Understanding why your wall-mounted heat pump seems less effective when it’s extremely cold outside
At AirGreen, we frequently receive calls from concerned clients in Montréal, Laval, Longueuil, the North Shore and South Shore, saying that their wall-mounted heat pump is blowing cold air during freezing weather, often in the heart of January or February. This phenomenon can feel counterintuitive, especially if you're relying on your system to keep your home comfortable. Fortunately, this behaviour doesn’t always mean something is broken. In this article, we’ll explain in detail why this happens, how to tell the difference between normal operation and a real issue, and most importantly, the exact solutions we provide during our service calls.
How does a wall-mounted heat pump work in winter?
A wall-mounted heat pump works on the principle of heat transfer. In heating mode, it captures heat from the outside air — even when it’s cold — and transfers it into your home. Thanks to modern technology, models like the FUJITSU KZAH R-32, Gree Extreme, or Sharp ZU1 can heat efficiently down to -25°C.
However, when the temperature drops below -20°C, certain units enter specific operating phases that may make it feel like they’re “blowing cold air.”
The main reasons why your heat pump may be blowing cold air
1. Automatic defrost cycle
When it’s very cold, frost can form on the outdoor unit. To maintain its performance, the heat pump automatically enters a defrost mode. During this cycle (which usually lasts 5 to 15 minutes), the system temporarily reverses its operation to warm up the outdoor unit, which results in a cooler airflow indoors. This behaviour is completely normal and built into the system by the manufacturer.
2. Reduced heat output in extreme cold
Even top-tier models lose some heating power when outdoor temperatures drop below -20°C. For example, an 18,000 BTU heat pump, which normally heats an entire living space, may struggle to keep up with the heavy heat losses if insulation is poor.
3. Dirty filter or evaporator
During many of our visits — especially in areas like Anjou, Brossard, or Sainte-Julie — we’ve noticed that clogged filters or a dirty heat exchanger drastically reduce heating output. This can create the sensation of cold air blowing, even when the unit is trying to heat.
4. Improper sizing of the unit
One common mistake when purchasing or installing through non-specialists is incorrect sizing. A unit that’s too small won’t deliver enough heat in freezing conditions. That’s why, at AirGreen, we always perform a full thermal assessment before every installation.
How to tell the difference between normal operation and a real malfunction?
It’s important to distinguish between:
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Brief cool or lukewarm air blowing (due to defrost): normal.
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Continuous cold air that doesn’t return to warm: potentially a problem.
Here are a few red flags to look for:
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The air blowing remains cold constantly.
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The outdoor unit doesn’t seem to be running.
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You hear unusual sounds (clicking, excessive vibration).
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Electricity usage spikes, but the indoor temperature doesn’t increase.
Real-world case studies from our clients
Installation in Laval: FUJITSU KZAH R-32 – 18,000 BTU
A client contacted us in January during a cold snap. Her wall-mounted heat pump was blowing cold air in the evening, making the living room uncomfortable. Our team quickly discovered that the defrost cycle was triggering too frequently due to poor placement of the outdoor unit with inadequate ventilation. We reinstalled the unit at an optimized height and cleaned the ducts. Result: comfort restored, even at -24°C.
Service call in Longueuil: Gree Extreme 24,000 BTU
A multi-residential building reported declining heating performance during extreme cold. On site, our technician discovered that the filters hadn’t been cleaned in over 12 months. After a full maintenance and activation of the high-performance mode, the heat pump regained its original efficiency.
Our advice to prevent this issue
✔ Schedule regular HVAC maintenance
We recommend a full annual cleaning of your wall units. This includes cleaning filters, the heat exchanger, and the outdoor unit. At AirGreen, we offer seasonal maintenance packages tailored to Québec’s climate.
✔ Check your insulation
Poor insulation increases heat loss and overworks your heat pump. In extreme cold, this can cause the sensation of cold air blowing.
✔ Choose a unit designed for our climate
Some models are specifically built for Québec winters. For example, the Gree Sapphire wall-mounted heat pump maintains stable heating capacity down to -30°C. At AirGreen, we guide you toward the most efficient models eligible for Hydro-Québec’s LogisVert grants.
What to do if your heat pump is blowing cold air today?
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Check the airflow by hand: is it lukewarm or truly cold?
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Observe the defrost cycle frequency: is it occurring every 20 minutes?
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Inspect the filters: are they clean?
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Call our HVAC specialists: we respond quickly across Montréal, Laval, Longueuil, the North Shore, and South Shore.
Why choose AirGreen to service or repair your wall-mounted heat pump?
We’re much more than just an installer. At AirGreen, we combine accurate diagnostics, certified technicians, genuine replacement parts, and advice tailored to the Québec climate. Every service call is personalized: we analyze your property’s specific conditions, your usage habits, and your system’s actual performance.
Our reputation is built on solid installations, thorough preventative maintenance, and long-term solutions — even in the harshest winters.