When the Grid Can't Keep Up: Heat Waves and Your Sleep

Quick answer: during major summer heat waves, grid operators are increasingly issuing emergency conservation appeals and, in some cases, ordering rolling blackouts or curtailing large power users to avoid a wider grid failure. If that happens overnight, you can lose air conditioning at exactly the hours your body most needs it to cool down and sleep. This isn’t a rare event anymore: 2026 has already seen multiple grid emergency declarations, including a May 2026 DOE order allowing one major grid operator to curtail data centers as “a last resort before instituting rolling blackouts.” Knowing this can happen, and having a plan before it does, matters more than most people realize.

Who This Is For

You live somewhere your utility or grid operator has issued a conservation appeal or flex-alert asking people to raise their thermostat overnight
You’ve experienced, or are worried about, a rolling blackout or planned outage during a heat wave
You want to understand whether running a fan is actually enough once the AC goes out, or whether that’s dangerous advice at a certain temperature
You’re responsible for someone more vulnerable to heat (an older relative, a young child, someone with a chronic health condition) and want a real plan, not just “stay hydrated”
You’ve noticed nights not cooling down the way they used to and want to understand why that specifically hurts sleep

Quick Fix / Summary

Sign up for your utility’s outage and conservation alerts before a heat wave hits, not during one, so you have advance warning rather than finding out when the power drops
Do not rely on a fan alone in extreme heat: the CDC, EPA and WHO advise against relying on fans once temperatures reach the mid-90s °F, and some research suggests fans can raise heart rate and core temperature in older adults in dry heat
Pre-cool your bedroom and your body before a known outage window: lower the thermostat a few extra degrees in the hours before an anticipated evening peak, and consider a cool shower right before bed
Have a non-electric backup cooling plan ready (a battery-powered fan, cooling towels, a plan for where you’d go if your home becomes unsafe) rather than improvising after the power is already out
Check on anyone in your household or nearby who is older, very young, pregnant, or managing a chronic condition; they’re at meaningfully higher risk during an overnight outage in extreme heat
If your home becomes unsafe to sleep in during an outage, treat that as a real decision point (a cooling center, a friend’s house, a hotel), not something to tough out

Why This Happens

Summer grid emergencies are becoming a routine feature of heat waves, not a rare event

As electricity demand for air conditioning spikes during heat waves, and as growing loads like data centers add to overall demand, grid operators have had to lean on emergency measures more often. In 2026, PJM, the grid operator serving a large swath of the mid-Atlantic and Midwest, requested a Department of Energy emergency order on May 17 for a three-day window starting May 18, after projecting more than 40 gigawatts of generation offline for planned maintenance on May 18 combined with unseasonable heat, and expecting reserves to fall below 5,800 megawatts during that day’s peak. DOE issued the order on May 18. The resulting order let PJM curtail power to data centers and other large facilities with their own backup generation, a step the order itself describes as a last resort meant to prevent rolling blackouts, according to reporting from Utility Dive. That wasn’t an isolated event: a July 2026 heat wave triggered a separate DOE grid emergency declaration affecting roughly 160 million people across 30 states, with PJM forecasting record demand above 166,000 megawatts, according to weather.com’s coverage. Utilities across the affected region issued conservation appeals asking residents to set thermostats to 78°F during the day, with some, including Philadelphia’s PECO and Washington’s Pepco, specifically asking for 80°F overnight, precisely the hours sleep depends on cooler air. That same event saw forecast heat indices above 110°F and nighttime lows struggling to drop below 80°F, meaning the usual overnight relief homes count on wasn’t coming even before accounting for any power loss.

The pattern matters because it means residential power loss during a heat wave is no longer a freak occurrence tied to one storm or one failure. It’s an intentional tool grid operators reach for to prevent a larger, less controlled failure, and it’s being used more as demand keeps climbing.

