Southern Ontario is having one of its hottest days ever on Thursday, but the agency that monitors the province's power grid says it shouldn't be anywhere near record energy consumption.

"Overall demand has come down" over the last five or six years, said Alexandra Campbell, spokeswoman for the Independent Electricity System Operator, or IESO, the government agency that oversees the grid.

Though Windsor, London and Toronto are all expecting temperatures approaching 40 C, it doesn't mean Ontario businesses and residences will use a record amount of electricity.

"Everybody on the power grid is ready and we're in good shape, so it should be a really good day even though it'll be a really hot day," Campbell said Wednesday.

A shirtless man walks along the waterfront in Toronto on Tuesday. Hassan Arshad/CBC

The heat that has affected most of the country except the coasts has centred on southern Ontario, where the humidex level was already at 40 by 8 a.m. ET and 45 by noon.

At the IESO, the crew of six or seven that monitors and balances electrical supply and demand round the clock from a large NASA-like control room in Mississauga, Ont., expects the province's consumption to peak at 25,100 megawatts, well short of the all-time peak of 27,005 megawatts hit in Aug. 1, 2006.

People are conserving energy more often and the recession has shuttered some industries that used large amounts of electricity, Campbell said.

Even if Ontario does approach the record, the grid can handle about 28,000 megawatts on its own and pull in another 4,000 or 5,000 megawatts from Quebec, New York and Michigan. Campbell said the increased capacity is due to refurbished nuclear power plants, new gas generation and new solar, wind and hydroelectric power.

The 2003 blackout that left 50 million people in Ontario and eight states without power was more about slack regulation, which allowed a problem in Ohio to cascade through the system, than about the amount of electricity, Campbell said. Standards and monitoring have since been beefed up, Campbell said, although critics say not enough has been done.

Toronto Hydro eyes equipment

Power outages won't be due to lack of supply, she said. But the heat will undoubtedly cause strain on Toronto's roughly 80 electricity distributors and their equipment.

Toronto Hydro said in a news release that energy consumption in Canada's largest city may break last year's peak of 4,786 megawatts Wednesday, if not the record of 5,018 set in July 2006. The release also warned that relatively high overnight temperatures do not allow the transformers and other equipment to cool down.

Ontarians will have plenty of reason to switch on the air conditioning Thursday, as the province experiences some of its highest temperatures ever for July.

The expected high in Toronto and London is 37 C, and the temperature is forecast to peak at 39 C in Windsor.

Campbell said it's still advisable for residents to avoid wasting energy: Many Ontarians are charged more for peak-hours usage, and consuming less energy reduces bills now and infrastructure costs later. It's also better for the environment, she said.