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Rive-Sud : la thermopompe centrale installée dans un garage mal ventilé — autopsie d’un échec
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South Shore: The Central Heat Pump Installed in a Poorly Ventilated Garage — Autopsy of a Failure

When Poor Planning Turns an HVAC Project Into an Avoidable Nightmare

Even the best equipment can’t make up for a bad HVAC installation plan. That’s a lesson we’ve learned through many corrective interventions, including one telling case on the South Shore, where we were called in to fix a clear-cut example: a central heat pump installed inside a closed garage with no proper ventilation, which led to a chain reaction of technical issues, energy overconsumption, and completely avoidable customer dissatisfaction.

In this article, we break down this failed installation — not done by AirGreen — to highlight the mistakes to avoid, while sharing our professional recommendations to ensure your HVAC system runs as it should.

Installation Context: A Poorly Supervised Project from the Start

This homeowner in Saint-Jean-sur-Richelieu wanted to replace an old electric heating system with a Lennox ML14XP1 central heat pump, paired with a 15 kW backup electric furnace. The system was meant to serve a single-story house with an attached garage.

Unfortunately, the original contractor:

  • Installed the outdoor unit inside the garage, assuming it would be protected from the cold and vandalism

  • Didn’t provide any venting or mechanical airflow

  • Failed to inform the customer about the risks of heat build-up, humidity, or performance loss

The result: the heat pump underperformed, overheated in summer, and froze in winter. Meanwhile, the Hydro-Québec bill kept rising.

Direct Consequences of a Bad Installation in a Closed Garage

1. Overheating of the outdoor unit in summer
With no access to fresh air, the unit couldn’t release the heat absorbed from inside the house. Pressure built up, cycles shortened, and the compressor started wearing out prematurely.

2. Humidity build-up and accelerated corrosion
Stale air in an enclosed garage creates a humid microclimate that damages electronic circuits, electrical connections, and coil fins.

3. Heating failure in winter
A heat pump needs outdoor air to heat efficiently. In a sealed garage, the temperature dropped too low, causing the electric furnace to run almost non-stop, wiping out any energy savings.

4. Voided warranty
Manufacturers require compliant installations to honor warranties. Since this unit was installed in an unsuitable location, repairs were not covered.

AirGreen’s Intervention: Audit, Diagnostics, and a Long-Term Solution

The client contacted us after 9 months of discomfort and excessive costs. Our technical team performed a full diagnostic, identifying several critical points:

  • Garage interior temperatures reaching 46°C in July

  • Constant humidity levels over 70%

  • System performance 35% below expected efficiency

Our Concrete Recommendations:

  1. Relocate the outdoor unit to the backyard on an elevated base with frost protection

  2. Add a snow guard and anti-icing roof for winter use

  3. Rework all wiring and ducting

  4. Deep clean all components exposed to corrosion

Once everything was corrected, system performance improved immediately, and energy consumption dropped by 28% the very next month.

Key Lessons from this HVAC Installation Failure

Always follow manufacturer installation guidelines

A central heat pump must always be placed:

  • Outside, in a well-ventilated area

  • At least 12 to 24 inches from the wall

  • On a stable slab or anti-vibration base

  • Protected from debris, snow, and excess moisture

Evaluate every building’s unique needs

At AirGreen, every project starts with a personalized thermal analysis, taking into account:

  • Building orientation

  • Shade or sun exposure

  • Room and wall layout

  • Actual heating/cooling demands

Keep the client informed at every stage

An informed client is a satisfied client. We always explain the technical reasoning behind our choices, available alternatives, and system limitations.

Why Trust AirGreen for a Successful Installation?

  • No subcontracting: our technicians are trained in-house

  • Certified specialists for Lennox, Bosch, Gree, Fujitsu

  • Over 1,000 completed projects in Montréal, Laval, Longueuil, North Shore and South Shore

  • Support for LogisVert grants

  • Fast, well-documented after-sales service

Planning to install a central heat pump on the South Shore or anywhere in Québec?
Avoid costly mistakes. Trust AirGreen, your expert in smart, code-compliant HVAC installation, and enjoy optimal comfort all year round.