At AirGreen, we’ve noticed a common mistake among many homeowners in Montréal, Laval, Longueuil, and on the North Shore and South Shore: a wall-mounted heat pump that’s the wrong size. Far too often, a unit is installed without any real analysis of the home’s thermal needs. The result? Discomfort, excessive electricity consumption, premature wear… and frustration. In this article, we’ll help you identify the 7 subtle but telling signs that your wall-mounted heat pump isn’t the right fit — and more importantly, how to fix it with professional care.
1. Your home stays cold in the winter… or too hot in the summer
This is one of the most obvious signs, but it’s often misunderstood. If your heat pump is constantly running without reaching the desired temperature, it’s most likely undersized. On the other hand, an oversized unit reaches the temperature too quickly and shuts off frequently, causing uncomfortable temperature swings.
2. The compressor keeps starting and stopping (short cycling)
This constant on/off behavior is the classic sign of an oversized heat pump. It causes:
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Premature wear on components.
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Increased energy consumption.
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Annoying operating noises.
3. High electricity bills despite owning a so-called energy-efficient model
Even a high-end wall-mounted heat pump, like the Fujitsu KZAH R-32 or the Gree Lomo, will consume more than it should if it’s not sized properly for the air volume in your space. A precise load calculation, done by an HVAC expert, is key to maximizing energy savings.
4. Some rooms are too hot while others stay cold
If your bedroom feels like a freezer while the living room is overheated, chances are the unit wasn’t selected based on each room’s specific characteristics: orientation, insulation, window size, ceiling height, and more.
At AirGreen, we recently solved this exact issue in a Longueuil condo where a poorly positioned 9,000 BTU wall-mounted heat pump wasn’t properly heating the main bedroom. We replaced it with a multi-zone setup using two correctly sized wall units, which permanently resolved the problem.
5. Loud unit or unusual vibrations
When a compressor is straining or running at full speed all the time, it can lead to:
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Vibrations transferring into the wall.
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Loud airflow or knocking sounds.
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Constant irritation in your living space.
These effects are often tied to a mismatch between the unit’s output and your home’s actual heating and cooling needs.
6. Frequent breakdowns or early component failure
An incorrectly sized unit operates outside of its optimal performance range. This leads to:
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Excess strain on the compressor.
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Overheating of electrical components.
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Shortened system lifespan.
In 2024, we replaced a 12,000 BTU heat pump installed in a Laval home where an 18,000 BTU unit was actually needed. The result: the compressor failed after only 3 years.
7. The unit seems to be working, but you’re never truly comfortable
Sometimes, everything looks “normal” from a technical standpoint… but the occupants just never feel quite right. This subtle but persistent discomfort often points to an improperly calculated heat load.
Why do so many sizing errors happen?
Properly sizing a wall-mounted heat pump depends on a wide range of factors:
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Room size and layout.
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Home orientation and sun exposure.
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Insulation quality and window type.
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Number of occupants.
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Heat from appliances and electronics.
Unfortunately, some companies install heat pumps “by eye” or just follow product spec sheets without doing a proper thermal analysis. At AirGreen, every installation starts with a detailed evaluation of your real-world needs, carried out by a certified technician.
How to fix an incorrectly sized installation
1. Have your system diagnosed by an HVAC specialist
Our team can come in to:
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Measure your unit’s actual performance.
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Evaluate your true heating and cooling requirements.
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Determine whether the system needs replacement or simply an adjustment.
2. Choose a properly sized, energy-efficient wall-mounted heat pump
We offer models that perform reliably even in extreme cold, such as:
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Gree Extreme 18,000 BTU, perfect for North Shore winters.
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Fujitsu KZAH R-32, efficient and ultra-quiet.
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Bosch BOVA/IDS Premium, silent and eligible for generous rebates.
3. Take advantage of available grants
By choosing an energy-efficient, correctly sized heat pump, you may qualify for incentives like:
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Hydro-Québec’s LogisVert: up to $2,500.
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Transition énergétique Québec: additional bonuses based on income and location.
These programs help offset the cost of a new or corrected professional installation.
Real examples of corrections made by AirGreen
Installation 1 – Montréal (Rosemont)
Problem: A 9,000 BTU heat pump installed in a 40 m² living room.
Symptoms: Insufficient winter heating, constant noise, discomfort.
Solution: Replaced with a Gree Extreme 12,000 BTU with better airflow and repositioned install. Result: optimal comfort, 18% energy savings.
Installation 2 – South Shore (Boucherville)
Problem: An oversized 18,000 BTU heat pump installed in a small condo.
Symptoms: Short cycles, lingering humidity, frequent breakdowns.
Solution: Replaced with a Fujitsu KZAH 9,000 BTU, recalibrated to fit the actual area. Result: peace and quiet, stable temps, and better humidity control.
Why trust AirGreen to fix a sizing error?
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Local expertise: optimized installations across Montréal, Laval, Longueuil, North Shore, and South Shore.
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Custom thermal evaluations.
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TEQ and RBQ certified technicians.
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Support with grant applications.
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Commitment to long-term comfort.
Your comfort deserves more than guesswork.
A good unit that’s the wrong size is still the wrong unit. At AirGreen, we believe that a perfectly tailored installation is the only way to guarantee comfort, savings, and long-term durability.
Contact us today for a free diagnosis of your current setup.