These common air conditioning mistakes cost you comfort, efficiency… and a higher electricity bill
Every year, thousands of homeowners and businesses in Montréal, Laval, Longueuil, on the North Shore and South Shore invest in air conditioning to improve comfort or optimize indoor environments. Yet even with the best intentions, over 90% of users still make at least one major mistake when it comes to their cooling systems. At AirGreen, we’re frequently called in to fix these missteps—often too late, after the system’s efficiency has dropped and the issues are already affecting daily life. Here are the 7 most common mistakes to avoid in 2025, along with the real-life solutions we implement every day in the field.
1. Choosing an incorrectly sized heat pump or wall-mounted AC unit
Getting the sizing wrong is one of the most expensive long-term errors. An oversized unit wastes energy, short-cycles (which wears down the compressor faster), and poorly manages humidity. An undersized unit struggles constantly to reach the set temperature, running non-stop and still leaving you uncomfortable.
At AirGreen, we perform a complete thermal analysis of the space before every HVAC installation, factoring in sun exposure, insulation, number of occupants, and square footage. For instance, during a recent install in Chambly, a client initially requested a 12,000 BTU model. But our analysis showed that an 18,000 BTU Gree Extreme was a much better match for his 80 m² home with cathedral ceilings.
2. Neglecting regular HVAC maintenance
A poorly maintained system can lose up to 30% of its efficiency within just a few years. We often encounter systems with clogged filters, blocked drains, or grimy evaporator coils. This doesn’t just reduce performance—it significantly raises the risk of breakdowns.
At AirGreen, we offer customized HVAC maintenance plans that include deep cleaning, pressure checks, temperature readings, and fine-tuning of system settings. In 2024 in Sainte-Thérèse, a routine maintenance call helped a customer avoid a major system failure just days before a heatwave hit.
3. Installing the unit in the wrong location
Where you install your indoor and outdoor units has a huge impact on performance. Too often, indoor units are blocked by curtains, furniture, or staircases, and outdoor units are crammed into tight spots, too close to walls, or directly exposed to sunlight.
Our certified technicians always ensure strategic placement. In Longueuil, we recently moved an outdoor unit just 60 cm for better airflow. This small adjustment reduced exhaust air temperature by 4°C and significantly improved system performance.
4. Thinking HVAC is only for summer use
A common misconception: seeing wall-mounted air conditioners as seasonal appliances. In reality, most modern wall-mounted heat pumps are reversible systems that work efficiently down to -30°C, like the Fujitsu KZAH R-32 or Bosch BIVA IDS Premium models.
We equipped a duplex in Laval with a 24,000 BTU Bosch heat pump in March 2024. The client heated his entire home with it until the end of winter without turning on the baseboards once—saving over $450 on his Hydro-Québec bill.
5. Focusing only on the purchase price without factoring in grants
Many Quebecers are still unaware that they can get significant government rebates thanks to Hydro-Québec’s LogisVert program. Depending on the unit model, size, and energy rating, you can qualify for up to $2,172 in rebates, as is the case with some Sharp ZU1 15,000 BTU models.
At AirGreen, we help each client navigate the paperwork to make the most of these grants. In Brossard, a client was initially leaning toward a budget model. But after calculating the rebates, he was able to afford a top-tier 24,000 BTU Gree Extreme—without going over budget.
6. Trying to install the HVAC system yourself
Some people try to save a few hundred dollars by attempting a DIY install. This often leads to refrigerant leaks, faulty electrical connections, and even fire hazards due to overloading.
Our teams, fully certified and experienced, follow all Quebec safety and electrical codes. We recently had to redo a full botched installation in Terrebonne, where a misaligned condensate line caused water damage on a newly finished wall.
7. Forgetting to assess insulation and ventilation
Even the best HVAC system can’t make up for poor insulation or inefficient ventilation. This leads to energy loss and constant discomfort.
Before every project, our experts conduct a full building assessment. In Saint-Lambert, we advised a client to add R-24 insulation in the attic before installing his heat pump. The result: less strain on the system, stable indoor temperatures, and a 25% reduction in energy bills.
How to avoid these mistakes with AirGreen
At AirGreen, we believe that a great air conditioning system starts with attentive listening, a thorough diagnosis, and a professional, detail-focused installation. Our experts are out in the field every week across Montréal, Laval, Longueuil, the North Shore, and the South Shore, providing customized, long-lasting solutions.
Key takeaways
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Trust a certified installer like AirGreen to size and install your unit properly.
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Never skip maintenance, even with a new system.
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Take advantage of available rebates to upgrade to better equipment without overspending.
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Think year-round performance, not just summer cooling.
For every project, AirGreen offers personalized guidance, full price transparency, and industry-recognized HVAC expertise throughout Québec.