Ontario's Independent Electricity System Operator (IESO) says three vital nuclear units - representing eight per cent of the province's power supply - are down at the Pickering Nuclear Power Plant, which could lead to power outages in the GTA.
The IESO says if the humidity rises with the mercury, residents could be asked to limit their power intake for the second time this summer.
"We obviously pay very close attention to the weather," Terry Young, a spokesperson from IESO, told CTV News.
Toronto has already experienced one power advisory this summer when residents were asked to limit their consumption to prevent rolling black outs.
According to the IESO every three-degree increase of humidity increases power demand 450 megawatts, which is equivalent to one nuclear reactor.
Forecasters are calling for temperatures in the mid-thirties the first week of August.
Tom Adams, a spokesperson from Energy Probe, says Toronto is particularly vulnerable because there aren't enough power lines to import energy from New York or other generators.
In order to meet increased demand the province will be firing up its coal plants, which are a major contributor to poor air quality.
Wind turbines are ruled out as a reliable source of energy.
On a hot day, the city uses 26,000 megawatts and on July 30 at noon the turbines were producing only nine megawatts of energy.
But for residents who love the heat, there are plenty of outdoor activities in the GTA designed to keep you cool.
City pools are open and the new HTO Park and beach at Spadina and Queen's Quay provides ample room for catching some rays.