What's the right temperature for your air conditioning?

Is your office freezing? Do you need to keep cool to stay healthy? Should you set your thermostat based on recommendations from your utility? If you're lucky enough to have air conditioning, there are a number of factorsto consider when choosing the right temperature.

Comfort and avoiding negative health impacts that come with heat exposure are key. But the hotter it is outside compared to your thermostat setting, the more power air conditioners guzzle. That could strain electricity grids and increase the risk of deadly blackouts during heat waves.

In places with a dirty grid, the energy used to cool buildings can make power plants burn more fossil fuels, which in turn impactsglobal heating from climate change. Plus,using lots of powercan generate big energybills.

So what to do?

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Recommended temperatures all over the map

There's no shortage of recommendations and guidelines for your thermostat setting spanning a wide range.

28 C: Recommended by the Japanese Ministry of the Environment to save energy. It was implemented in offices and shops, along with encouragement to wear less formal office attire. This is also recommended in South Korea, with exemptions for some kinds of buildings such as schools and daycares, senior centres and hotels. Toronto Hydro recommends this as the temperature to set when you're away from home.

27 C: Recommended by the World Health Organization, which also suggests adding a fan to make it feel 4 C cooler. Spain has made it illegal to set thermostats lower than this in public places, although it's only a recommendation at home. Greece and Italy (excluding hospitals) also use this set point for public buildings.

26 C: The maximum summer thermostat setting recommended by Toronto Hydro, and the Canadian Standard Association's standard for workplace ergonomics in occupied buildings. Some groups also want to legislate this as the maximum allowable indoor temperature in Toronto.

25.5 C: Recommended by Energy Star, an energy efficiency-labelling partnership between the U.S. Environmental Protection Agency and private companies that make appliances. It'salso recommended by the Hong Kong Government, which says it aims to strike a balance between energy savings and CO2 emissions reductions, as well asthermal comfort.

25 C: Recommended by BC Hydro, which also suggests shutting off the air conditioner when you're not home for an hour or more.

24.5 C: The "optimum" summer temperature, according to the Canadian Standards Association's standard for workplace ergonomics. (Its suggested range is 23 C to 26 C.)

24 C: Recommended by the American Society of Heating, Refrigerating and Air Conditioning Engineers for when you are home during the day. It recommends a higher temperature at night.

22 C: This is considered the typical temperature for air-conditioned spaces in North America. It's based on what studies have found comfortable, but there are criticisms that this is based on small studies of men in suits, and there's lots of evidence that women like it warmer.

26 C is OKfor most

"I unfortunately don't think there's a magic set point," said Brendan Haley, director of policy for Efficiency Canada. He noted that it can depend on many factors, including some that can change over time, such as age and health status.

Seniors and those with certain chronic health conditions such as heart or kidney disease, as well as those with schizophrenia, are more likely to die during heat waves and are considered more vulnerable to heat.

Glen Kenny, professor of human physiology at the University of Ottawa said health agencies have generally considered indoor temperatures of 24 to 28 to be safe for vulnerable people, but that's based on statistics.

So he recently ran a test on a group of seniors aged 65 to 85. After eight hours at 26 C, they had no increase in core body temperature, heart rate or blood pressure, suggesting that 26 C is a safe room temperature for a day-long exposure.

However, he said, "26 C is still a very warm temperature and potentially uncomfortable for people."

He added that longer exposures could disrupt vulnerable people's sleep. "That can worsen their overall health."

It's something he hopes to look into next.

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Temperature recommendations canbehigher than 26 C in some countries, depending on factors such as the capacity of their power grids and their climates.

Kenny acknowledged that people in some countries are used to hotter temperatures. "There is going to be a level of adaptation, acclimatization to that environment," he said, although that can take weeks.

Keeping it warmeases power bills andgrid impacts

Too many air conditioners running too hard have led to deadly outages in countries such as Pakistan. In Canada, they've been blamed for small outages like one in Ottawa's west end last year. In B.C. last year, some landlords warned tenants against installing air conditioners, saying older buildings don't have the electrical capacity to handle them.

That may be why many utilities recommend keeping your thermostat set closer to 26 C than 22 C.

Climate scientist Andrew Dessler explains that air conditioners need to work exponentially harder the hotter it is outside compared to the temperature you set inside, consuming exponentially more power and leading to higher bills.

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"Air conditioning is expensive and, because of climate change, it's getting a lot more expensive," he wrote this week in his newsletter The Climate Brink.

He gave the example of someone who wants to cool their house to 24 C. If the outside temperature increases from 36 C to 38 C due to climate change, that will require 42 per cent more energy, he calculated.

Already, he said, the power bills for air conditioning are unaffordable for some.

Jim Bolger, president of the Ontario HVAC sales and service company Waterloo Energy Products, acknowledged that for some people, a $10 or $20 difference in their power bill could be significant.

Your equipment and your home make a difference

Bolgersaysthat adjusting your thermostat up or down may not make that much of a difference to your power consumption it also depends on the age and efficiency of your air conditioner and how well insulated and shaded your house is.

He suspects that what hydro utilities are worried about is the thousands of people who have old, inefficient air conditioners who will also get much higher bills if they crank their air conditioners too hard.

If your air conditioner relies on a geothermal or geoexchange heat pump, as his does, it will be dumping heat into the ground (instead of the air). The ground is much cooler than the air in the summer, making geothermal systems extremely efficient. In that case, "you're saving nothing" by increasing your thermostat a few degrees, Bolger said.

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Likewise, people with newer, efficient air-source heat pumps or air conditionersprobably won't see a huge impact if they keep their place a bit cooler. Thosealso dehumidify your home more effectively (and many even have a dehumidification mode), which can make a big difference, he said: "You can feel more comfortable at 24 degreeswith lower humidity than you can at 20 with high humidity."

Haley withEfficiency Canada noted that it's not just the air conditioner itself that makes a difference. It's also how well your house keeps the coolness in and the heat out its airtightness, insulation and how well shaded it is. "That is, I would say, huge," he said.

What about at night? And when you're away from home?

Some placescharge higher electricity rates during peak daytime hours and cheaper rates at night.In these cases, utilities such as Toronto Hydro recommend keeping your house cooler during off-peak hours. Haley said that couldlet your housestore the "coolness" like a thermal battery, possibly for much of the day, if it's well shaded and insulated.

Many utilities also suggest raising the thermostat when you're away from home. Bolger recommends against adjusting your thermostat more than a few degrees regularly, as that can force your equipment to work too hard to adjust to the change.

So with all that info, how do you choose the right temperature?

Bolger puts it this way: "There always has to be a balance between operation cost savings, efficiency and creature comfort."