Understanding Wintertime Freezing in Wall-Mounted Heat Pumps: A Common Yet Avoidable Issue
The Montréal winter doesn’t hold back. With temperatures plunging well below zero by December, many homeowners with wall-mounted heat pumps are surprised to discover a layer of ice on their outdoor unit by January. Yet this phenomenon is neither rare nor necessarily alarming—if it’s properly understood and managed. At AirGreen, we receive dozens of calls every year from concerned clients across Montréal, Laval, Longueuil, as well as the North Shore and South Shore, after seeing their outdoor unit iced over. This article provides real, concrete answers, detailed technical explanations, and—most importantly—proven solutions that we apply daily during our HVAC service calls.
Freezing in a Wall-Mounted Heat Pump: A Normal Occurrence… to a Certain Extent
How does a wall-mounted heat pump work in winter?
A wall-mounted heat pump pulls heat from the outside air and brings it indoors—even in the depths of winter. This heat transfer process generates condensation which, in very cold and humid conditions, can easily freeze on the outdoor unit. This kind of frost is usually temporary, as the system is designed with an automatic defrost cycle that briefly reverses the heat flow to melt the ice.
When automatic defrost isn’t enough
When the defrost cycle can’t keep up with the buildup of ice, it often points to a technical or installation issue. At that point, the frost is no longer just a weather reaction—it becomes a symptom of a problem that can reduce the unit’s performance, damage the fan, or block the coils.
Main Causes of Excessive Ice Build-Up on a Wall-Mounted Heat Pump
1. Poor drainage
At AirGreen, we’ve found one of the most frequent installation mistakes in Montréal and surrounding areas is the lack of a proper drainage system. When condensation can’t drain properly, it pools under the outdoor unit and continually freezes, forming a growing block of ice that restricts airflow.
2. Improper unit placement
Installing a wall-mounted heat pump too close to the ground or facing the prevailing wind can cause blown snow or ice to accumulate directly on the unit. In Laval and Longueuil, we’ve corrected multiple setups where the unit was placed less than 30 cm off the ground—making defrosting ineffective.
3. Lack of maintenance
Clogged filters, a dirty fan, or blocked coils can limit airflow and worsen frost formation. Regular HVAC maintenance is critical—especially before the deep freeze sets in. We recommend a full professional cleaning at least once a year.
4. A heat pump unsuited for Québec winters
Some lower-end models simply aren’t built to perform in temperatures of -20°C or below. In Terrebonne, we replaced a 12,000 BTU wall unit not certified ENERGY STAR with an 18,000 BTU Gree Extreme, equipped with intelligent defrost and engineered to function down to -30°C.
What We Actually Do at AirGreen to Fix Excessive Freezing
Case Study: January Service Call in Ahuntsic-Cartierville
A client contacted us after noticing a thick layer of ice under their FUJITSU KZAH 15,000 BTU wall-mounted heat pump, which had been installed by another contractor. The unit no longer defrosted and was blowing cold air indoors. After inspection, we identified:
-
The unit was installed just 20 cm above the ground.
-
Insufficient clearance on both sides.
-
No drainage trench at all.
-
The defrost cycle was misconfigured.
We raised the unit to 60 cm above the ground, installed a heated drain, reprogrammed the defrost cycle, and completed a full coil cleaning. The result: a fully functioning heat pump with no more freezing issues—even at -27°C.
Practical Tips to Avoid Ice Problems on Your Wall-Mounted Heat Pump
Optimal placement
-
The outdoor unit should be elevated (at least 45 to 60 cm from the ground).
-
Avoid installing it under a roof with no gutters (risk of icicles).
-
Ensure adequate side clearance (at least 30 cm on each side).
Preventive maintenance
-
Clean filters every 3 months.
-
Schedule annual inspections with an HVAC professional.
-
Check defrost function before winter begins.
Choosing the right heat pump for Québec winters
Go for models that are ENERGY STAR certified, like the Gree Extreme, Bosch BOVA, or FUJITSU KZAH, which are tested for extreme cold performance.
Why It’s Crucial to Hire Certified HVAC Experts
Having a high-performance wall-mounted heat pump is just the first step. It also needs to be installed and maintained by a team that understands the specific challenges of our climate. At AirGreen, we install every unit to exacting standards, taking into account the environment, building type, and prevailing wind direction. That’s why hundreds of clients across Montréal, Laval, Longueuil, the North Shore, and South Shore trust us year after year.
Key Takeaways
A wall-mounted heat pump freezing up in January isn’t necessarily defective—but it does need special attention. Placement, drainage, maintenance, and choosing the right model are the four essential pillars to avoid winter problems. AirGreen brings its expertise to your comfort all year round, with custom solutions and meticulous service across Greater Montréal.