Common Heat Pump Problems Canadians Face in Winter

Modern cold-climate heat pumps are incredibly well-engineered, and for most of the year they handle Canadian temperatures with ease. But winter in Canada is in a league of its own. Between sudden cold snaps, long stretches of sub-zero temperatures, and the kind of heavy humidity that encourages frost buildup, even a properly installed and well-sized heat pump can have moments where it struggles to keep up.

The challenge isn't just the weather, it's also the environment these systems operate in. Canada's housing stock is unusually diverse, and that plays a big part in heat pump performance. Older Toronto homes with drafty basements and uninsulated additions behave very differently from tightly sealed high-efficiency builds. Rural cottages often face strong winds, drifting snow, and colder microclimates that push equipment harder than expected. Even two identical heat pumps can perform differently depending on where they're installed and how air flows around the property.

These factors don't mean your heat pump is failing, they simply highlight how demanding our winters can be. Most common winter performance issues are predictable and preventable with a bit of seasonal care. A quick checkup before temperatures drop can go a long way toward keeping your system running smoothly, efficiently, and reliably all winter long.

How Cold-Climate Heat Pumps Are Designed to Work in Winter

Cold-climate heat pumps (ccASHPs) are built very differently from the older-generation heat pumps many homeowners still remember. Today's systems use advanced inverter-driven compressors, variable-speed fans, and smarter defrost controls that allow them to operate efficiently even when temperatures plunge well below freezing. In moderate weather, they run quietly and with remarkable efficiency, but winter introduces extra challenges that are unique to Canada.

At the heart of winter performance is the inverter compressor. Instead of turning on and off repeatedly like older systems, it adjusts its speed to deliver exactly the amount of heat your home needs. This helps maintain consistent indoor temperatures, reduces energy waste, and keeps the system from working harder than necessary during milder days. The technology has come a long way, many 2024–2025 cold-climate models can now deliver reliable heat at –20°C, and some can handle temperatures approaching –30°C.

Still, no matter how advanced the equipment, winter weather can throw curveballs. High humidity during cold spells increases frost accumulation on the outdoor unit, causing more frequent defrost cycles. Wind chills affect how quickly frost forms and how much heat the unit has to pull from the outdoor air. Rapid temperature swings, which are increasingly common across Ontario and other parts of Canada, force the system to constantly adjust its output, sometimes leading to short-term dips in performance.

Another factor many homeowners don't realize: heat pump performance varies significantly depending on the type of home it's supporting.

• Older Toronto homes tend to have colder basements, drafty rooms, or additions that weren't built to modern insulation standards, all of which increase heating demand.
• Rural homes and cottages face harsher exposure, drifting snow, wind tunneling around the outdoor unit, and wide day-to-night temperature swings.
• Newer high-efficiency homes retain heat well, but restricted airflow or improper ventilation can still impact performance.

All of this means that even the best cold-climate heat pump will occasionally work harder, run longer, or cycle into defrost more often during winter. These aren't always signs of a problem, they're normal reactions to Canadian weather.

Of course, a well-maintained system handles winter stress far better than one that hasn't been inspected in years. A simple seasonal checkup ensures sensors, drain paths, and airflow are working properly, helping prevent the most common cold-weather issues before they show up.

Problem #1: Heat Pump Freezing or Icing Up

A light layer of frost on your outdoor heat pump unit is completely normal in winter, but thick ice buildup or a unit that freezes solid is a sign something isn't working the way it should. In Canadian winters, this is one of the most common issues homeowners encounter, especially during long stretches of cold, damp weather.

Heat pumps pull heat from the outdoor air, and in doing so, moisture naturally condenses on the coil. When temperatures dip, that moisture freezes, especially when the air is humid. Canadian winters often combine both cold and humidity, creating the perfect recipe for frost.

Your heat pump is designed to handle this through an automatic defrost cycle that periodically melts frost by reversing the flow of refrigerant. But when something disrupts airflow or interferes with defrost timing, frost can accumulate faster than the system can melt it.

