Ontario Sees Record Electricity Demand Amid Scorching Summer Heat

The summer of 2025 has brought unprecedented electricity demand in Ontario, reaching levels not experienced since 2013. According to the Independent Electricity System Operator (IESO), peak demand hit 24,862 Megawatts (MW) during a heat wave in late June. This surge in consumption reflects the extreme weather conditions affecting the region.

Michael Dodsworth, a senior advisor of communications with the IESO, noted in a statement on August 27 that earlier in the month, temperatures again soared above 30 C for several days, pushing peak electricity demand to 24,789 MW. Notably, the previous year’s highest demand was surpassed on eight occasions this summer.

Record Temperatures and Impact on Power Consumption

In an average summer, Toronto experiences temperatures exceeding 30 C approximately 17 times. This year, that threshold was crossed 24 times. Meteorologist Anthony Farnell highlighted that Toronto also recorded temperatures above 32 C on 14 occasions, which is double the typical annual average. The heat wave in June saw temperatures hit a nine-year high of 36 C, with a humidex peak of 46.

Farnell explained, “Every extra degree added to the high temperature puts an exponentially higher strain on the electrical grid.” Additionally, the warmer nighttime temperatures meant air conditioning units were in constant operation to maintain comfortable indoor environments. This summer, overnight temperatures remained above 20 C for 24 nights, significantly above the norm.

Farnell had forecasted a hot summer for Ontario and Quebec, predicting high humidity levels in July and August following a cooler May. He noted that southern Ontario experienced six heat waves this summer, with temperatures consistently running 1 to 3 degrees above seasonal averages.

Increased Electricity Usage and Financial Implications

The extreme heat has had a noticeable impact on electricity consumption. For residential customers served by Toronto Hydro, electricity usage in July increased by nearly 5% compared to the same period last year. Spokesperson Brie Davis stated that prolonged air conditioning use during the heat led to noticeable changes in household electricity bills.

Davis explained, “A residential electricity bill includes local distribution costs and provincial transmission and generation costs.” While local distribution charges remain fixed, transmission and generation costs fluctuate based on usage. Typical customers may see an increase of about $7 in those charges this summer.

Similarly, Hydro One, Ontario’s largest electricity utility, reported a roughly 3% rise in residential electricity consumption from May to July when compared to 2024. This increase equated to an average additional cost of $3 to $4 per month for customers.

Despite the surge in demand, Dodsworth emphasized that Ontario’s power network has managed to remain stable. “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 stated.

As summer draws to a close, with the official end date on September 22, Farnell anticipates cooler days ahead for southern Ontario. The combined effects of extreme heat and environmental factors, such as smoke from wildfires, have compelled many residents to keep their windows closed, further impacting energy consumption patterns.