Overnight heat, specifically, is what disrupts sleep the most

The body relies on nighttime cooling to fall and stay asleep: core temperature normally drops in the evening, and a bedroom that stays hot works directly against that process. A Climate Central data analysis reported by Scientific American found that people globally lost an estimated 56 hours of sleep per year between 2020 and 2025 due to high overnight temperatures, with some U.S. locations, including San Juan, Puerto Rico, losing closer to 85 hours a year, and desert cities like Flagstaff and Reno seeing roughly a 31 percent increase in heat-driven sleep loss since 1970. Urban climatologist Ariane Middel, quoted in that reporting, explains the mechanism simply: when daytime heat is followed by a warm night, the body has to keep working to cool itself instead of resting. For what the 56-hour figure means night by night, see Hot Nights and Lost Sleep: What 56 Hours a Year Means.

Losing air conditioning specifically overnight, during a grid emergency or planned outage, removes the one tool most people rely on to counter this, right at the hours it matters most.

Fans have real limits once temperatures climb high enough

A fan is the obvious fallback when the AC is out, but it isn’t a universal substitute, and treating it as one can be genuinely risky at high temperatures. A fan mainly works by moving air across the skin to help sweat evaporate, and once the air is hot enough that moving air may stop cooling you. According to weather.com’s report, the CDC, EPA, WHO and American Lung Association all advise against relying on fans once temperatures hit the mid-90s °F, and the EPA warns that electric fans will not prevent heat-related illness at that point. The evidence is not settled: the same report says a University of Sydney study found fans still helped people in hot, humid conditions, even at a heat index above 100°F, while JAMA Network Open research found that in dry heat a fan can increase heart rate and core body temperature, especially in older adults. Because the picture is mixed, the safe approach is to treat a fan as a comfort aid at best in extreme heat, and to move to air conditioning or an air-conditioned space away from home if temperatures are very high or anyone is vulnerable.

How to Fix It

Get ahead of it: sign up for alerts before the season’s first heat wave

Most utilities and regional grid operators (PJM, ERCOT, and others) publish conservation appeals and outage risk notices, and many let you sign up for text or email alerts. Doing this before a heat wave arrives, rather than searching for information after your power is already out, is the single biggest difference between reacting well and being caught off guard.

Pre-cool before a known risk window

If a conservation appeal or heat advisory names a specific evening window as the highest-risk period (a common pattern, since demand peaks are usually late afternoon into evening), lowering your thermostat a few extra degrees in the hours beforehand gives your home, and your body, more thermal buffer if the power does go out later. A cool shower shortly before bed can do the same thing for your body specifically, and doesn’t require any equipment.

Know when a fan helps and when it doesn’t

In moderate heat a fan can add comfort, but once temperatures reach the mid-90s °F, official guidance is not to rely on one. A fan is not a reliable substitute for AC in extreme heat and may work against you, particularly for older adults in dry heat. Don’t treat “I have a battery-powered fan ready” as a full outage plan for a severe heat wave; treat it as one part of a plan that also includes somewhere cooler to go if temperatures climb past that point.

Build a non-electric cooling kit before you need it

A battery- or hand-crank-powered fan, a supply of cooling towels or a way to keep a few in a cooler with ice, and a clear sense of your nearest cooling center or an air-conditioned location you could go to (a relative’s home, a store, a library) are worth having ready before the first outage of the season, not improvised during one.

Check on higher-risk people specifically

Older adults, infants and young children, pregnant people, and anyone managing a chronic health condition or taking certain medications are at meaningfully higher risk during an overnight outage in extreme heat, both because their bodies regulate temperature less effectively and because they may be less able to recognize or act on early warning signs themselves. If you know someone in one of these groups, checking in during a grid emergency or heat advisory is a genuinely protective action, not an overreaction.

Know your exit option

If your home becomes unsafe to sleep in during an extended outage, whether that’s an official cooling center, a friend or family member’s air-conditioned home, or a hotel, treat leaving as a legitimate, planned-for option rather than a last resort you only consider once things are already bad. Deciding this in advance, before you’re tired, hot, and trying to think clearly at 2 a.m., makes it much more likely you’ll actually act on it in time.