Common Causes of Excessive Ice Buildup

• Blocked airflow: Snow, leaves, or ice around the outdoor unit restricts air movement, causing the coil to freeze faster.
• Faulty or inaccurate defrost sensor: If the sensor doesn't detect ice properly, the unit won't switch into defrost when it needs to.
• Fan issues: A failing or frozen fan blade can't move air across the coil.
• Drainage problems: A tilted unit, clogged drain holes, or ice buildup underneath can trap water and re-freeze around the base.
• Prolonged cold + high humidity: Common in Ontario during storms or early winter thaws, creating more frost than usual.

Homeowner Checklist

Before assuming something major is wrong, there are a few simple steps you can take:

• Clear snow and ice at least 2–3 feet around the unit
• Check for obstructions like leaves, branches, or fencing
• Ensure the outdoor unit is elevated enough to prevent snow accumulation
• Look for ice blocking the fan (never chip it away, let it melt naturally)
• Listen for the sound of the defrost cycle (a "whoosh" followed by a pause is normal)

Sometimes the solution is as straightforward as clearing airflow.

When to Call a Professional

If the unit is completely encased in ice, refuses to go into defrost, or the fan isn't turning, it's time to call a professional. Thick ice puts enormous strain on the coil, compressor, and refrigerant lines, and running the system in that condition can lead to expensive repairs.

The easiest way to avoid freezing issues is ensuring the system's sensors, drainage, and airflow are all working properly before winter begins. A simple seasonal checkup catches small issues long before they turn into a frozen outdoor unit.

Problem #2: Heat Pump Running Constantly or Not Keeping Up with the Cold

It can be worrying to see your heat pump running non-stop in winter, but here's an important reassurance: during Canadian cold snaps, this is completely normal. Heat pumps are designed to run longer at lower outdoor temperatures to maintain steady indoor comfort. Unlike furnaces that blast heat in short bursts, heat pumps work by moving heat gradually and efficiently.

That said, there are situations where constant runtime or insufficient heating signals a deeper issue, especially if your home feels chilly despite the system working hard.

Modern cold-climate heat pumps are engineered to deliver consistent, even heat. During particularly cold days (or nights), they may:

• Maintain low, steady operation to reduce energy spikes
• Adjust compressor speed to match heating demand
• Run continuously to replace heat lost through walls, floors, or older insulation

This is normal behaviour, especially in older Toronto homes, older cottages, or properties with draft-prone basements.

Common Causes of Heat Pump Running Constantly

If your heat pump still can't keep up despite running continuously, or rooms feel noticeably cooler than usual, one of the following issues could be at play:

• Dirty or clogged filters reducing airflow
• Airflow restrictions such as closed vents or blocked returns
• Indoor coil dust buildup slowly reducing heating output
• Low refrigerant causing poor heat transfer
• Aging components struggling under winter load
• Undersized system, common in older retrofits or homes with major heat loss

Sudden cold snaps are common across Ontario and can reveal installation or airflow weak points that didn't show up earlier in the season.

Homeowner Checklist

Before calling a technician, homeowners can try a few quick steps:

• Replace or clean filters (winter airflow drops noticeably as filters clog faster)
• Keep all vents open, especially in rooms far from the thermostat
• Inspect the outdoor unit to ensure snow isn't restricting air intake
• Check that the thermostat isn't fighting space heaters or closed doors

A system that's fighting airflow restrictions will run harder and longer than necessary.

When to Call a Professional

If the heat pump consistently falls behind, even during moderate winter temperatures, it's a sign that something deeper needs attention:

• Heat output feels weaker than usual
• The system runs non-stop but temperature continues dropping
• Electric backup heat or emergency heat activates frequently
• You notice new noises during long run cycles

In these cases, a technician can test refrigerant levels, evaluate airflow, inspect sensors, and verify that the system's capacity matches your home's heat loss.

A quick pre-winter tune-up is often all it takes to avoid these performance dips. Ensuring filters, coils, sensors, and fans are working at peak efficiency helps your heat pump stay ahead of the cold without overworking itself. Even newer cold-climate units benefit from a seasonal check to handle Canada's unpredictable winter swings.

