Choosing the right power for your wall-mounted heat pump isn’t optional—it’s essential. At AirGreen, we see firsthand every day the consequences of poorly sized wall-mounted heat pumps in homes and commercial buildings across Montreal, Laval, Longueuil, the North Shore, and the South Shore. Poor indoor comfort, excessive energy consumption, and premature wear and tear on equipment: the repercussions are numerous—and often expensive. This article walks you through exactly how to avoid this common mistake, with technical explanations, real-life installation examples, and professional advice based on our extensive HVAC installation expertise.
Why is proper sizing so critical?
A poorly sized wall-mounted heat pump will never deliver the performance or comfort you’re expecting. Too small, and it will run non-stop without ever reaching the desired temperature. Too large, and it will short-cycle, harming the unit’s longevity.
The consequences of improper sizing
Excessive energy consumption
An improperly sized heat pump for the area or volume of your space will consume more power. It struggles needlessly to heat or cool—without doing it effectively.
Unstable thermal comfort
Are there cold spots in winter or hot zones in summer, even though your equipment seems modern? The issue likely comes from a miscalculation of your heating/cooling load.
Premature equipment failure
A compressor that constantly starts and stops wears out much faster. This reduces your unit’s lifespan and increases the risk of breakdowns.
How to properly size your wall-mounted heat pump
1. Precise heat load calculation
At AirGreen, we always perform a thermal load calculation based on several factors:
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The square footage and ceiling height
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The building’s insulation level
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The number and quality of windows
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The home’s orientation (sun, shade, prevailing winds)
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The number of occupants
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Daily usage of the space (residential, office, commercial)
Example: in Montreal, for a well-insulated 900 sq. ft. condo, a 12,000 BTU unit may be sufficient. But for a poorly insulated 1960s bungalow of the same size in Longueuil, you may need 18,000 BTU or more.
2. Choosing the right model for your usage
We don’t stop at theory. We also evaluate how the equipment will be used: primary heating? Backup system? Summer-only cooling?
One client in Boisbriand (North Shore) used their heat pump mainly for winter heating. We installed a Gree Sapphire 24,000 BTU unit, capable of operating efficiently down to -30°C, with excellent SEER/HSPF ratings and eligible for a $2,172 LogisVert grant.
Case study: Mistake avoided in Laval thanks to proper sizing
A duplex owner in Chomedey, Laval was planning to install two 9,000 BTU units to cool two separate floors. After inspection, we found that the main floor was poorly insulated, faced full sun, and had large windows. As a result, the heating/cooling demands were far higher than expected.
We proposed a better solution: an 18,000 BTU Fujitsu KZAH R-32 wall-mounted heat pump for the main floor and a 12,000 BTU Zephyr unit upstairs. Result: optimal comfort, controlled energy use, and a $1,704 Hydro-Québec grant received for the primary unit.
Common mistakes to avoid
Relying only on square footage
A 500 sq. ft. room in an uninsulated basement has different needs than a top-floor space with sunlight exposure.
Choosing based on price, not needs
A cheaper but undersized unit will cost you more in energy and repairs in the long run.
Ignoring Quebec’s winter conditions
In Quebec, low-temperature performance is non-negotiable. Many models look great on paper but fail at -15°C. Prioritize high-performance units like the Bosch BIVA R-454B or the Gree Extreme.
What we do at AirGreen
Full technical inspection
We visit your property to analyze the layout. We measure, observe, and most importantly, listen to your needs.
Personalized recommendation
Every home is different. Our proposal is tailor-made, backed by calculations, references, and past experience.
Professional installation
Our certified technicians perform clean, professional installations, always meeting industry standards and deadlines. We also help you with the LogisVert grant application process.
Recommended brands and models
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Fujitsu KZAH R-32: highly efficient, quiet, perfect for primary heating.
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Gree Extreme / Sapphire: excellent operation down to -30°C, great value.
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Bosch BIVA IDS Premium: stable inverter system, low energy use.
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Sharp ZU1: compact and efficient, ideal for small spaces.
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Haxxair, Arcoaire, Comfortmaker, ACD, Zephyr: tailored options for your budget and needs.
Our field experience
Montreal (Rosemont)
Installed a Sharp ZU1 15,000 BTU unit in a rental property. Accurate sizing despite small, poorly ventilated rooms. Result: increased comfort, lower energy bills.
Longueuil (Vieux-Longueuil)
Replaced an old wall-mounted AC with an 18,000 BTU Gree Extreme heat pump in a sun-exposed triplex. Careful analysis of flat roof and insulation. Optimal performance over two winters so far.
Sainte-Julie (South Shore)
Detached home with poor insulation. After a full heat load study, we installed a Bosch BIVA IDS Premium 24,000 BTU system. Client satisfaction high, and energy bills dropped by 35%.
In summary: proper sizing is a smart investment
Choosing a properly sized wall-mounted heat pump is a strategic investment. Right sizing ensures better energy efficiency, steady comfort, longer equipment lifespan, and access to government grants.
At AirGreen, we put our on-the-ground expertise, technical accuracy, and personalized support to work for your comfort—and your budget.