A drop in performance you can’t see, but definitely feel: the hidden reasons behind a less efficient wall-mounted heat pump
In Montréal, Laval, Longueuil, the North Shore, and the South Shore, we regularly receive calls from customers wondering why their wall-mounted heat pump — though fairly new — seems to be working less efficiently than it did at first. Less warmth in the winter, weaker cooling in the summer, or even a sudden spike in electricity consumption.
This drop in efficiency isn’t inevitable, but it’s often tied to little-known factors. At AirGreen, we’ve identified the most common causes of this phenomenon — and more importantly, we know how to fix them for the long term.
What the symptoms reveal: subtle, but telling signs
The air feels lukewarm, cycles get longer, and comfort declines
A customer in Laval reached out to us after noticing that their Gree Lomo 23 wall-mounted heat pump | 18,000 BTU, installed just six months earlier, was no longer heating like it used to. Despite good home insulation, the indoor temperature struggled to reach 20 °C.
After an inspection, we found that the indoor filters were already clogged, cutting airflow by more than 35%. That simple buildup of dust had a direct impact on the overall system performance.
Higher energy bills without any change in behavior
In Longueuil, a family using a Fujitsu KZAH 15,000 BTU wall-mounted heat pump saw their electricity bill jump by 40%. Our analysis showed that the unit was running longer than necessary because of a poorly calibrated indoor temperature sensor.
The result: a slow but steady overconsumption that’s hard to detect without professional tools.
What are the most common causes?
Neglected maintenance: the silent enemy of heat pumps
Even a top-of-the-line unit installed correctly will quickly lose efficiency without regular maintenance. Dust, kitchen grease, pet hair… all accumulate and compromise:
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Airflow
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Heat exchange
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Proper fan operation
A professional cleaning once a year helps maintain the performance of your wall-mounted heat pump.
Improper settings or factory defaults left unchanged
Many installers don’t take the time to customize smart operating modes. The result: the heat pump runs on factory defaults, often unsuitable for our Quebec climate.
Common issues include:
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Heating mode activating at too high an outdoor temperature
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Auto mode misinterpreted (constant switching between heat/cool)
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Wrong defrost mode activated
At AirGreen, we tailor each setting to your home’s actual conditions.
An installation that doesn't match the real-world environment
In several cases across Montréal and the South Shore, we’ve corrected installations where airflow was blocked by furniture, curtains, or partitions. The air looped back on itself, distorting temperature readings and forcing the unit to run non-stop.
A simple repositioning or adjustment of the deflectors can instantly restore comfort.
The AirGreen method: thorough audit, precise correction, lasting results
Detailed technical inspection
When a client contacts us about a performance drop, we perform a comprehensive inspection:
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Heating or cooling cycle analysis
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Refrigerant pressure readings
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Temperature sensor checks
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Compressor and fan behavior monitoring
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Thermostat or remote control review
We use professional-grade diagnostic tools to detect issues that aren’t visible to the naked eye.
Real examples of AirGreen interventions
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In Saint-Eustache, a Bosch BOVA 24,000 BTU heat pump seemed to be underperforming. The real issue? The wall it was mounted on transmitted a vibration noise, triggering the unit’s silent mode without cause. Solution: installation of professional anti-vibration mounts.
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In Anjou, a Sharp ZU1 12,000 BTU unit entered defrost mode for over 20 minutes every hour. We discovered that the outdoor sensor was fully exposed to icy wind, throwing off its readings.
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In Saint-Bruno, a customer reported a noisy, underperforming system. Our team found that the R-32 refrigerant had been undercharged during installation, causing low compression. A calibrated recharge brought the system back to full performance.
How to prevent your wall-mounted heat pump from losing efficiency
Choose a certified, methodical, and local installer
A good installer doesn’t just mount the unit. They calibrate, test, adjust, and educate the client on proper system use. At AirGreen, every installation is documented and tested to the manufacturer’s standards.
Schedule full annual HVAC maintenance
We recommend a comprehensive annual maintenance visit, including:
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Filter and coil cleaning
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Drainage and duct inspection
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Pressure and temperature readings
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Settings update (winter/summer modes)
This service helps preserve your heat pump’s energy efficiency over time.
Watch for signs of performance loss
Don’t ignore the following symptoms:
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Air feels less hot or cold than before
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The unit runs longer
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Your bill goes up unexpectedly
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Unusual odors or sounds appear
Prompt intervention can prevent costly repairs.
Conclusion
Your wall-mounted heat pump was designed to deliver comfort and energy savings. But without proper maintenance, a precise installation, and regular monitoring, it can lose up to 30% of its efficiency within a year.
At AirGreen, we respond across Montréal, Laval, Longueuil, the North Shore, and the South Shore to ensure lasting performance, optimal comfort, and controlled energy bills. One call can make all the difference.