How CBC measured heat in homes in 5 Canadian cities

A CBC News investigation has revealed how much hotter some Canadian homes are than the air outside subjecting those living inside to unsafe temperatures around the clock.

Data from scientific-quality sensors installed by CBC in 50 homes with little or no central cooling showed many people in those homes remained at temperatures considered unsafe by human physiology experts late into the night and sometimes for days at a time.

The data from sensors in five cities Vancouver, Winnipeg, Toronto, Montreal and Windsor showed more than half the households were measuring at or above 26 C, the maximum indoor temperature widely considered safe by experts, more than half the time the sensors were there.

Sustained exposure to temperatures above 26 C is particularly dangerous for the elderly and those with chronic health conditions, said Glen Kenny, a professor and research chair in human environmental physiology at the University of Ottawa.

"As we get into hotter conditions, it creates a greater strain on the body. And as we get older, we lack our ability to activate our heat loss responses as robustly as we would when we were younger."

For most people, the cooler night air offered little to no relief. CBC's investigation found indoor temperatures generally peaked around 7 p.m. and took several hours to drop leaving residents struggling to sleep.

And in eastern Canada, CBC's investigation found high rates of humidity added as much as five to seven degrees to already sweltering indoor temperatures.

There is little data in Canada on indoor air temperatures, but B.C.'s summer 2021 heat dome, in which the coroner attributed 619 deaths to the heat, shows why it is important.

Almost all of those deaths occurred indoors in places without adequate cooling, the coroner found. But the only data available on how hot it was inside those homes, and for how long, came from a handful of people who installed smart thermostats and agreed to anonymously share the data with researchers.

CBC set out to find out how hot homes are getting, tell the stories of those affected and look into what can be done to help them.

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CBC's heat tracking investigation

CBC News purchased 50 scientific-quality temperature and humidity sensors and tested them in Vancouver to ensure they were all in good working order and measuring consistently.

CBC journalists in each city identified 10 households in each city who met the following criteria:

• Willing to have a sensor in their home.
• Said their homes were uncomfortably hot in the summer.
• Willing to share their stories of coping with the heat with CBC News over the summer.
• Had zero or minimal central cooling (heat pump or air conditioning) in their homes.

Seven of the 50 homes where CBC installed sensors either had a window-mounted air conditioning unit in one room of the home, or installed one over the summer.

Most of the sensors were installed by CBC in late June and took temperature and humidity readings every 10 minutes over an eight-week period until mid-August. Some people moved over the summer, so those sensors were removed sooner. One sensor stopped taking measurements after it fell and lost its batteries, so CBC's data is based on 49 sensors in five cities.

CBC journalists collected data from the sensors via a mobile app.

When CBC data journalists combined and analyzed the data from all 49 sensors, we noticed that during the first couple of hours of logging, the temperature varied significantly before settling into a consistent pattern. During the testing process in Vancouver, we also noticed the sensors took more than an hour to adjust to the conditions of a new location moving from a sunny to a shady part of a room, for example. For both these reasons, we decided to exclude the first 12 sensor readings (two hours) from each sensor.

CBC used temperature and relative humidity measurements from the sensors to calculate a heat index, or "feels-like" temperature that incorporates humidity, for every sensor reading. CBC used heat index, an American measurement, rather than humidex because our methodology was based on a previous investigation done in New York.

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To obtain data on outdoor temperatures, CBC data journalists located the closest Environment Canada weather station with hourly readings to each household and pulled in that data.

CBC News then put our findings and analysis to three university professors with experience measuring indoor heat for their review and critique. We incorporated their suggestions into our final analysis.

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