Summer in Montreal is beautiful. But it's also damn sticky.
We're talking about a humidity level that hovers around 68 to 71 % during the hot months. When the Humidex climbs above 30, going outside feels like walking through hot soup. Coming home should be a relief, not a continuation of the same discomfort.
Your air conditioner does more than just cool the air. It controls humidity. It protects your health. It prevents mold from growing. But only if it’s properly maintained.
A poorly maintained air conditioner during a humid Montreal summer is like having an umbrella with a hole in it during a thunderstorm. Technically, you have one. But that doesn't really solve your problem.
Why Is the Humidity So High in Montreal in the Summer?
Quebec's climate has always been unique. But in recent years, it has become more extreme.
Montreal's Climate Explained Simply
Relative humidity is the amount of water vapor in the air compared to the maximum amount the air can hold at that temperature. In Montreal during the summer, relative humidity levels are often in the 70 % range.
The Humidex is what it actually feels like. When it's 28 degrees outside with 70 % humidity, your body easily feels 35 degrees or more.
We now experience between 20 and 30 days each summer when the Humidex exceeds 30. Ten years ago, this was less common. The data show an increase of about 15 % since 2020.
Urban heat islands make the situation worse. Concrete, asphalt, and dark roofs all absorb heat during the day and release it at night. Moisture gets trapped in the city. It has nowhere to go.
Older Buildings and Limited Ventilation
If you live on the Plateau, in Rosemont, or in Montréal-Nord, there’s a good chance your building was built before 2000. These old buildings have charm, but they also have ventilation systems that date from a bygone era.
Older apartments and houses often have a limited air circulation. No mechanical ventilation. Windows that open only on one side. Bathrooms without adequate exhaust ventilation.
When outdoor humidity is high, indoor humidity rises as well. And if your home doesn't have an effective way to remove it, it builds up. It seeps into your walls, closets, and ducts.
We see this all the time during our inspections. Older buildings in central neighborhoods almost always have problems with excessive moisture during the summer.
Humidity + Poorly Maintained Air Conditioning: A Dangerous Combination
Combining naturally high humidity with a neglected air conditioning system is a recipe for trouble. Seriously.
Mold, Odors, and Unhealthy Air
When the relative humidity in your home exceeds 70 %, you create the perfect environment for mold. Mold thrives in damp, warm conditions. Montreal summers provide exactly that.
Your air conditioner is supposed to remove moisture from the air as it cools it. But if the filters are clogged, the coil is dirty, or the drain is blocked, it can no longer do its job properly.
The result? Humidity remains high even with the AC running. Mold begins to grow in the dark, damp areas of your system. And every time the AC turns on, it blows that contaminated air directly into your living space.
Visit odors If you notice a musty or stale smell when your air conditioner starts up, that's not normal. It's a clear sign that something is growing in there.
For people who suffer from allergies or asthma, it quickly becomes unbearable. Mold spores in the air make symptoms worse. You might think it’s just the summer that’s affecting you, but it’s often your own ventilation system that’s making you sick.
Excessive Energy Use and Power Outages During a Heat Wave
A poorly maintained air conditioner has to work much harder to do the same job. Dirty filters block the airflow. The system has to work harder to force the air through.
Studies show that a dirty system can consume up to 15 % more energy than a clean one. Over the course of an entire summer, that adds up to dozens of dollars wasted.
And the worst time for an air conditioner to break down is right in the middle of a heat wave. When everyone is running their AC on full blast and temperatures are nearing 35 degrees, that’s when poorly maintained systems give out.
We always receive more emergency calls during heat waves. These are people who have neglected maintenance and find themselves without air conditioning when they need it most.
Air Conditioning Maintenance: The Facts (and Myths)
There's a lot of confusion surrounding air conditioning maintenance. Let's clear things up.
Facts proven by experts
Annual professional maintenance of your air conditioning system improves its efficiency by 15 to 20 %. This isn't just a rough estimate—it's documented by associations of heating and air conditioning contractors.
A well-maintained system keeps relative humidity at a comfortable level, generally between 40 and 50 %. At that level, you’re comfortable and mold can’t really take hold.
Checking the refrigerant level is not optional. If your system is low on refrigerant, it cannot cool or dehumidify effectively. Only a certified technician is legally permitted to check and adjust refrigerant levels in Quebec.
Cleaning the coils and filters directly improves indoor air quality. It’s not just a matter of performance—it’s a matter of health.
Common Myths in Quebec
Myth #1: «Air conditioning makes you sick»
No. A DIRTY air conditioning system can contribute to respiratory problems. But a clean, well-maintained system improves air quality by filtering out allergens and controlling humidity.
What makes people sick is often mold and dust that build up in neglected systems. Or temperatures that are too cold, which cause a thermal shock when you go in and out.
