What temperature should I set my AC to in Phoenix? How to stay cool, safe during the summer

Laura Daniella Sepulveda, Arizona Republic
·6 min read
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Phoenix's soaring temperatures have been breaking all-time records, causing at least 25 confirmed deaths so far this year, taking a toll on the city's unhoused population, killing band equipment at concerts and impacting outdoor workers.

It doesn't come as a surprise that for many living in the hottest large city in the U.S., air conditioning is not so much of a luxury as it is a need. According to an analysis published by the U.S. Energy Information Administration in May, more than nine in 10 homes in Arizona rely on air conditioning usage, consuming more electricity than the residential sectors in three-fourths of the states and more per capita than seven-tenths of the states.

In 2022, nearly half of Arizona's electricity sales went to the residential sector, according to the report. Most residents of the Valley find it hard to imagine what their daily lives would be like without AC.

Here's what you need to know about this essential cooling tool, and how you should use it in Arizona.

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Who invented air conditioning?

According to the U.S. Department of Energy, the idea started with John Gorrie, an 1840s inventor from Florida who believed cooling cities would help avoid diseases like malaria.

His first cooling systems relied on transporting ice from frozen lakes into the humid state, which was later realized as not too efficient. Gorrie then started experimenting with artificial cooling, which laid the foundation for modern AC.

About half a century later, an engineer named Willis Carrier was asked to solve a humidity problem at a Brooklyn publishing company that was causing magazine pages to wrinkle. So, he designed a system based on cooling coils that controlled humidity by heating or cooling water. He called it "Apparatus for Treating Air," and patented it.

Carrier's technology evolved into smaller and more affordable devices that could be installed at home, and by the end of the '60s, most newly built homes had central air conditioning, boosting population growth in hot states like Arizona.

What temperature should I set my AC to in Phoenix?

Brianna Callaway, a spokesperson with Valley Services, a Phoenix-based HVAC repair company, said residents should be able to set their AC at the temperature they feel most comfortable with. Yet, she recommended residents to keep it set at the same temperature when they are at home, and move it up or down as little as they can.

"I would say most people like to keep it around 75 degrees," Callaway said. "When you're gone, you could leave it around 79 or 80, but if you're at home, we recommend keeping it at the same temperature."

If you want to turn your AC down by one or two degrees on a particularly hot afternoon, it won't hurt, Callaway said, but keeping your AC at the same temperature will help you save energy during the hot summer months in Arizona.

What size AC unit do I need in Phoenix?

Callaway said it's hard to tell since it depends on various factors like your home size, how many windows you have, how the air flows through the rooms, etc.

To calculate your ideal AC unit size, Callway advised residents to get a Manual J Calculation, which is performed by air conditioning contractors.

"They would calculate based on the square footage of the house, the way the house is spacing, the windows of the house, and they could tell you exactly what you need," she said.

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Is it normal for AC to run all day in Arizona?

In the summer, yes, Callaway said. But not in other seasons.

If your AC runs all day during other times of the year, Callaway recommended having your AC checked by a professional.

How do I know when my AC needs replacing?

Some of the signs you should look out for include weird noises, or if your house is not cooling down to the temperature you want.

But the best way to keep track of when your unit needs replacing is by having it checked by a professional at least twice a year, Callaway said.

How long should an AC last in Phoenix?

Anywhere from 12 to 15 years would be normal, Callaway said.

To prolong the life of your AC unit to the maximum, Callaway recommends having your AC serviced on every six months, once in the spring and once in the fall.

"That way, the technician can keep track of the overall health of the unit," she said.

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What is the best time of year to replace an AC?

Callaway said the cooler months would be the best to replace your AC. That way, the new unit will gradually build cooling activity up as months get hotter in the first half of the year.

During the winter is also when air conditioning contractors are less busy and will be able to best fit people's schedules, Callaway said.

How much does a new AC cost?

Although there are many variables that affect AC unit pricing, Callaway said a typical medium-sized unit with a regular efficiency rating averages at around $10,000.

How can I conserve energy?

Callaway said using fiberglass filters and changing them every three to four weeks can help the AC run better and save energy.

Dana Marie Kennedy, Arizona director of The American Association of Retired Persons, also gave out some tips to save energy during the summer:

  • Close your blinds before leaving home during the day

  • Turn on your fans to help circulate the air

  • Wear light clothing to stay cool

  • Limit the use of high‐energy appliances during peak hours

  • Switch off lights and unplug appliances when not in use

  • If possible, invest in smart thermostats and energy‐efficient appliances

How can elderly people stay safe in the heat?

Every year, Phoenix's heat weighs on older adults, who are more susceptible to heat-related symptoms and illnesses. A recent report from the Maricopa County Department of Public Health showed that about a third of the heat-associated deaths that have been confirmed in 2023 so far were people aged 75 years or older.

AARP has a number of senior centers across Valley neighborhoods including Paradise Valley, Sunnyslope, Shadow Mountain and Deer Valley.

"They can stay cool there, they'll get a free meal, so that is definitely an option," Kennedy said.

She also reminded residents that power provider companies cannot cut off utilities due to late payment, non‐payment, or accumulated debt during extreme weather conditions.

Residents who are struggling with utility bill payments can apply for the Energy Assistance Program through APS or SRP.

A senior hotline is available for people who have any questions about resources for older citizens in Arizona. You can call the Area Agency on Aging's 24-hour helpline at 602-264-4357, or Arizona's general resource hotline 2-1-1.

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This article originally appeared on Arizona Republic: AC in Phoenix: Your guide to air conditioning maintenance and settings