Problem #3: Cold Air Coming from Vents

Feeling a blast of cool air from your vents in the middle of winter can be frustrating, and a little alarming, but it doesn't always mean your heat pump is failing. In fact, this is one of the most common winter questions homeowners ask, and in many cases, the explanation is completely normal.

Heat pumps simply work differently than furnaces. Instead of producing hot, dry air in short bursts, they deliver a steadier, gentler stream of warm air. Because the air isn't "furnace hot," it can sometimes feel cool on your skin even when it's actually heating your home.

Common Causes of Cold Air Coming from Vents

A few everyday reasons can make the air feel cooler than expected:

• Defrost Mode Activation
  During the defrost cycle, the heat pump temporarily reverses operation to melt frost on the outdoor coil. It may blow noticeably cooler air for a few minutes, this is normal and protects the system from ice buildup.
• Moderate Supply Air Temperature
  Heat pump supply air is typically around 90–100°F (32–37°C), much lower than furnace temps, which can reach 120°F+. The heat is still there, it's just gentler.
• Thermostat Sensing Differences
  Smart thermostats or older wall units may sense room temperature differently depending on their placement, causing the system to adjust airflow more frequently.
• Drafts or Cold Rooms
  Older Toronto homes, additions, and drafty basements often create cooler airflow patterns that make warm air feel cold.

While occasional cool air is normal, consistently cold airflow may point to an issue such as:

• Low refrigerant
• Dirty or blocked indoor coils
• Clogged filters restricting heat transfer
• Fan or blower issues
• Malfunctioning reversing valve
• Heat pump not entering or exiting defrost mode properly

These issues reduce how effectively the heat pump can absorb or deliver heat, creating airflow that feels lukewarm or outright cold.

Homeowner Checklist

Before assuming the worst, try these simple steps:

• Change or clean the filter
  Dirty filters are a leading cause of weak or cool airflow in winter.
• Ensure vents and returns are fully open
  Closed vents or blocked return grills restrict heat distribution.
• Check for drafts around windows and doors
  Even efficient heat pumps struggle against major heat loss.
• Wait a few minutes
  If the system just entered defrost mode, it will cycle back to heating shortly.

When to Call a Professional

Cool air that lasts longer than a typical defrost cycle or fails to improve after filter changes often indicates a refrigerant or sensor issue. These require professional tools and testing to diagnose accurately.

Many of the causes behind cold airflow, blocked coils, low refrigerant, faulty valves, are issues that develop slowly. A seasonal maintenance visit catches these early, ensuring your heat pump delivers the warm, steady airflow it was designed for, even on Ontario's coldest days.

Problem #4: Heat Pump Freezing Indoors (Evaporator Coil Icing)

While most people expect ice to form on the outdoor unit in winter, indoor freezing is a very different issue, and almost always a sign that something isn't working correctly. When the evaporator coil inside the air handler ices over, airflow drops dramatically, cooling efficiency plummets, and the system may eventually shut down to protect itself.

This problem often appears during sudden temperature swings, long cold spells, or periods of high indoor humidity, all common across Canadian winters.

The evaporator coil is responsible for absorbing heat from your home's air. To do that efficiently, it needs:

• Clean, unobstructed airflow
• Stable refrigerant levels
• Balanced temperatures across the coil

When one of these factors is off, the coil can get too cold. Combine that with winter dryness or uneven humidity levels, and frost can form rapidly.

Common Causes for Indoor Coil Icing

Common causes include:

• Low refrigerant levels
  This reduces the pressure inside the coil, causing it to drop below freezing.
• Dirty or clogged filters
  Restricted airflow means less warm air passes over the coil, allowing its temperature to fall too low.
• Blocked or dusty indoor coils
  Dust acts like insulation, trapping cold air and encouraging ice formation.
• Closed or obstructed vents
  When the system can't circulate air properly, parts of the coil overcool.
• Blower or fan issues
  If the indoor fan is running too slowly, or not running at all, cold air lingers around the coil.

Indoor freezing is more common in Canada for a few unique reasons:

• Dramatic temperature swings (e.g., –10°C one day, +5°C the next) disrupt humidity balance.
• Older homes with inconsistent insulation cause uneven temperatures across rooms and ducts.
• Long heating runs during deep freezes push coils harder and can expose weak components.

