Ottawa summers deliver stretches where the humidex sits well above the actual temperature and doesn’t let up for days. During those stretches, even a healthy air conditioner works hard, and a marginal one gives up entirely. Knowing how to keep your home cool in Ottawa during a heat wave is partly about the AC and partly about everything else.
These are the measures that make a genuine difference — and the warning signs that mean your system needs help rather than patience.
Block the Heat Before It Gets In
The cheapest cooling is the heat you never let inside. Direct sunlight through windows is a major contributor to indoor heat gain, and most homes leave that gain unmanaged.
Close blinds and curtains on the east side in the morning and the west side in the afternoon. Light-coloured or reflective window coverings work better than dark ones, which absorb heat and re-radiate it into the room.
If certain rooms are consistently unbearable, exterior shading — awnings, an added tree, or exterior blinds — is dramatically more effective than anything you can do from inside, because it stops the heat before it reaches the glass.
Use the Cool Part of the Ottawa Day
Even during a heat wave, overnight temperatures here usually drop meaningfully. That’s a resource worth using.
If the outdoor temperature falls below the indoor temperature at night, open windows on opposite sides of the house and let air move through. A window fan blowing outward on the warm side and inward on the cool side accelerates the exchange considerably.
Then close everything up in the morning before the outdoor temperature climbs past the indoor one. You’re essentially storing overnight coolness in the building’s mass and defending it through the day.
Stop Making Heat Indoors
Every appliance that produces heat competes with your air conditioner. During extreme heat, shift what you can:
- Use the barbecue instead of the oven — an oven can raise a kitchen several degrees for hours
- Run the dishwasher and dryer late at night, or hang laundry outside
- Turn off unused electronics and computers
- Switch remaining incandescent bulbs to LED
- Take shorter, cooler showers — hot showers add both heat and humidity
None of these is dramatic individually. Together they reduce the load your system has to overcome.
Use Fans Correctly
Fans don’t lower air temperature — they move air across your skin, which speeds evaporation and makes you feel cooler. That distinction matters for how you use them.
Run ceiling fans counter-clockwise in summer to push air downward. Turn them off in empty rooms, because cooling nobody is just adding motor heat. Use bathroom and kitchen exhaust fans while showering and cooking to pull heat and humidity out directly.
A fan alongside your air conditioner lets you set the thermostat a degree or two higher for the same perceived comfort, which meaningfully reduces runtime over a multi-day heat wave.
Set the Thermostat Sensibly
The most common heat wave mistake is dropping the thermostat well below your usual setting in hopes of cooling faster. Air conditioners don’t work that way — they have one output. Setting 18°C instead of 23°C doesn’t cool faster; it just means the system runs continuously and may never reach the setpoint.
During extreme heat, a system may only manage a certain difference from the outdoor temperature. Asking for more than it can deliver means constant running, higher bills, and increased risk of the coil freezing.
Pick a realistic setting and hold it. Steady operation beats extreme setbacks in a heat wave.
Help Your Outdoor Unit Cope
Your condenser rejects heat outside, and it does that job worse when it’s struggling for airflow. During a heat wave, take five minutes to check it.
Clear leaves, grass clippings, and debris from around and inside the unit. Trim vegetation back to leave roughly two feet of clearance on all sides. Gently rinse the coil fins with a garden hose — not a pressure washer, which bends fins.
Don’t enclose the unit or cover it while it’s running. And don’t spray water into a running unit’s electrical components — shut power off at the disconnect first if you’re doing more than a light rinse.
A coil cleaned properly during annual HVAC services in Ottawa sheds heat far better than one that’s been collecting cottonwood and grass clippings for three seasons — and that difference shows up precisely when the weather is worst.
Manage Humidity, Not Just Temperature
Ottawa’s summer discomfort is as much about humidity as heat. Air at 24°C and high humidity feels considerably worse than the same temperature dry, because sweat can’t evaporate efficiently.
Your air conditioner dehumidifies while it cools, but only during sustained runtime. This is another reason short cycling hurts comfort: brief bursts drop temperature without removing moisture.
Running exhaust fans, avoiding indoor drying of laundry, and in some homes adding a dehumidifier for the basement all help. If your home feels cold and clammy rather than cool and comfortable, humidity is your actual problem.
When Your AC Needs Help, Not Patience
There’s a difference between a system working hard and a system failing. Call for service if you notice:
- The indoor temperature climbing despite the system running continuously
- Air from the vents that isn’t noticeably cool
- Ice on the refrigerant lines or coil
- The outdoor unit running while the indoor fan doesn’t, or vice versa
- Breakers tripping repeatedly
- New grinding or screeching noises
An AC not cooling in Ottawa during a heat warning is worth acting on quickly — both because indoor heat becomes a health issue and because service queues fill fast. Genuine failures during extreme heat warrant emergency HVAC service in Ottawa.
Staying Safe When Cooling Isn’t Enough
If your system fails and a repair can’t happen immediately, prioritize people over property. Move to the lowest floor of the house, since heat rises and basements stay considerably cooler. Drink water steadily rather than waiting for thirst.
Spend part of the day somewhere air-conditioned — a library, mall, or community centre. Check on older neighbours and anyone with health conditions; heat affects people very unevenly, and the people most at risk are often the least likely to ask for help.
Frequently Asked Questions
Should I turn my AC off when I leave the house?
Better to set it higher than to turn it off entirely. A house that heats up all day takes a long time to bring back down, and the system runs at full output for hours to recover. Raising the setting a few degrees while you’re out saves energy without creating that recovery load — and a programmable or smart thermostat automates it.
Why is my upstairs so much hotter than downstairs?
Heat rises, upper floors sit under a hot attic, and most duct systems weren’t balanced for summer operation. Partly closing some main-floor supply registers can push more air upstairs, though don’t close so many that you restrict overall airflow. Persistent stratification usually points to a duct design issue worth having assessed.
Does closing vents in unused rooms help?
Rarely, and it often hurts. Closing too many registers raises pressure in the duct system, which strains the blower and can cause the coil to freeze. It also increases leakage from any gaps in the ductwork. Closing one or two registers to balance airflow is fine; shutting off whole sections of the house is not.
How cold should my AC be able to make the house?
Most residential systems can maintain roughly a 10 to 12 degree difference from the outdoor temperature under extreme conditions. On a 35°C day, holding around 23°C indoors is reasonable performance. If your system can’t manage that difference, something is wrong — it’s worth having checked rather than assumed.
Is it worth buying a portable AC as backup?
For a single room during a failure, it can help — particularly for a bedroom so people can sleep. They’re inefficient and won’t cool a whole house, and single-hose models pull warm air in from elsewhere as they exhaust. Useful as emergency backup; not a substitute for a working central system.
Final Takeaway
Getting through an Ottawa heat wave comfortably is mostly about reducing the load on your air conditioner: block sun, use cool nights, avoid generating indoor heat, and keep the outdoor unit breathing.
But those measures assume the system itself is healthy. If your home is getting warmer while the AC runs non-stop, that’s not something better habits will fix.
Get AC Help Before the Next Ottawa Heat Wave
Ultra Air Heating & Cooling
53 Kinetic Way, Ottawa, ON K2J 0E1
Phone: (613) 762-3035
Book Online: ultraairhvac.ca/contact-us
Not confident your air conditioner will handle the next stretch of extreme heat? Contact Ultra Air today for a full system check while appointments are still easy to get.
