A growing issue during Montréal’s increasingly hot summers
Every summer, as heat waves hit Montréal, Laval, Longueuil, the North Shore and the South Shore, AirGreen receives more and more calls from clients frustrated with the performance of their wall-mounted heat pump. Despite owning recent and well-maintained systems, some units struggle to maintain a consistently cool temperature inside the home, especially during the hottest days when the mercury rises above 32°C.
Why do these performance failures happen? And more importantly, how can you avoid them right from installation? Drawing from our experience across hundreds of HVAC projects in Greater Montréal, we’ve identified the main causes and developed the right solutions.
Why do some wall-mounted heat pumps underperform during heat waves?
1. Undersized BTU from the start
This is the most common mistake. When a 9,000 BTU unit is installed in a 1,000 sq. ft. home with large south-facing windows, it will never be able to meet the cooling demand during a heat wave. At AirGreen, we always perform a precise thermal load calculation, factoring in square footage, orientation, insulation, and daily room usage.
2. Entry-level models not built for peak heat performance
Some budget models simply aren’t designed to deliver stable performance at extreme temperatures. We’ve observed that many wall-mounted heat pumps lose up to 30% of their cooling capacity above 30°C, especially if they use a single-stage compressor instead of an inverter. Clients who opt for these cheap systems end up paying in discomfort.
3. Poor indoor air circulation
Even with a high-performance heat pump, if the wall unit is poorly positioned, cool air won’t circulate properly. This creates hot zones, especially upstairs or in distant rooms. Our teams ensure strategic installation: unit height, clearance, airflow, and natural air movement are always considered.
4. Lack of regular HVAC maintenance
Clogged filters or a blocked heat exchanger drastically reduce system efficiency. During a heat wave, these oversights lead to loss of power and units running nonstop without ever reaching the set temperature.
Real-life examples from AirGreen installations in Montréal and the South Shore
Case #1 – Pointe-aux-Trembles: undersized unit in a corner condo
A client contacted us after two frustrating summers: his 12,000 BTU wall-mounted heat pump installed in a 1,200 sq. ft. condo couldn’t lower the temperature below 26°C during a heat wave. After inspection, we found the unit was underdimensioned and the ceiling had poor insulation.
Solution: replacement with a Gree Extreme 18,000 BTU unit, featuring SEER 25.3, smart control, and optimized installation. Result: stable temperature of 22°C even on days reaching 34°C.
Case #2 – Brossard: poor wall unit orientation
In a two-story home, the wall unit was installed facing a wall with no way to push cool air toward the staircase. Result: persistent hot zones in the upstairs bedrooms. Our technicians recommended relocating the unit and adding an air transfer fan.
How AirGreen optimizes installations for extreme heat conditions
Heat pumps designed to perform even at 40°C
We install models built to operate consistently even in very high outdoor temperatures, including:
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Fujitsu KZAH 12,000 BTU R-32 – Excellent energy performance, SEER 26.5
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Gree Sapphire 18,000 BTU – High-efficiency inverter compressor, ultra-quiet
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LG Prestige 12,000 BTU – Dual Inverter technology, built-in Wi-Fi, steady performance
A precise thermal study before every project
We analyze your real BTU requirements, room by room. A cathedral-style living room doesn’t have the same needs as a closed home office. Our team tailors every quote so that the chosen wall-mounted heat pump meets the actual demands of the home.
Recommended HVAC maintenance twice a year during heat wave season
Heat waves place a heavy burden on your system. We offer HVAC maintenance contracts that include:
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Filter and heat exchanger cleaning
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Airflow and refrigerant level checks
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Drainage line inspection
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Preventive performance diagnostics
Practical tips for optimal comfort during heat waves
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Never undersize your heat pump to save money upfront: long-term comfort has a cost.
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Choose a model with a high SEER, certified for high outdoor temperatures.
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Ensure professional HVAC installation, with proper indoor unit placement.
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Consider adding a fan or supplemental mini-split in large or multi-level homes.
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Schedule regular maintenance starting in spring, before the heat arrives.
Conclusion: Choosing the right wall-mounted heat pump means preparing for future summers
Heat waves are becoming more common in Montréal. To ensure consistent indoor comfort, your heat pump choice, installation, and maintenance must be done with care and precision.
At AirGreen, we support our clients every step of the way with durable installations, adapted to Québec’s climate reality, and designed to last over 10 years. For cool, worry-free summers, trust in our expertise.