These conditions make small airflow or refrigerant issues more noticeable, and more likely to cause icing.

Homeowner Checklist

Indoor coil icing often starts subtly before becoming obvious. Watch for:

• Airflow suddenly weakening
• Vents blowing cooler than usual
• Water dripping from the unit (melted ice)
• The system running louder during long cycles
• Frost visible around the air handler housing

If you catch it early, turning off the system and letting the coil thaw can prevent further strain.

Continued freezing can:

• Damage the compressor
• Cause refrigerant floodback (very costly)
• Strain the blower motor
• Trigger full system shutdowns
• Lead to water leaks when thawing occurs

Ice is one of the fastest ways for a small problem to become a major repair.

When to Call a Professional

If ice returns after thawing, or the system freezes repeatedly, it's a clear sign something deeper is wrong. Low refrigerant and airflow issues require specialized tools to diagnose safely; it's not something homeowners can fix on their own.

The most common causes, dirty coils, airflow restrictions, and low refrigerant, develop gradually. Regular seasonal maintenance catches these issues early and ensures your heat pump is ready for the temperature swings and long heating runs that Canadian winters are known for.

Problem #5: Frequent Defrost Cycles

Every heat pump needs to defrost in winter. It's a normal part of cold-weather operation and keeps the outdoor coil free of frost so the system can continue absorbing heat efficiently. But when a heat pump enters defrost mode too often, stays in defrost for unusually long periods, or cycles in and out repeatedly, it's usually a sign that something isn't working the way it should.

This is one of the most common winter complaints from Canadian homeowners, especially during damp or stormy weather, so understanding what's normal and what's not can help prevent unnecessary stress or service calls.

A heat pump's defrost cycle essentially turns the system into "temporary cooling mode" to warm the outdoor coil and melt frost. During this time, indoor airflow may briefly feel cooler, the outdoor fan may stop, and you may hear a noticeable "whoosh" as the reversing valve shifts positions.

A proper defrost cycle typically lasts 3–10 minutes and activates only when frost buildup is detected.

Common Causes for Frequent Defrost Cycles

In Canada, conditions like freezing rain, heavy humidity, and back-to-back snowfalls can cause frost to accumulate faster than usual. But excessive defrosting often indicates:

• A malfunctioning defrost sensor or temperature probe
  If the sensor misreads conditions, it may trigger defrost unnecessarily.
• Faulty or sticking reversing valve
  This can cause improper switching between heating and defrost modes.
• Poorly draining outdoor unit
  Melted frost has nowhere to go, refreezing repeatedly at the base.
• Restricted airflow
  Snow, ice, or debris around the outdoor unit forces the system to protect itself by entering defrost more often.
• Dirty outdoor coil
  Dust and dirt create insulation that traps frost, causing more frequent melting cycles.
• Canadian humidity conditions
  Ontario and coastal regions often see humidity spikes even in sub-zero temperatures, which encourages rapid frost accumulation.

If your heat pump is defrosting every few minutes, or defrost cycles last unusually long, it may indicate:

• A failing reversing valve
• A faulty board or sensor
• Refrigerant issues
• A coil that's freezing too quickly
• A fan that isn't running at proper speed

These issues are difficult to diagnose without tools, so a technician should take a look.

Homeowner Checklist

If your heat pump is entering defrost mode more often than usual, try these quick steps:

• Clear snow and ice around the outdoor unit
• Inspect the top grill and coil area (from a safe distance) for ice buildup
• Remove leaves or debris blocking airflow
• Make sure gutters or roof meltwater aren't dripping onto the unit
• Check for proper drainage under the unit

Sometimes fixing airflow is enough to return the system to normal cycles.

When to Call a Professional

Many of the causes, dirty coils, poor drainage, airflow restrictions, aging sensors, are issues that gradually develop over time. A seasonal maintenance check clears debris, tests sensors, inspects airflow, and ensures the defrost cycle is working exactly as it should.

