A Performance Drop: Understanding Why Efficiency Declines
At AirGreen, we often hear the same question from clients in Montréal, Laval, Longueuil, the North Shore, and the South Shore: “My wall-mounted heat pump doesn’t heat like it used to, even though it was well installed. Why?” This situation can be frustrating, especially when the initial investment was significant and the system worked well at first. Let’s take a look at the real reasons behind a drop in efficiency, even when the installation was done correctly.
HVAC Maintenance Often Overlooked: The #1 Factor
One of the main reasons for performance loss is lack of regular maintenance. A wall-mounted heat pump — no matter how efficient, whether it’s a Fujitsu KZAH 12,000 BTU, Gree Extreme 18,000 BTU, or a SHARP ZU1 24,000 BTU — will build up dirt, dust, and pollutants that block:
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The indoor filter: when it’s clogged, it restricts airflow.
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The heat exchanger: if covered in dust, it transfers heat less effectively.
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The condensate drain: a blocked drain causes excess humidity and unpleasant odors.
Without annual professional cleaning, energy efficiency can drop by 15 to 30% as early as the second year. At AirGreen, we offer complete HVAC maintenance contracts across Greater Montréal to help prevent these performance issues.
A Heat Pump Poorly Suited to the Home’s Thermal Reality
Even if the original installation was done properly, it may no longer match your current needs. Here are a few scenarios we frequently encounter:
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Changes in insulation (finishing or removing a basement, renovations).
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New room configurations (open concept layouts, removed walls).
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Increased living space without resizing the unit.
For example, a Gree Lomo 12,000 BTU wall-mounted heat pump installed in a condo in 2020 may become inadequate if a mezzanine was added since then. Our qualified technicians always perform a thermal load calculation when a client reports loss of efficiency to confirm whether the unit is still appropriately sized.
Everyday Misuse
Another often underestimated factor is improper usage settings. Even the best wall-mounted heat pump can lose efficiency if:
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The AUTO mode is constantly used, causing the system to switch back and forth between heating and cooling.
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The thermostat is poorly placed (near a heat source or in a draft).
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The user opens windows while the system is running.
We recently assisted a client in Longueuil whose Fujitsu KZAH 15,000 BTU model seemed underperforming. In reality, heavy curtains blocked airflow from the indoor unit. A simple adjustment restored comfort without touching the unit itself.
Quality HVAC Installations Need Long-Term Follow-Up
What We’ve Observed in the Field
At AirGreen, we’ve installed hundreds of wall-mounted heat pumps in Montréal and surrounding areas. Our field experience allows us to quickly pinpoint underperformance issues. Here are some real-life examples from our work:
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In Boisbriand, a MIDEA25 9,000 BTU wall-mounted heat pump installed in 2022 stopped heating efficiently by 2025. The client had skipped maintenance entirely, and the drain was completely clogged with mold.
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In Verdun, a dual-zone Sharp ZU1 18,000 + 9,000 BTU system underperformed in the main bedroom. The issue was a low refrigerant level due to a loose connection in the 9,000 BTU head. Once fixed, performance was fully restored.
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In Boucherville, we replaced a Gree unit with a Fujitsu KZAH 12,000 BTU wall-mounted heat pump perfectly suited for a newly renovated space. The result: improved efficiency and a 20% drop in energy consumption.
Indoor Air Quality: A Hidden Impact
A wall-mounted heat pump also acts as a secondary air purifier. If indoor air is laden with fine particles, pet hair, or excess humidity, it impacts:
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The blower motor, which has to work harder.
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The temperature sensors’ accuracy.
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Premature wear on components.
In these situations, we recommend a complete high-pressure cleaning of the indoor unit every 2 to 3 years.
How AirGreen Restores the Efficiency of Your Wall-Mounted Heat Pump
Complete Technical Diagnosis
Our teams offer a comprehensive inspection service, including:
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Reading pressure parameters.
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Checking the electronic control board.
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Evaluating the seasonal performance ratings (SEER/HSPF).
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Inspecting the refrigerant lines, especially in newer systems using R-32 or R-454B.
Smart Replacement or Adjustment
We always propose a solution tailored to your situation:
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Deep HVAC cleaning.
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Adding a second unit to cover new living spaces.
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Replacing the indoor unit if outdated or undersized.
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Adjusting electrical wiring or drainage as needed.
Assistance with LogisVert Grants
In many cases, Hydro-Québec grants can cover the cost of replacing a system deemed inefficient. For example, a Sharp ZU1 18,000 BTU wall-mounted heat pump may qualify for a $1,704 rebate, if the replacement leads to measurable energy gains.
The Key Takeaway
A proper installation isn’t enough to guarantee long-term performance. The efficiency of a wall-mounted heat pump depends on the right equipment, correct use, regular maintenance, and adapting to changes in your home.
At AirGreen, we serve the entire Montréal region, including Laval, Longueuil, the North Shore, and the South Shore to diagnose, correct, and optimize your wall-mounted systems. Whether it’s a new installation or scheduled maintenance, our field expertise makes all the difference.