Technical analysis and common mistakes behind underperforming HVAC systems
At AirGreen, we regularly receive calls from clients who, despite installing a brand-new central heat pump, still feel cold inside their home, especially during the winter months. The unit is brand new, often from reputable brands like Lennox, Bosch, or Gree, with excellent seasonal efficiency ratings on paper.
So why are some homes still cold, even with the latest central heat pump technology? Here are the real reasons, based on actual service calls we’ve completed across Montréal, Laval, Longueuil, the North Shore, and the South Shore.
1. The heat pump is improperly sized
This is the most common issue we find during inspections. A heat pump that’s too small simply won’t have enough capacity to heat the space during deep freezes. One that’s too large will short-cycle, which hurts both comfort and energy efficiency.
Case from Laval:
An 1,800 sq. ft. home had been outfitted with a Bosch BOVA 3-ton central heat pump. While powerful on paper, it was undersized for the actual thermal load at -25 °C. The result: indoor temperatures stalled around 18 °C.
Our recommendations:
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Always perform a proper heat load calculation (Manual J) before selecting a model
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Never rely solely on square footage
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Consider sun exposure, materials, windows, and air leaks
2. Undersized, leaky, or dirty ductwork
Even the best heat pump on the market will underperform if the warm air doesn’t circulate properly. Ducts that are too narrow, poorly designed, or inadequately insulated can cause 20 to 40% heat loss, leaving some parts of your home cold no matter how hard the system works.
Example in Longueuil:
A recent install of a Lennox EL18XPV central heat pump wasn’t properly heating the main floor living room. We discovered that 30% of the warm air was leaking into an unsealed crawlspace.
What AirGreen always does:
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Check the condition and insulation of the existing ducts
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Seal all leaks using aluminum tape and mastic
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Fully clean the duct network when necessary
3. The system is being used improperly
Some user habits can cancel out the efficiency gains of a new central heat pump. Lowering the thermostat drastically during the day and then cranking it up at night overloads the system. Closing vents or blocking them with furniture also prevents even heat distribution.
Practical tips:
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Maintain a stable temperature (maximum 2 °C difference between day and night)
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Keep all vents open to ensure proper airflow
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Use a smart thermostat or program your system thoughtfully
4. The thermostat is misconfigured or incompatible
A poorly set or incompatible thermostat can make even the best heat pump ineffective. If the thermostat doesn’t recognize the type of system installed (heat pump with auxiliary heat, inverter technology, etc.), it may trigger the backup heat too often—or fail to defrost at the right times.
Case in Saint-Eustache:
A client with a Gree Flexx 48,000 BTU unit noticed their bill skyrocketing. Upon inspection, we found that the "heat pump" setting wasn’t activated, and the 15 kW backup heat was running constantly.
AirGreen solutions:
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Verify thermostat compatibility with the heat pump
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Fully reprogram the system at startup
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Provide quick training for the client on how to maintain proper settings
5. The house has poor insulation or thermal bridges
Sometimes, the problem lies not with the heat pump or the installation, but with the home’s building envelope. Drafts, poorly insulated walls, leaky ceilings, or outdated windows make heating a challenge—even with a high-performance HVAC system.
Observation in Montréal (Rosemont):
A semi-detached home with a Fujitsu Airstage central heat pump couldn’t reach 21 °C in the upstairs bedrooms. A thermal scan revealed several cold spots in the north-facing walls and the stairwell ceiling.
Our recommendations:
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Have a thermal imaging inspection performed on your home
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Add insulation to critical areas (attic, basement, exterior walls)
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Seal all openings: windows, doors, electrical outlets
AirGreen helps you unlock your central heat pump’s full potential
A new central heat pump can be a fantastic investment—if it’s properly installed, properly used, and part of a well-insulated home.
At AirGreen, we don’t just install a system. We guide you through the complete optimization of your comfort and energy efficiency, thanks to:
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In-depth technical diagnostics (sizing, ductwork, insulation)
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Customized settings to get the most from your system
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Field-proven expertise throughout Montréal, Laval, Longueuil, the North Shore, and the South Shore
If your house still feels cold despite a recent central heat pump, contact our team. Together, we’ll pinpoint the cause and fix it—so your HVAC investment truly pays off, even in Québec’s coldest winter days.