In Canadian winters, where frost and humidity are constant, a well-tuned defrost system isn't just convenient, it's essential.

Problem #6: Strange Noises in Winter

Heat pumps make a range of sounds that can seem unusual, especially if you're used to the quiet hum of summer operation. Winter brings temperature swings, frost, ice, and longer run times, all of which can create noises that catch homeowners off guard. The good news is that many winter noises are completely normal, while others are clear signs that something needs attention.

Understanding the difference helps avoid unnecessary worry and ensures real issues get addressed quickly.

These sounds are part of regular winter operation:

• The "defrost whoosh"
  A loud whooshing sound as the reversing valve switches modes is perfectly normal. It usually lasts only a moment.
• Hissing or gurgling
  Refrigerant equalizing when the system transitions between cycles.
• Cracking or popping
  This can happen when metal components expand or contract with temperature changes. It's common during extremely cold mornings.
• Louder airflow during deep freezes
  The heat pump may increase fan speed to compensate for lower outdoor temperatures.

These sounds may seem unfamiliar, but they're all part of a heat pump working hard during winter.

Common Causes for Strange Noises

Certain sounds, however, are worth paying attention to, especially in Canadian winters where ice, wind, and long runtime can stress components.

• Grinding or scraping
  Ice buildup around the fan blade or a damaged motor bearing. This is urgent, as the fan can be damaged quickly.
• Metal-on-metal clanking
  Large chunks of ice may be hitting the fan blades. This often happens after freezing rain or rapid temperature drops.
• Screeching or high-pitched squeals
  A possible blower motor or fan motor issue.
• Rapid clicking
  Relay or control board problems, especially if the system is struggling to switch modes.
• Buzzing that doesn't stop
  Could indicate electrical issues, a failing capacitor, or a compressor problem.

Winter noise complaints spike in Canada for a few reasons:

• Wind tunnel effect around older homes and cottages
• Ice storms that cause chunks of ice to form around the fan
• Drifting snow blocking airflow and stressing the motor
• Extreme cold causing metal components to contract noticeably

These environmental factors can create sounds that don't occur at any other time of year.

Homeowner Checklist

If you hear a sound that concerns you, try a few quick checks:

• Inspect the outdoor unit for ice around the fan (don't chip it, turn the system off and let it melt)
• Make sure snow isn't piled up around the sides or back of the unit
• Check for fallen branches or leaves caught in the grill
• Listen to see if the noise happens during defrost only
• Look for objects blown against the unit by wind

If the noise is irregular, loud, or gets worse, it's best not to run the system until a technician checks it.

When to Call a Professional

Contact a professional if:

• The noise is loud enough to be heard indoors
• It repeats during every cycle
• Ice buildup keeps returning
• The outdoor fan stops turning or struggles to start
• You notice reduced airflow inside when the noise starts

Ignoring these warning signs can lead to expensive repairs, especially if ice damages the fan blades or motor.

Most problematic noises are caused by airflow issues, fan obstructions, or minor component stress, all of which a seasonal maintenance visit can catch early. A quick tune-up ensures the fan, motor, and sensors are ready for Canada's extreme winter conditions, reducing the risk of mid-season surprises.

When a Winter Heat Pump Issue Means It's Time to Call a Professional

Most winter heat pump quirks are harmless and can be solved with a simple check for ice, a filter change, or a quick reset. But when symptoms become persistent, or something just doesn't feel right, it's important to bring in a professional before a minor issue turns into a major repair.

Heat pumps work hard during Canadian winters, and small performance problems can quickly escalate under prolonged strain. Knowing when DIY ends and expert help begins can save you both money and downtime during the coldest part of the season.

If you notice any of the following, it's best to have a technician take a look:

• The heat pump runs constantly and still can't maintain temperature
  This may suggest refrigerant issues, airflow problems, or an aging component that's struggling under winter load.
• Thick ice keeps building up on the outdoor unit
  Repeated freezing usually points to defrost failures, drainage issues, or sensor problems, none of which should be ignored.
• No warm air is coming from the vents
  A complete loss of heating is often caused by a refrigerant leak, compressor problem, or malfunctioning reversing valve.
• The system refuses to enter or exit defrost mode
  This typically means sensor or board issues, and further manual defrosting can risk damage.
• Unusual noises that continue or get worse
  Screeching, grinding, or loud clanking needs immediate attention.
• The backup or emergency heat kicks in frequently
  Occasional use is normal during extreme cold, but constant activation is a sign the heat pump isn't producing enough heat.
• Water leaking from the indoor unit
  This often indicates indoor coil freezing or drainage problems.

