The summer of 2025 has been incredibly hot with record breaking heat waves! Your air conditioner in Ottawa has been working overtime and you may have noticed the temperature on your thermostat is not dropping like it used to. This article dives into the reasons your air conditioner may not be cooling your home quickly and what you should expect in terms of air conditioner run time.
How long should an air conditioner in Ottawa take to cool my home?
Every air conditioner in Ottawa will operate differently due to numerous factors but on average you should see 0.5–1 degree cooling per hour. On days above 29C your unit may work overtime just to maintain the homes current temperature.
This slow and steady drop in temperature is normal — and actually a sign your system is doing its job properly. When your air conditioner starts up, it doesn’t just blow cold air; it first removes excess humidity from your home. Warm indoor air is pulled across a very cold evaporator coil, where moisture condenses and drains away. Only after enough moisture is removed does the temperature inside begin to fall.
This process takes time — especially on hot, muggy Ottawa days. High humidity makes it feel warmer than it really is (for example, 23 °C can feel more like 27 °C). That’s why the dehumidification step is so important for real comfort, not just numbers on a thermostat.
It’s also why your air conditioner might need to run for a few full cycles before you notice a meaningful temperature change. And if your system is undersized, poorly maintained, or fighting extreme outdoor heat, it can take even longer to catch up.
If your air conditioner in Ottawa seems to be running non-stop without results, it might be time to check for dirty filters, duct issues, or improper sizing. At AirZone, we can help diagnose the problem and get your home cooling efficiently again — even in the thick of an Ottawa heatwave.
What factors affect how quickly my Air Conditioner in Ottawa cools my house?
Every home is different, and so is every cooling system. If your air conditioner seems to be taking longer than it should to cool your house, here are the biggest factors that could be affecting its performance:
- Outdoor Temperature:
Ottawa air conditioners are typically sized to handle temperatures up to 26 °C — the official “outdoor design temperature” used in Canada’s building code. On extreme heat days, especially when we hit the high 30s, your AC will naturally take longer to cool your space. - Humidity Levels:
Before your system can lower the indoor temperature, it has to remove excess moisture from the air. On muggy days, your AC needs extra time to dehumidify before the air feels cooler. - Ductwork Design & Condition:
If your ductwork is leaking or blocked, cold air won’t reach every room evenly. This can make your AC work overtime, reduce efficiency, and leave hot spots throughout your home. - Insulation & Windows:
Poor insulation and older windows can let heat in and cool air out. Homes with large south-facing windows or inadequate attic insulation will warm up faster and cool down slower. - Ceiling Height & Layout:
Open-concept spaces and vaulted ceilings look great — but they can be harder to cool. The larger the air volume, the longer it takes to bring temperatures down. - Appliances & Daily Habits:
Cooking, running laundry, or using electronics adds heat to your home. Keeping blinds closed and using ceiling fans can ease the load on your AC. - System Maintenance:
A dirty filter, clogged coil, or overdue tune-up can significantly reduce cooling speed and overall performance.
At AirZone, we evaluate all of these factors before recommending new equipment or system upgrades. Our goal is to make sure your air conditioner keeps you cool — even during Ottawa’s hottest weeks. Want to book an AC maintenance?
Is my air conditioner in Ottawa too small for my home?
The only way to know for sure is to have a system designer — like one of our experienced team members at AirZone — evaluate your home and perform a proper load calculation.
While a common rule of thumb in Ottawa is 1 ton of cooling for every 700-1000 square feet, this is just a starting point. A 2,000 square foot home may appear to need a 3.5-ton unit on paper, but the right size depends on much more than square footage. Proper system design includes evaluating your home’s insulation levels, ceiling height, number of windows, orientation to the sun, ductwork layout, and how airtight your home is. For example, a newer home in Barrhaven with high-efficiency windows and spray foam insulation will have drastically different cooling needs than a 100-year-old home in Westboro.
These factors directly impact how well your air conditioner in Ottawa performs, especially during our increasingly hot and humid summers. If your AC runs constantly, never reaches your set temperature, or certain rooms stay warm, it might be undersized — but only a detailed assessment will confirm that. Our team uses advanced diagnostic tools and real-world experience to ensure you’re not relying on outdated rules or guesswork. Whether you’re considering a replacement or just want peace of mind, we’re here to make sure your air conditioner in Ottawa is the right fit for your comfort.
What is the outdoor design temperature for cooling in Ottawa?
The outdoor design temperature for cooling in Ottawa is 28 °C. This number is used by HVAC professionals to size air conditioners that can keep your home comfortable during the vast majority of Ottawa’s days — specifically, temperatures that are exceeded only about 2.5% of the time in a typical summer. **Note the summer of 2025 has vastly exceed this 2.5% number**
Why does this matter? Your air conditioner is designed to maintain indoor comfort when the outdoor temperature is up to 28 °C. If the weather goes beyond that — like during a heatwave — your system may need to run longer to keep up. That doesn’t mean it’s broken; it means it’s working within its design limits.
This temperature isn’t just pulled out of thin air. It’s based on national standards used across Canada to protect occupant health and comfort. These guidelines help HVAC designers, like our team at AirZone, determine the right system size so that you’re not left sweating when Ottawa heats up. You can read more about how these temperatures are chosen in the ASHRAE design guide.
So, if your air conditioner seems to be working harder on days above 28 °C, that’s expected. But if it struggles at 26 °C or lower, it could be a sign of an undersized system, duct issues, or poor insulation. That’s where we come in — helping Ottawa homeowners stay cool with properly designed, right-sized solutions that match our local climate.
When should I call in a professional for AC sizing or repair?
If your air conditioner in Ottawa is constantly running, struggling to reach your set temperature, or leaving parts of your home too warm or humid, it’s time to call in a professional. These are signs that your system may be improperly sized, poorly performing, or in need of repair. At AirZone HVAC Services, we specialize in diagnosing these issues and recommending the right solution — whether it’s a detailed load calculation, a targeted repair, or a properly sized upgrade. Don’t sweat through another hot day — contact us today for expert help and honest advice.
