It is the middle of January in Ottawa. You look outside and see your heat pump surrounded by a cloud of white vapor. A loud “whoosh” sound follows, and a few minutes later you notice water pooling beneath the unit.
If this scenario has you wondering whether your system is malfunctioning, you are not alone. These winter behaviors are often mistaken for serious mechanical failures, but in most cases, they are just part of your heat pump’s Defrost Cycle—a completely normal process designed to keep your home warm during freezing temperatures.
Key Takeaways: What You Need to Know
- White “Smoke” is Normal: It is actually steam created when the unit melts ice off its outdoor coils.
- Loud Noises are Normal: A “whooshing” sound occurs when the internal valve reverses direction to start the defrost process.
- Backup Heat is Automatic: Your thermostat may say “Aux Heat On” to keep you comfortable while the heat pump defrosts.
- When to Call Us: If the unit is encased in solid ice or steams for more than 30 minutes, you may need heating repair services.
Understanding the Heat Pump Defrost Cycle
Modern cold-climate heat pumps, like the Lennox and Moovair models we install, are built to handle Ottawa winters. However, even the best systems have to deal with physics.
When your heat pump runs in heating mode, the outdoor coil gets colder than the air outside. Moisture in the air freezes onto this coil, forming frost. If this ice were allowed to build up, it would block airflow and stop the unit from heating your home. To prevent this, your system automatically switches into “Defrost Mode.”
Here is exactly what that looks (and sounds) like.
1. White “Smoke” = Steam from Melting Ice
What you see: A cloud of white vapor rising from the outdoor unit. What is happening: During defrost, the system temporarily reverses into cooling mode. This sends hot refrigerant to the outdoor coil to melt the frost instantly. That “smoke” is simply the steam from the melting ice hitting the cold winter air. Verdict: Normal. The steam should dissipate within 5 to 15 minutes.
2. Loud “Whoosh” or “Swoosh” Sound
What you hear: A sudden rush of air, a “clunk,” or a sound similar to air brakes releasing. What is happening: This is the sound of the Reversing Valve physically sliding to change the direction of the refrigerant flow. It typically happens at the very beginning and very end of the cycle. Verdict: Normal. A single, short-duration sound is expected.
3. Water or Ice Accumulation Below the Unit
What you see: Drips, puddles, or frozen patches on the pad directly under the unit. What is happening: Gravity is doing its work. As the ice melts off the coil, it drips down. In deep freeze conditions, this water may refreeze on the concrete pad. Verdict: Normal. However, you should monitor this.
- Maintenance Tip: Ensure the ice does not build up high enough to encase the bottom of the unit. If necessary, gently remove ice buildup around the base using warm water, but never use sharp tools or force on the coils.
4. “Aux Heat” Displayed on Thermostat
What you see: Your thermostat (such as a Lennox S40 or Ecobee) displays “Auxiliary Heat On.” What is happening:Because the heat pump is technically in cooling mode to melt the outdoor ice, it would blow cold air into your house if left alone. To prevent this, the system automatically fires up your backup heat source (gas furnace or electric strip) to temper the air. Verdict: Normal. This ensures your indoor comfort does not drop during the cycle.
When to Call AirZone for Heat Pump Service
While most defrost behaviors are standard, there are warning signs that indicate a malfunction. You should contact our service department if you notice:
- Solid Ice Block: The outdoor unit is fully encased in thick ice, and air cannot pass through the fins.
- Excessive Duration: The unit steams or stays in defrost mode for longer than 30 minutes.
- Loss of Heat: Your home temperature is dropping, and the auxiliary heat is not engaging to assist.
- Mechanical Noises: You hear metal-on-metal grinding, screeching, or violent vibrations (distinct from the standard “whoosh”).
Why Homeowners Trust AirZone HVAC Services
We have installed and serviced thousands of heat pumps throughout Ottawa, Kanata, Orleans, and Barrhaven. As certified experts for Lennox, Moovair, and Mitsubishi, we understand how these systems are engineered to operate in our specific climate.
- Fast Response: We offer diagnostic services to get your heat back on quickly.
- Local Expertise: Our technicians are factory-trained and directly employed—we don’t use subcontractors.
- Comprehensive Support: From new installations to emergency repairs, we are a full-service partner for your home.
Get Professional Help When You Need It
If your heat pump is showing signs of trouble—or if you just need reassurance that everything is running smoothly—contact the local experts Ottawa trusts.
Call: 613-592-5770 Text: 613-706-3381 Request Service: Book Online Here
