What to do if you lose power or air conditioning in a heat wave blackout

Amid the heat wave currently blazing across Canada, experts say that additional stressors can lead to increased power outages and broken air conditioners.

A February 2025 Environment and Climate Change Canada (ECCC) report states that “prolonged periods of extreme heat events can strain the power grid as the demand for air conditioning and fan use increases,” which can cause local heat-related outages.

The result of additional stress on power grids can lead to the idea of a “cascading failure,” according to Jeff Siegel, a professor of civil engineering at the University of Toronto.

“When part of the grid goes down, the remaining electricity is routed through the rest of the grid and then that increases failure somewhere else because everywhere gets overloaded,” he said.

“Hopefully we won’t get to that point of things. But certainly, that has happened in history, where you end up with a failure that spreads through the electrical grid.”

Many sectors of Ontario and Quebec are yet again under orange alert heat warnings, which can lead to heightened probabilities of losing power throughout the summer.

“We are seeing increased frequency of these yellow, orange and red extreme heat events, and that we’re seeing increased frequency of grid issues,” Siegel said. “It’s definitely much more frequent.”

An extreme heat event is identified when daily temperatures reach heat warning thresholds for two or more days in a row with no relief overnight.

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However, just heat alone is not the sole stressor for power grids.

“In some places in Canada, we’ve seen, for example, lightning storms that are associated with extreme heat, and that leads to a potential trigger for wildfires,” he said. “There’s definitely a lot of factors that are causing increased frequency and then the increased consequences that come with that.”

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Widespread power outages occurred across parts of Ontario and Quebec on July 2 due to severe thunderstorms following the heat wave at the time, affecting thousands of residents.

“Even in individual buildings they can have local power outages in the buildings if it overloads their own power supply, and obviously that can knock out air conditioning for hundreds or thousands of people at a time,” he said.

If a home’s air conditioner fails during a heat event, steps can be taken to reduce the heat being felt within the home.

“At the hottest times of the day, you can feel that hot air from outside coming in, close your windows and close your blinds and shutters,” Anabela Bonada, managing director of climate science at the INTACT Centre on Climate Adaptation said.

“If you have an indoor air filter, a HEPA filter, you can also build your own air filter. Turning that on since you’re having your windows closed and there’s no real air flow will help keep the air clean inside of your home and then you could open the windows again in the evening if the temperatures have gone down.”

“We’re all putting a lot of strain on our electrical systems and we could experience blackouts, which means even if you have a really well-functioned air conditioner, it may not work during that time, which is when extreme heat is happening.”

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Doing maintenance once a year on air conditioners should also be “sufficient” to prevent potential outages during heat waves, with the spring season being “the best time” to do so.

Health Canada states that “although anyone can experience heat stress, the associated health risks are greatest for those over the age of 65, infants and young children, people with chronic conditions such as breathing or heart problems, and for those who work or exercise in the heat.”

The agency recommends preparing emergency kits before a heat wave in the event either power or air conditioning are unavailable, which can include “food, water and a battery operated or wind-up flashlight.”

A household emergency plan is also encouraged that is aimed to “consider ways to prepare for extreme heat” that suits all members of a household, including older adults, children, pets, and anyone with additional health needs.

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To stay cool, Xie recommends “opening windows at night and then using window fans to ventilate warmer spaces indoors,” alongside reducing physical activities.

“One of the main ways our bodies are able to stay cool is by sweating. Having that airflow over the skin encourages evaporation, cooling the body down, as well as makes us feel better as well,” he added. “People can also try things like soaking clothing in cold water or dampening the clothing.

“Applying towels dampened with cool water to their skin, and that acts as basically free sweat. So instead of your body having to produce water on the skin that then evaporates and cools you, you’re adding water to your skin that does the same thing.”