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Is Your Wall-Mounted Heat Pump Struggling Due to Poor Home Insulation? A 4-Point Diagnostic

A high-performance wall-mounted heat pump—but ineffective in a poorly insulated home?

At AirGreen, we regularly meet clients in Montréal, Laval, Longueuil, on the North Shore and South Shore who complain that their wall-mounted heat pump isn’t delivering the comfort they expected—even when it’s brand-new, properly sized, and from a reputable brand. In many cases, the issue doesn’t come from the unit itself, but from a factor that’s too often overlooked: your home’s thermal insulation.

Before questioning the efficiency of your HVAC system or calling for a service visit, it’s essential to analyze the environment it operates in. A poorly insulated home acts like a heat drain in winter and an oven in summer, making your heat pump work harder—and often without real results.

1. Rooms stay cold even when heating? Your walls or windows might be the problem

A frequent complaint we hear during our service calls across Greater Montréal is that of cold spots that never go away, even when the HVAC system is running at full capacity.

Our technicians often identify the following culprits:

  • Single-pane windows or poorly sealed frames

  • Exterior walls with little or no insulation

  • Drafts near baseboards or window frames

  • Major thermal bridges at corners and joints

In a Laval home, we were recently asked to inspect a 12,000 BTU FUJITSU KZAH heat pump installed just a year earlier. The unit was working perfectly, yet the main room never reached more than 19°C in the winter. After a full inspection, we discovered the walls were practically uninsulated, leading to significant heat loss. The issue wasn’t the heat pump—it was the building envelope.

2. Unexplained energy overuse? Your attic or basement insulation may be the cause

Even the best Inverter wall-mounted heat pumps—such as Gree Lomo, Sharp ZU1 or Midea models—can’t compensate for massive heat loss from an uninsulated attic or crawlspace.

We advise our clients to check the following:

  • Insulation thickness and type in the attic (minimum R-41 recommended in Quebec)

  • Signs of moisture or mold, indicators of poor insulation

  • Air infiltration through access hatches or ducts

  • Lack of rigid insulation on basement walls or improperly installed vapor barriers

In Longueuil, a client reached out to us because their winter electricity bill had doubled since installing a MIDEA25 wall-mounted heat pump. The verdict: an attic barely insulated with old mineral wool from the 1980s. After re-insulating the space, consumption dropped by 28% the following month.

3. Your heat pump blows warm or cool air... but with little effect? Your home’s air tightness may be the issue

A wall-mounted heat pump’s performance doesn’t rely solely on BTU output or SEER/HSPF ratings. Poor air sealing makes any HVAC system less effective, because the conditioned air escapes as quickly as it’s produced.

Critical points to inspect:

  • Exterior door seals (often missing or deteriorated)

  • Cracks in the foundation or around window frames

  • Unsealed access hatches

  • Leaky or uninsulated exhaust ducts

At AirGreen, we recommend all clients invest in a blower door test before installing or replacing any HVAC system. This simple procedure helps quantify air leakage and build a targeted improvement plan.

4. Premature wear on your unit? Insulation also impacts lifespan

A heat pump running constantly to compensate for ongoing heat loss wears out faster—even if it’s a top-tier, new-generation model.

Common signs:

  • Compressor short-cycling

  • Filters and coils getting dirty more often than expected

  • Frequent indoor temperature swings

  • Premature failure of electronic boards

At a North Shore residence, we had to replace a Sharp ZU1 compressor after just three winters. The cause? Poor insulation combined with an undersized unit. We helped the client improve the insulation, then installed a better-suited system. Since then—not a single issue.

Conclusion: insulation—an invisible but critical foundation of any good HVAC system

At AirGreen, we believe a wall-mounted heat pump replacement project should never be approached in isolation. It should be part of a comprehensive energy performance plan, one that considers:

  • The analysis of the building envelope’s thermal condition

  • The precise sizing of the heat pump

  • A match between system capacity and actual needs

  • Optimization of air tightness and circulation

Our recommendations before any wall-mounted heat pump installation:

  1. Get a full thermal assessment of your home

  2. Fix insulation weaknesses first

  3. Choose an Inverter model that fits your space

  4. Trust the installation to an experienced team like AirGreen

We operate daily in Montréal, Laval, Longueuil, the North Shore and the South Shore, with expert insight that goes beyond the equipment. With this holistic approach, we deliver HVAC installations that last longer, use less energy, and provide superior comfort.

Unsure where your heating or cooling problems are coming from? Contact us. A simple diagnostic could completely transform your system’s efficiency.

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