When indoor comfort lags behind: a common reality in Quebec homes
Many of you have noticed that in the middle of winter, your wall-mounted heat pump doesn’t heat as quickly as expected. Far from unusual, this phenomenon affects countless homes in Montreal, Laval, Longueuil, on the North Shore and the South Shore. At AirGreen, we’ve been called in to diagnose and fix this issue in dozens of installations. Here are the real technical reasons—sometimes unexpected—that explain this slow rise in temperature, and most importantly, how to resolve it effectively.
Understanding how a heat pump works in heating mode
First, let’s remember that a heat pump doesn’t produce heat, it captures it from the outdoor air and transfers it inside your home. Even when temperatures drop below freezing, high-performance models like the Gree Extreme or the Fujitsu KZAH R-32 can operate down to -30°C. But that doesn’t mean they’ll work at full power right when you turn them on.
Natural factors:
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Extremely low outdoor temperatures: the colder it is, the harder it is for the outdoor unit to extract enough heat.
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Defrost cycle: during deep cold, the heat pump switches into defrost mode to prevent ice buildup, temporarily pausing heating.
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Poor home insulation: even with a high-performance heat pump, weak insulation slows down heating.
Case study: Gree Extreme 18,000 BTU installed in Mascouche
We recently installed a Gree Extreme 18,000 BTU wall-mounted heat pump in a century-old house in Mascouche, with poorly insulated walls. In early January, the client noticed that it took more than 45 minutes for the main room to reach a comfortable temperature.
Our diagnosis:
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The unit was operating normally.
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The issue was the home’s high heat loss, combined with a poorly optimized thermostat setting.
AirGreen’s solution:
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We adjusted the setpoint temperature, added thermal insulation to certain walls, and scheduled a gradual pre-heating before the space was in use. The result: stable comfort, without needing to replace the unit.
Poor placement of the indoor unit: a common mistake
In several homes on the South Shore, we’ve seen units installed too close to the ceiling, pointing toward windows, or blocked by furniture.
Consequences:
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Warm air rises without effectively heating the living space.
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Temperature sensors pick up artificial heat, disrupting the heating cycle.
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The room feels like it’s heating slowly—or not at all.
AirGreen tip: always place the wall-mounted heat pump at the ideal height, on a central, unobstructed wall, allowing for unrestricted air distribution.
Improperly sized heat pump
A unit that’s underpowered in BTUs will never heat a space that’s too large efficiently. Conversely, an oversized unit in a small room will short-cycle, reducing its overall efficiency.
At AirGreen, we always perform a custom thermal analysis before any installation. For example, in Longueuil, a client had a competitor install a 9,000 BTU unit in a 600 sq. ft. living room. The result: slow heating, constant noise, and never-ending cycles.
We recommended a Midea25 12,000 BTU, properly matched to the space. Since installation, the client reports fast, quiet, and steady heating.
Common mistakes to avoid
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Turning off the heat pump completely at night: this forces an intense restart in the morning, consuming lots of energy.
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Programming large temperature swings between day and night.
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Using an electric space heater simultaneously, which confuses the heat pump’s sensors.
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Neglecting HVAC maintenance: clogged filters, dirty fans, or miscalibrated sensors can significantly slow heating.
Testimonials from AirGreen clients
“Since AirGreen adjusted our settings, our Gree Sapphire heats the house in 15 minutes—even at -20°C. A real difference.” — Julien, Laval
“We used to be cold every morning. AirGreen reviewed our programming and repositioned the Fujitsu: problem solved.” — Claire and Marc, Saint-Eustache
Why call AirGreen?
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On-site diagnostics, including heating performance analysis.
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Free adjustments for our existing clients, when applicable.
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Advice on optimizing your thermostat settings and home insulation.
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Professional HVAC maintenance, including filter cleaning, airflow checks, and sensor calibration.
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Local expertise on models suited to Montreal, Laval, Longueuil, North Shore, and South Shore conditions.
Conclusion: slow heating ≠ faulty unit
If your wall-mounted heat pump heats slowly in winter, it doesn’t necessarily mean it’s broken. In most cases, the culprit is poor configuration, bad placement, or a poorly insulated home. With help from a pro like AirGreen, you can restore fast, efficient, and energy-saving comfort.