The scorching summer of 2025 has led to levels of electricity usage not seen in more than a decade in Ontario.
The Independent Electricity System Operator (IESO), which manages Ontario’s power system, told Global News that this summer has been one for the record books.
“During the heat wave in late June this year, peak demand reached 24,862 Megawatts (MW), the highest peak since 2013,” Michael Dodsworth, senior advisor of communications with the IESO, said in an Aug. 27 statement.
“Earlier this month, temperatures again surpassed 30 C for several days, with peak electricity demand topping 24,789 MW. The highest electricity demand from last year was surpassed eight times this summer.”
During an average summer in Toronto, surpassing 30 C happens about 17 times, Global News meteorologist Anthony Farnell said.
This summer, Toronto topped 30 C 24 times; that only happened 10 times last year, and half of those days were in June, he said.
Furthermore, Farnell said Toronto topped 32 C 14 times this summer, doubling the annual average. During a heat wave in June, temperatures hit a nine-year high of 36 C and the humidex hit an all-time June high of 46, he added.
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“Every extra degree added to the high temperature puts an exponentially higher strain on the electrical grid,” Farnell said.
“Also, warmer overnight temperatures mean AC units are working overnight 24-7 to bring the inside temperatures down. The temperature stayed above 20 C for 24 nights this summer, which is also double the average.”
In June, Farnell forecasted a hot summer for Ontario and Quebec, saying that while June would be a transitional month after a cool May, July and August would bring humidity levels above normal.
Looking back, Farnell said southern Ontario had six heat waves this summer, with temperatures running one to three degrees above normal for the season.
Heat aside, Farnell added that smoke and poor air quality from several wildfires meant more households kept their windows closed, even when the weather turned cooler outside.
For residential Toronto Hydro customers in July, nearly five per cent more electricity was used compared with the same time last year, spokesperson Brie Davis said.
“This is largely due to more frequent and prolonged use of air conditioning during extreme heat we have experienced in 2025,” she said in a statement.
Davis added that this led to a change in consumer bills.
“A residential electricity bill includes local distribution costs and provincial transmission and generation costs. The local (Toronto Hydro) distribution charges are set on a fixed basis, so they do not go up or down based on customer usage, even when the weather is very hot,” she said.
“The provincial transmission and generation costs do change based on customer usage. Compared to last July, a typical customer may see an increase of about $7 in those charges based on greater electricity consumption due to extreme heat.”
Hydro One, the province’s largest electricity utility, saw roughly a three per cent jump in residential electricity usage between May and July when compared with that same time in 2024, spokesperson Bianca Pizzo said. That translated to an average increase of $3 to $4 a month, she added.
Both Hydro One and Toronto Hydro said they have several programs available for customers looking to help save on energy costs.
Despite the increased usage this summer, Dodsworth said Ontario’s power network has held up well.
“Even with this high demand, the IESO control room has been able to leverage Ontario’s diverse supply mix that includes wind, solar, hydro, natural gas, nuclear, and energy storage to keep the lights on,” he said.
“These different resources have different characteristics and responses to weather, meaning we always have resources to draw on that are right for the moment.”
As for the rest of the summer, which officially ends Sept. 22, Farnell said more chilly days are in store for southern Ontario.
© 2025 Global News, a division of Corus Entertainment Inc.