Myth #2: «If it gets any colder, everything will be fine.»
Not at all. Your air conditioner can still blow cold air even if it’s dirty or has problems. It’ll just have to work much harder, use more energy, and probably break down sooner than expected.
It's like saying your car is fine just because it still runs, even though you've never changed the oil. Sure, it runs—but for how long?
Myth #3: «Fans are enough in the summer in Montreal»
Fans circulate the air. They create a cooling sensation on your skin. But they don't change the temperature or humidity in your home.
When it's 32 degrees outside with 70 % humidity, a fan just stirs up hot, humid air. It helps a little, but it doesn't solve the underlying problem.
Wall-mounted air conditioner, heat pump, or central air conditioning: which one manages humidity best?
Not all air conditioning systems are equally effective against Montreal's humidity.
Wall-mounted air conditioner (split system)
This is the most common system in condos and apartments in Montreal. An indoor unit and an outdoor compressor. Simple, relatively affordable, and efficient.
Visit wall-mounted units Modern units have a built-in dehumidification feature. When properly maintained, they do an excellent job of controlling humidity in small- to medium-sized spaces.
The problem is that many people never clean their wall-mounted units. The filters get clogged, the coils accumulate dust, and the drain gets blocked. And when that happens, the dehumidification capacity drops drastically.
We recommend having wall-mounted units professionally cleaned at least once a year, ideally in the spring before the hot season begins.
Heat Pumps: The Quebec Solution
Heat pumps are growing in popularity in Montreal. It is estimated that about 25 % of homes have now installed one.
The advantage is that it provides heating in the winter AND air conditioning in the summer. One system, two functions. And with Quebec winters alternating between very cold and less cold, the heat pumps Modern ones are now powerful enough for us.
In terms of humidity in the summer, heat pumps essentially function like air conditioners. They remove moisture while cooling the air.
Hydro-Québec offers grants of up to 2,000 $ for the installation of eligible heat pumps. This is a significant incentive that makes the investment much more affordable.
Maintenance remains crucial. A poorly maintained heat pump performs just as poorly as a neglected air conditioner.
Central and Ducted Systems
Central air conditioning systems are often found in single-family homes or large apartments. The conditioned air flows through ducts to reach all the rooms.
These systems generally provide better overall humidity control because they treat the air throughout the entire house evenly.
On the other hand, if your ducts are dirty or there are leaks in the system, your ability to control humidity decreases. Maintenance becomes even more critical—you need to clean both the central equipment AND the ducts.
👉 Not sure what kind of system you have or how to maintain it? We can check it for free.
How often should you have your air conditioner serviced in Montreal?
The 100 $ question. Literally, because that’s roughly how much it costs to ignore maintenance until something breaks.
What the Pros Recommend in Humid Weather
For a standard residence in Montreal, an annual maintenance check is the bare minimum. Ideally, this should be done in the spring, just before the start of the warm season.
If you live in a building with high humidity, if you’ve had mold problems in the past, or if your home has limited ventilation, biannual maintenance is recommended—once in the spring and once in the fall.
Properties near water, in neighborhoods with lots of trees and shade (which retain moisture), or those with damp basements should opt for biannual maintenance.
Basic maintenance should include:
- Cleaning or Replacing Filters
- Cleaning the Indoor and Outdoor Coils
- Checking the Condensate Drain
- Checking the Refrigerant Level
- General Performance Test
Actual Costs and Potential Savings
An annual professional service call typically costs between 150 $ and 300 $, depending on the type of system and the company.
It might seem expensive. But think of it as insurance.
A well-maintained system uses 10 to 15 % less energy. Over the course of a full summer, that easily adds up to 50 to 100 $ in savings on your electricity bills.
Best of all, it extends the life of your equipment. A well-maintained wall-mounted unit can easily last 15 years. A neglected unit? 8 to 10 years, if you're lucky.
Replacing a wall-mounted air conditioner costs between 2,500 $ and 5,000 $. Compared to that, 150 $ a year for maintenance is a real bargain.
👉 Schedule your appointment before the next heat wave—spots fill up fast in June
Regulatory Specifics and Trends in Quebec
Quebec has always done things a little differently. Air conditioning is no exception.
New Environmentally Friendly Refrigerants (2025)
The federal government, in collaboration with the provinces, is pushing for the phased-out of refrigerants with high global warming potential.
New refrigerants such as R-32 and R-454B reduce greenhouse gas emissions by up to 50 % compared to older refrigerants such as R-410A.
If you buy a new system in 2025 or later, there’s a good chance it will use these new refrigerants. That’s good for the environment.
On the other hand, it does change the way maintenance is performed. Technicians must be specifically trained to handle these new refrigerants. That’s one more reason to work with certified professionals.
Local Grants and Incentives
Hydro-Québec offers financial assistance programs for the installation of energy-efficient air conditioning systems and heat pumps.
