Summer in Québec may be short, but when heatwaves hit Montréal, Laval, Longueuil, the North Shore or South Shore, they spare no one. And while air conditioning becomes an essential ally, a power outage at the height of a heatwave can turn comfort into a real nightmare. At AirGreen, we understand how critical it is to have a reliable HVAC (heating, ventilation and air conditioning) system during these moments. One question comes up again and again: can a wall-mounted air conditioner run on a generator in an emergency? Let’s explore the answers, best practices, and the custom solutions we offer at AirGreen to ensure your comfort even when the power grid fails.
Why are summer power outages becoming more frequent?
In Québec, rising heatwaves are causing electrical grid overloads, especially in highly air-conditioned regions like Montréal or the South Shore. Air conditioners run at full capacity, leading to a sudden surge in energy demand. The result: localized power outages or temporary shutdowns to ease the strain on the grid.
In this context, having a reliable backup solution such as a generator becomes a strategic move to keep your wall-mounted air conditioner running.
Wall-mounted AC and generator: compatibility to be carefully evaluated
Not all wall-mounted air conditioners are the same
At AirGreen, we frequently install high-performance, energy-efficient wall-mounted air conditioners from brands like Gree, Sharp, Fujitsu, or Mitsubishi. These units come in various capacities (from 9,000 to 24,000 BTU) and feature advanced inverter technology. But to run on a generator, several factors must be considered:
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Startup wattage (peak watts): some air conditioners require a temporarily higher wattage to start.
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Inverter technology: more flexible in consumption, but requires stable voltage.
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Electrical compatibility: 120V or 240V? Single-phase or three-phase? This is critical when choosing a generator.
Real example: Installation of a Gree Lomo 12,000 BTU in Laval
We recently installed a Gree Lomo 12,000 BTU wall-mounted air conditioner in a home in Laval. The homeowner, concerned about potential outages, asked for a complete assessment to see if it could run on a generator. Based on our analysis, we recommended a 3,000 W inverter gas generator, stable enough to support both the startup and continuous operation of the unit. We also installed a manual transfer switch for seamless alternative power connection.
Choosing the right generator for your wall-mounted air conditioner
Calculating the required power
A 9,000 to 12,000 BTU wall-mounted AC unit generally requires between 1,000 and 1,800 watts while running, but can demand up to 2,500 watts at startup.
A larger 18,000 to 24,000 BTU model may use up to 3,500 watts at peak. It’s important to plan a safety margin for startup surges.
Generator types recommended by AirGreen
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3,000 W inverter gas generator (e.g., Honda EU3000iS): quiet, compact, ideal for a unit up to 12,000 BTU.
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5,000 W or higher gas generator: suitable for multiple units or 18,000 BTU+ models.
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Dual fuel propane/gas option: very practical for secondary homes or rural zones.
Safe installation: AirGreen’s recommendations
We strongly advise against makeshift connections during outages. A safe and code-compliant installation is essential to avoid electric shock risks or equipment damage.
Our certified electrician partners can install a manual or automatic transfer switch, allowing your wall-mounted AC unit to be powered quickly and safely, without any risk of backfeeding into the Hydro-Québec grid.
Case study: Home in Longueuil – Fujitsu KZAS 18,000 BTU AC unit
In this family home, we installed a Fujitsu KZAS 18,000 BTU wall-mounted unit, known for its energy efficiency. To secure their comfort during outages, the clients opted for a 6,500 W automatic-start propane generator. The result: a fully autonomous and reliable system, even during extended blackouts.
Our recommendations for an effective emergency HVAC system
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Have the real power demand evaluated by a professional.
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Choose an inverter generator for voltage stability, essential for inverter AC units.
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Plan for annual generator maintenance to ensure it’s ready when needed.
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Consider a small UPS (battery backup) to protect the sensitive electronics of modern models.
Why choose AirGreen?
At AirGreen, we do more than install wall-mounted air conditioners in Montréal, Laval, Longueuil, or the North and South Shores. We offer complete, smart, and customized solutions. When a customer asks about running their HVAC system on a generator, we respond with precision:
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Technical evaluation of the installed unit (BTU, consumption, voltage).
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Calculation of energy needs and tailored recommendations.
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Coordination with a certified electrician for safe generator installation.
We’ve helped dozens of households in the region secure their thermal comfort during outages, while ensuring equipment longevity.
Common mistakes to avoid
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Choosing a generator too weak for the load.
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Failing to include surge protection.
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Connecting the unit without a transfer switch: dangerous for both your equipment and Hydro-Québec technicians.
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Letting the generator sit unused for long periods without regular testing.
Conclusion: yes, but under the right conditions
Yes, a wall-mounted air conditioner can run on a generator, but only if certain technical and safety criteria are met. It’s not as simple as plugging in the device — it requires a thorough assessment, especially for modern inverter models that demand a stable voltage.
At AirGreen, we understand these issues inside and out. We help you choose the right generator, prepare your HVAC installation for any situation, and protect your comfort, even when the power grid fails.