Why 78 degrees isn’t the right thermostat setting for everyone during a heat wave

Across the U.S., it’s a hot summer, and electricity prices are high. Various public officials and corporate websites suggest people set their thermostats to 78 degrees Fahrenheit (25.6 degrees Celsius), or even 81 F (27.2 C), as a way to stay relatively cool without breaking the bank. But as someone who studies energy costs, I know from both personal and professional experience that it’s not that simple.

The summer after my daughter’s first birthday, she began vomiting in the middle of the night and small bumps covered her chest. I thought it was the blueberries we’d given her. My husband and I cut out acidic foods and changed her milk. At the time, we often kept our thermostat set to 79 F (26.1 C). Before becoming parents, that setting kept the summer electric bill below US$200. We would sleep without blankets and take cold showers like I had in graduate school.

Then, on a cooler night, she kept her blueberries down. After that, I lowered the hallway thermostat setting enough to get her bedroom near 74 F (23.3 C). The nighttime vomiting stopped. My experience as a parent changed how I hear universal recommendations for air conditioner settings, especially during heat waves.

There is no single thermostat setting that is right for every person or every home. And there are other easy, low-cost steps that can help keep everyone comfortable when hot weather sets in.

Air conditioning is a big help, but can be costly

Every piece of cooling equipment is different, in terms of its technical design specifications, and its age and maintenance history. And the homes these systems serve vary in terms of insulation, size, sun exposure, and local climate. So there’s not one temperature setting that’s maximally energy- and cost-efficient for every home.

It may be useful to start at 78 F (25.6 C) to keep a lid on costs, but that temperature is neither a safety threshold nor a temperature every household will find comfortable and safe. If you are uncomfortable, try lowering your thermostat one degree at a time while monitoring yourself and others in your household for any signs of heat stress.

In general, a higher thermostat setting saves energy because the air conditioner has less work to do. When it is 95 F (35 C) outside, maintaining a home at 78 F requires removing less heat than maintaining it at the average level most U.S. households seek in the summer: 72 F (22.2 C). The smaller the difference between the indoor and outdoor temperatures, the less frequently or intensely the air conditioning system has to run, thereby using less electricity.

Running an air conditioner also reduces the humidity in a home. When the air is humid, sweat evaporates less effectively. The National Weather Service has a chart that says if the temperature is above 90 F (32.2 C), and the humidity is above 60%, the air will feel like it’s above 100 F (37.8 C).

Running air conditioning may be necessary in a heat wave, but it can represent over 50% of a home’s energy usage in summer months – and a similar proportion of the resulting electricity bill.

Fortunately, there are other ways you can keep yourself and your home cool for very little money.

Keep heat out

Prevent outside heat from seeping into the building by closing curtains on sun-facing windows. Close windows and doors too, unless it is cooler outside than inside, which may happen overnight or in the early morning.

And don’t add more heat inside your home if you can avoid it. For instance, avoid using the oven during the hottest part of the day.

Combine air conditioning with air movement

The moving air from a ceiling fan or a portable fan can make temperatures feel cooler, even if the thermostat is set relatively high.

But the Centers for Disease Control and Prevention say people should only use fans to cool themselves down when indoor temperatures are below 90 F (32.2 C). This is because when the air is hotter than your skin temperature – about 90 to 94 F – a fan creates a convection oven effect, accelerating the shift of heat into the body and potentially raising your body temperature to unhealthy levels.

The thermostat isn’t in every room

Remember that a hallway thermostat may not reflect the temperature in an upstairs room, or one facing the sun. Use an inexpensive thermometer to measure temperatures in the rooms where people actually sleep or spend their time. If possible, have people stay in shaded rooms or on a lower floor, or even in one space, rather than cooling every room equally.

Cool your body as well as the rooms

A cool shower or a damp cloth can provide immediate relief, and drinking water regularly helps replace fluid lost through sweating. If you are feeling really hot, consider using ice packs to help cool your body down.

Always protect your health

There are many stories of people dying indoors because they turned off their working air conditioners during times of high heat, or because their cooling system wasn’t functioning properly.

Infants and people with certain health conditions may need to be in cooler spaces for longer periods of time than healthy adults.

Don’t be afraid to seek help

If your home’s heat makes you afraid for your health, call your local 211 resident-services hotline or search online for local cooling centers where you can spend some time in air conditioning at no charge. Even a few hours in an air-conditioned space can reduce heat risk. Splash pads and public pools are other options, as are public libraries and other government buildings, or even a restaurant, cafe or movie theater, which often have air conditioning.

Keep an eye on yourself and each other for signs of heat stress. If someone becomes dizzy, weak, intensely thirsty, nauseated, confused or unusually tired, move them to a cooler place or go to the hospital. Confusion, loss of consciousness and very high body temperature can indicate heat stroke, which is a medical emergency.

Lastly, if you need help paying your electricity bills, check in with your utility company, which may have programs for spreading out your costs over time. You may even find you’re eligible for cost subsidies. State and local governments also usually have programs that help residents insulate their homes and upgrade inefficient appliances.

The best temperature setting is the one that provides adequate cooling at costs the household can sustain. While a thermostat setting of 78 F (25.6 C) is often touted as a solution, in reality it is just one of several options. In my house, becoming a mother changed the amount I determined was necessary to spend on my summer cooling bills. I couldn’t determine the right amount of cooling from the thermostat or my electricity bill – I had to look after the people in my home.