For heat pumps, subsidies of up to 2,000 $ are available. Eligibility criteria change regularly, but generally, the system must meet certain energy efficiency standards.
There are also municipal programs in some boroughs to help homeowners improve the energy efficiency of their buildings. It’s worth checking to see what’s available in your area.
The Régie du bâtiment du Québec (RBQ) requires that any major installation or repair of an air conditioning system be performed by a contractor with the appropriate license. This isn’t just a formality—it’s for your safety and to ensure that the work is done according to standards.
How Vortex Air Helps You Better Manage Humidity in the Summer
We know the unique challenges of a Montreal summer. We live here. We breathe the same humid air as you do.
A Health + Performance Approach
Our priority is your comfort and health. It's not just about your air conditioner blowing cold air.
When servicing a wall-mounted unit, you should give it a thorough cleaning. This includes the filters, of course, but also the coils, the fan, and the indoor unit. Check the drain to make sure condensation is draining properly.
We also inspect your ventilation ducts If you have a central system. Because a clean air conditioner that blows air through dirty ducts won't solve your air quality problem.
We can also clean your air exchanger, if you have one. These systems work in tandem with your air conditioning to control humidity and refresh the indoor air.
Transparent and certified process
We'll show you exactly what we're doing and why we're doing it. Before we get started, we'll run a free system check and explain what needs attention.
We’re INVC-certified, and our NADCA certification is in the process of being finalized. We follow industry-recognized protocols because that’s how we sleep soundly at night—knowing we’ve done the job right.
We never pressure you into buying anything. If your system just needs a little cleaning, we'll tell you. If there's a more serious problem, we'll explain it clearly and go over your options with you.
Mohamed and Omar are available to answer your questions directly. You'll be speaking with the owners, who understand your situation—not a call center.
We're open 7 days a week, from 7 a.m. to 9 p.m. Plus, our inspection is always free. You've got nothing to lose by calling us to assess your situation.
👉 Schedule your free inspection—we'll give you an honest assessment of what you need
FAQ – Humidity, Air Conditioning, and Summer in Montreal
What is a normal indoor humidity level in the summer?
Between 40 and 50 % is ideal. At this level, you’re comfortable and mold can’t really grow. If your indoor humidity regularly exceeds 60 %, there’s a problem with your ventilation or air conditioning system that should be checked.
Is a dehumidifier enough without air conditioning?
For small spaces like a basement, yes. But to cool AND dehumidify an entire home during the Montreal summer, a dehumidifier alone won’t cut it. You’ll just be removing moisture without lowering the temperature. It helps, but it’s not a complete solution.
Does air conditioning use more energy during humid weather?
Yes, a little. When outdoor humidity is high, your system works harder to remove moisture from the air in addition to cooling it. That’s normal. However, a poorly maintained system will consume MUCH more energy than a well-maintained one under the same conditions.
How can I tell if my air conditioner is clogged with dirt?
Clear signs: musty odors when the unit turns off, weaker airflow than before, water dripping from the indoor unit, electricity bills rising for no reason, or ice forming on the pipes. If you notice even one of these signs, it’s time to have your system inspected.
Is there a difference between a condo and a house?
A little. Condos often have individual wall-mounted units that cool just your space. Houses are more likely to have central systems. But regardless of the type of home, the principles are the same: regular maintenance is essential, especially in our humid climate.
Is it possible to reduce humidity without air conditioning?
You can help by using exhaust fans in the kitchen and the bathroom, by opening the windows when the humidity outside is lower (early in the morning or late at night), and by using a dehumidifier. But honestly, during Montreal’s intense humid heat waves, air conditioning is really the only effective solution.
Are heat pumps suitable for older homes?
It depends. Wall-mounted heat pumps can be installed in almost any home without altering the structure. That’s precisely their advantage—no ductwork is needed. However, if your insulation is really poor, you’ll have a hard time maintaining a comfortable temperature no matter what system you use. In that case, improving your insulation should be your first step.
Breathe Easier This Summer
Summer in Montreal is coming. The humidity will rise. Those sticky days will be back.
Your air conditioner will be your ally—if it's ready to do its job.
At Vortex Air, we’ve helped more than 500 Montreal families better manage their comfort and air quality. We understand the specific challenges of our climate. We’re familiar with the typical issues found in Quebec buildings.
We'll give you the straight facts about the condition of your system. No high-pressure sales. No hidden fees. Just honest advice from people who have lived and worked in Montreal for years.
The inspection is free. The call is free. And even if you decide not to do anything right away, at least you'll know exactly where you stand.
Call us on 514-214-7492 or visit vortexair.ca to plan your free inspection before summer really kicks in.
Because a comfortable summer in Montreal starts with an air conditioning system that works properly.
