Installing a multizone heat pump is a major investment in your comfort, health, and energy savings. However, one critical factor is often overlooked by homeowners: the proper sizing of the HVAC system. At AirGreen, we’ve seen time and again that choosing the right capacity (not too much, not too little) has a direct impact on energy efficiency, equipment longevity, and indoor comfort. This article dives into the real-world consequences of proper sizing for a multizone heat pump, with specific examples from our installations in Montréal, Laval, Longueuil, on the North Shore and South Shore.
Why is sizing so critical for a multizone heat pump?
When it comes to a multizone heat pump, the most common mistake is relying solely on the square footage of the rooms to be heated or cooled. Yet, other key factors come into play: house orientation, insulation, windows, number of occupants, appliances, actual use of rooms, etc. Proper sizing ensures optimal performance, and more importantly, prevents costly issues in the long term.
The consequences of an oversized heat pump
Oversizing means installing a heat pump that’s too powerful for the actual needs of the home. It may seem reassuring — “better too much than not enough,” many think. But this choice greatly reduces the system’s efficiency. An oversized heat pump:
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Operates in short, frequent cycles, causing premature wear on components;
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Fails to reach optimal energy performance (SEER or HSPF ratings drop);
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Leads to poor dehumidification, making the air uncomfortably humid in summer;
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Wastes electricity, increasing your utility bills.
The risks of an undersized heat pump
On the flip side, an undersized heat pump won’t be able to meet the thermal demand of all zones during intense cold or heat waves. It:
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Runs continuously, resulting in excessive energy consumption;
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Fails to heat or cool certain areas effectively;
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Causes frequent complaints about cold or overheated zones in the home;
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Accelerates wear on the compressor and fans.
Case study: an optimized multizone installation in Laval
A concrete example: this January, we completed the installation of a Gree Multi+ Extreme multizone heat pump in Laval in a two-storey single-family home with a finished basement. The client wanted to connect four wall units: living room, master bedroom, home office, and basement family room.
During the initial assessment, a previous contractor had recommended a 36,000 BTU outdoor unit without a detailed thermal study. However, our team performed a full thermal load calculation, which revealed that 28,000 BTU would be sufficient, thanks to the building’s excellent insulation and south-facing exposure.
The result: we installed a Gree Multi+ Extreme 30,000 BTU outdoor unit, paired with indoor units of 9,000 and 12,000 BTU depending on the room. The system now operates with high energy efficiency, the client reports uniform comfort, and their Hydro-Québec bills have dropped by nearly 25% compared to the previous winter.
How does AirGreen handle sizing?
At AirGreen, we leave no room for guesswork. Our technical advisors perform a comprehensive assessment of your home before making any recommendation:
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Room-by-room thermal evaluation, factoring in construction materials, orientation, insulation, windows, and usage habits;
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Calculation of BTU needs for each zone;
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Recommendation of an optimized multizone heat pump configuration (e.g., Gree, Fujitsu, Mitsubishi, or Tosot, depending on your needs and available grants);
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Assessment of grant eligibility, such as Hydro-Québec’s LogisVert program (up to $5,000 in financial aid).
Our recommendations to avoid common mistakes
Always demand a complete thermal analysis
Never rely solely on room size or a generic suggestion. A professional thermal evaluation is essential.
Choose a certified professional
Proper sizing requires extensive HVAC training and real-world experience. Our installers are TEQ certified and participate in ongoing training on the latest standards (R-32, R-454B, SEER/SCOP efficiency, etc.).
Think about future expansion
If you’re planning to finish a basement, attic, or add an extension, we can build capacity reserves into your multizone system, avoiding costly upgrades later.
Multizone heat pumps: a delicate balance… but a smart investment
A properly sized system delivers:
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Optimal energy efficiency, often above 300%;
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Stable and silent thermal comfort in every zone;
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Increased equipment lifespan (15–20 years with regular maintenance);
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Maximum eligibility for government grants;
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A significant reduction in annual energy costs.
Customer testimonial – Longueuil
“We hired AirGreen to replace our old wall-mounted ACs with a multizone heat pump. Their team took the time to do a thorough analysis. The equipment installed is perfectly tailored to our needs. It’s warm everywhere in winter, cool in summer, and our electricity use has dropped.”
— Sophie and Alain B., Longueuil
AirGreen: your multizone heat pump expert in Montréal and surrounding areas
Whether you’re in Montréal, Laval, Longueuil, on the North Shore or South Shore, our HVAC installation experts support you from start to finish in the selection, sizing, and maintenance of your multizone heat pump. Trust a company known for its integrity, technical accuracy, and transparency.