Winter demands are unforgiving, and even a high-efficiency cold-climate system can only compensate so much before bigger problems develop.

Most homeowners are surprised to learn that many winter breakdowns stem from issues that started weeks or months earlier. A simple seasonal tune-up is often enough to catch those early warning signs, improve performance, and prevent mid-winter emergencies.

Winter Heat Pump Care Checklist

A little bit of care goes a long way in helping your heat pump run smoothly through a Canadian winter. Most of the steps below take only a few minutes and can make a noticeable difference in performance, airflow, and energy efficiency. This checklist is designed for homeowners and can be used throughout the season whenever temperatures drop.

Keep Snow and Ice Away from the Outdoor Unit

• Clear at least 2–3 feet of space around all sides
• Remove drifting snow after storms
• Brush off light frost (never chip ice)
• Make sure fence lines, bushes, or snow piles aren't blocking airflow

Change or Clean Your Filters Regularly

• Check filters monthly during winter
• Replace if airflow feels weak or the filter looks dirty
• Homes with pets, renovations, or dust should check more often

Ensure All Vents and Returns Are Fully Open

• Keep vents unblocked by furniture or area rugs
• Avoid closing vents in unused rooms (this disrupts airflow)
• Check return grills for dust buildup

Inspect the Outdoor Unit After Heavy Weather

• Look for sticks, leaves, or debris caught in the top grill
• Ensure the fan spins freely
• Check for icicles or roof meltwater dripping onto the unit
• Verify the unit sits level and isn't sinking into snow or soil

Listen for Unusual Sounds

• Popping or "whooshing" is normal during defrost
• Grinding, clanking, screeching, or rapid clicking is not
• If something sounds wrong, turn the system off and inspect for ice

Keep Thermostat Settings Consistent

• Heat pumps work best with steady temperatures
• Avoid big temperature swings or dramatic adjustments
• Use smaller increments (1–2 degrees at a time)

Check Indoor Airflow

• Make sure airflow feels steady and warm
• If it suddenly weakens, check for coil freezing, blocked filters, or vent issues
• Be mindful of cold rooms or areas near drafty windows

Give the System Time After a Defrost Cycle

• Defrost cycles typically last 3–10 minutes
• Air may feel cooler temporarily
• This is normal and helps prevent outdoor freezing

If you notice repeating issues, heavy ice buildup, constant defrosting, cold air blowing for long periods, strange noises, or reduced heat output, it's time to book service. These signs often point to refrigerant, sensor, or mechanical issues homeowners can't fix on their own.

Keeping Your Heat Pump Winter-Ready

Canadian winters are tough on heat pumps, even the advanced cold-climate systems built for our extreme temperatures. Long cold snaps, humidity, frost buildup, and rapid weather swings can all make your heat pump work harder than it does at any other time of year. Most winter issues, icing, weaker heat output, frequent defrosting, unusual noises, are not signs of failure. They're often early warnings that something needs attention, or simply normal reactions to severe weather.

With a bit of care, a few quick home checks, and an understanding of how heat pumps behave in winter, you can prevent the vast majority of problems long before they start. And when something does go wrong, knowing what's normal versus what requires a professional helps protect your system and keep your home comfortable.

A seasonal tune-up is one of the simplest ways to ensure your heat pump is ready for the months ahead. It keeps sensors calibrated, airflow strong, components protected, and efficiency high, even during multi-day deep freezes. Whether your system is brand new or several years old, taking a proactive approach gives you peace of mind and helps your equipment run reliably all winter long.

If you ever have questions or notice your heat pump isn't performing quite the way it should, we're always here to help keep your home warm and comfortable when the weather turns cold.