaging the fins.

Do not block the unit with temporary covers. Do not chip ice from the coil with sharp tools.

Protect Drainage

Defrost water must drain away safely. The equipment should be elevated and positioned so water does not refreeze around the base, walkway or building foundation.

Avoid Unnecessary Emergency Heat

Emergency heat usually disables normal heat-pump operation and relies on the backup source. It should generally be used only when the compressor system has failed or when instructed by a technician.

Emergency heat and auxiliary heat are not the same:

• Auxiliary heat may operate automatically with the heat pump.
• Emergency heat is a manual operating mode intended for specific situations.

Cold-Weather Operation: What Is Normal and What Needs Service?

Call for Service When:

• The heat pump does not maintain temperature
• The outdoor coil remains heavily iced
• The breaker repeatedly trips
• The system displays a fault code
• The outdoor fan does not operate
• The compressor repeatedly starts and stops
• There is a burning or electrical smell
• The system runs only on emergency heat
• Energy use rises sharply without a weather explanation
• Water or ice creates a safety hazard

Cold-Weather Heat Pump Checklist

Use this checklist before and during the heating season:

• Confirm the thermostat is set to Heat.
• Use a steady indoor temperature.
• Clean or replace indoor filters.
• Keep furniture and curtains away from supply and return grilles.
• Keep ductless indoor units unobstructed.
• Remove leaves and loose debris near the outdoor unit.
• Check that defrost water can drain safely.
• Do not cover the outdoor unit.
• Do not break ice from the coil with tools.
• Notice whether backup heat runs only when expected.
• Arrange service when heavy ice remains on the unit.
• Schedule professional maintenance according to the system requirements.

Planning a Heat Pump for a BC Home

Before selecting equipment, the contractor should evaluate:

• The home’s heating and cooling loads
• Low-temperature equipment capacity
• Ductwork or indoor-unit locations
• Electrical service and panel capacity
• Existing furnace, boiler or baseboard heating
• Backup-heating requirements
• Outdoor-unit location
• Defrost drainage
• Noise and property clearances
• Permit requirements

The best system is not always the model with the highest nominal capacity or efficiency rating. It is the system that matches the home, climate, distribution system and operating plan.

ENERGY STAR provides additional guidance about air-source heat pumps and cold-climate performance.

Heat Pump Installation in Metro Vancouver and Fraser Valley

Bernoulli Heating and Cooling provides heat pump installation assessments for ducted, ductless, multi-zone, cold-climate, full-electric and dual-fuel systems.

Before preparing a proposal, we review the home, existing heating equipment, airflow, ductwork, electrical requirements, outdoor-unit location and installation access.

New installation estimates are free. Diagnostic appointments for existing heat-pump systems are $135.

Call 604-518-4438 or email heatingbernoulli@gmail.com to arrange an assessment.

Local heat pump installation guides:

• Heat Pump Installation Vancouver
• Heat Pump Installation Burnaby
• Heat Pump Installation Surrey