Day three of scorching hot temperatures means a third day for heat warnings in Caledon, Durham Region and York Region.

Environment Canada issued the heat warning on Monday after a hot airmass moved into southern Ontario. Meteorologists say daytime temperatures are expected to float just above 30 C, while lows overnight will hover around 20 C. This hot and sticky weather is expected to stick around until Thursday.

The weather service says infants, children, older adults, people who work outside and individuals with chronic illnesses are at the greatest risk of developing heat illnesses.

According to the Simcoe-Muskoka District Health Unit symptoms of heat illness include dizziness, vomiting, headaches, rapid breathing and extreme thirst.

Newmarket has opened a number of cooling stations across the municipality. Residents can cool off at the Magna Centre from 6:30 a.m. to 10 p.m. Monday through Friday and at the Ray Twinney Complex from 8 a.m. to 5 p.m. on Saturday and Sunday.

In Ramara there's a cooling station open at the Administrative Centre and at the Ramara Centre. In Wasaga Beach, cooling stations are set up at the Wasaga Stars Arena and Recplex.

“We felt it was prudent to open them up and give people a chance to cool down,” says Ramara Fire Chief Dave McCarthy.

The heat is also taking a toll on the power grid. PowerStream says it saw the highest peak of demand in two years on Monday.

“Especially when you have consecutive days of hot weather it just ramps up because air conditioners have to work harder,” says spokesperson Eric Fagen.

Hydro officials say there is more than enough electricity in the province to meet the demand, however they are asking customers to conserve energy. 

“Even though we have enough capacity it is a strain on the grid. I encourage people to set thermostats to twenty six degrees. That will still be a comfortable temperature.”