A union representing high school teachers is calling on Ottawa's biggest public board to shut down schools without air conditioning after one of its members was sent to hospital with heat-related illness Monday.

The Ontario Secondary School Teachers' Federation (OSSTF) is making the request amid a record-breaking September heat wave that's seen temperatures in Ottawa climb to 33 C and the humidex reach nearly 40.

"If it says it's going to be 40-something degrees with the humidex, maybe think about closing schools," said Nancy Akehurst, local district president of the OSSTF.

It's affecting learning, it's affecting student health, it's affecting staff health. - Nancy Akehurst , OSSTF

She pointed out that while the board has an emergency closure plan in place for such events as a broken furnace or an ice storm, there's no such plan for extreme heat.

The union representing elementary teachers with the Ottawa-Carleton District School Board (OCDSB) also weighed in Tuesday.

You know it's hot in our classroom when students start brining in fans for school supplies <a href="https://twitter.com/OCDSB">@OCDSB</a> <a href="https://twitter.com/hashtag/heatwave?src=hash">#heatwave</a> <a href="https://t.co/zDvOpStIJg">pic.twitter.com/zDvOpStIJg</a> —@mrcogan34

"Students and teachers in many classrooms are subject to unbearable conditions," Elementary Teachers' Federation of Ontario (ETFO) president Sam Hammond said in a release Tuesday.

"Our changing climate is sending a strong message that the Ministry of Education needs to take action," he said.

Temperatures in the capital soared Monday, which was not only the hottest day of 2017 but also the hottest fall day on record in Ottawa. Heat warnings remained in effect Tuesday, and Environment Canada said it would be Thursday before the city sees a return to normal temperatures.

High school teacher hospitalized

On Monday a teacher at Ottawa's Ridgemont High School had to be hospitalized as temperatures inside some of the school's classrooms soared to 30 C.

Nadia Towajj, OCDSB Superintendent responsible for Ridgemont High School said the school would be opening up cooler classroom spaces, after a teacher is sent to hospital with paramedics Monday.

"This was an employee who had some pre-existing issues, and we certainly understand that heat can be an exacerbating factor," said OCDSB superintendent Nadia Towajj.

Towajj said the building's only air conditioner, which cools the school library, was broken. On Tuesday a crew was on the school's roof repairing the unit.

Some students moved to cooler classrooms in the basement, while some classes moved to shaded areas outside.

This basement classroom will be used as an option for Ridgemont High School teachers who find their classrooms too hot to teach, according to the principal, Nancy Brady. (CBC)

'It's affecting learning'

"People are suffering," Akehurst said. "It's affecting learning, it's affecting student health, it's affecting staff health."

The ETFO said its members have also been calling with concerns about the heat. At least one school where most windows don't open also has a broken air conditioner, the union said.

In August, the ETFO called on the Ministry of Education to:

Ensure all schools without air conditioning have a heat stress plan.

Set a maximum indoor temperature limit, with an option to close schools if that temperature is reached.

Providing air conditioning or heat reduction systems in all Ontario elementary schools.

There may be cases where it is necessary to send a students or employees home. - Sharlene Hunter, OCDSB

OCDSB spokesperson Sharlene Hunter wrote in a statement that "there may be cases where it is necessary to send a student(s) or employee(s) home."

The board said it has been in touch with Ottawa Public Health regarding strategies to manage the heat, including ensuring staff are aware of the symptoms of heat exhaustion, dehydration and heat stroke.

The board also said it will ensure plenty of opportunities for students to drink water throughout the day.

According to the OCDSB:

Thirty-eight of its schools are either fully air-conditioned or have some kind of mechanical cooling such as ceiling fans.

Sixty schools are at least two-thirds air conditioned.

Fifty-one have no air conditioning, though some have at least one designated "cool" room such as a library.

Among the 51 schools with no air conditioning in their classrooms, some administrative offices are air-conditioned.

The board told parents it will cut back on physically strenuous activities, and consider cancelling gym classes.

No AC at home, premier says

When asked about the issue in Queen's Park on Tuesday, Premier Kathleen Wynne said she had to move a meeting to a cooler room, and said she didn't have air conditioning at home, drawing boos from some opposition members.

"I recognize that it is very hot in schools that were built in a time when there weren't the kinds of heat events that we have ... but again, I have a lot of faith in the educators in our schools to make sure that children and teachers are kept safe," Wynne said.

The government has spent billions of dollars on school upgrades and it's up to individual boards to decide how to spend that money, she said.

"There has been money that has flowed to school boards where decisions are made about changes in their buildings."