For the general tools that help you sleep cooler on any hot night

Beyond outage-specific preparation, the everyday tools that help with hot-weather sleep, cooling bedding, room setup, and nighttime routines, are covered in more depth in how to sleep cool during a heatwave without AC and how to stay cool while sleeping at night. Those pieces are the right place for day-to-day heat-sleep tips; this one is specifically about the added risk when the power itself is at risk during a grid emergency.

When to See a Doctor or Get Emergency Help

The NHS lists tiredness, dizziness, headache, nausea or vomiting, heavy sweating and pale, clammy skin as signs of heat exhaustion, and advises calling 111 if you cannot manage the symptoms yourself. Heatstroke is an emergency: signs include a very high temperature, hot skin without sweating, fast breathing and heartbeat, confusion, a seizure or loss of consciousness. Call emergency services (999 in the UK, 911 in the US) if someone has these signs or is still unwell after 30 minutes of resting in a cool place, being cooled and drinking fluids. Talk to a doctor in advance if you or a relative take regular medicines or have a long-term condition and want a heat plan.

Common Mistakes

Assuming a fan is always a safe AC substitute, when official guidance says not to rely on one once temperatures reach the mid-90s °F
Waiting until a heat wave is already underway to sign up for utility outage or conservation alerts
Having no non-electric backup plan and improvising for the first time during an actual outage
Not checking on higher-risk people (older adults, infants, those with chronic conditions) specifically during a grid emergency, assuming a general check-in is enough
Treating leaving home for a cooler location as a last resort instead of a planned option decided on ahead of time

FAQ

How common are these grid emergencies actually becoming?

More common than most people realize. In 2026 alone, a May DOE-approved emergency order let PJM curtail data centers and large facilities to avoid rolling blackouts, and a July 2026 heat wave triggered a separate DOE grid emergency declaration affecting roughly 160 million people across 30 states, with utilities in the Northeast Corridor issuing conservation appeals asking residents to raise their thermostats, including overnight.

Is it true that data centers get cut off before regular homes during a grid emergency?

In at least the May 2026 PJM case, yes: the emergency order specifically allowed curtailing data centers and other large facilities with their own backup generation as a step to avoid rolling blackouts affecting the wider grid, including homes. That’s not a guarantee for every future event or every grid operator, but it reflects how these emergency measures are generally structured, largest loads first.

At what temperature does a fan stop being helpful?

There is no single agreed cut-off. The CDC, EPA, WHO and American Lung Association advise against relying on fans once temperatures reach the mid-90s °F, while one University of Sydney study found fans still helped in hot, humid conditions. In dry heat, other research found a fan can raise heart rate and core temperature in older adults. In very hot weather, air conditioning or an air-conditioned space is the safer option.

What should I do differently if someone in my home is elderly or has a health condition?

Treat an overnight outage during extreme heat as a higher-stakes situation for that person specifically. Check on them more than once during the night if possible, know the early signs of heat-related illness, and have a lower threshold for moving them to a cooler location rather than waiting to see if things improve.

Key Takeaways

Grid emergencies, conservation appeals, and even planned curtailments during summer heat waves are becoming a routine part of the season, not a rare event, and losing air conditioning specifically overnight works directly against the body’s natural cooling process at the hours sleep needs it most. Fans have real limits: official guidance is not to rely on them once temperatures reach the mid-90s °F, and they may work against you in dry heat. The most effective response is preparation before a heat wave arrives: sign up for alerts, pre-cool your space, build a non-electric backup kit, check on higher-risk people specifically, and decide your exit option in advance rather than under pressure.

About this article

Written by the Sleep Fixes editorial team. We’re not medical professionals. We research each topic against primary sources and hold ourselves to being critical and thorough about what actually makes it onto the site.

This article is based on 2026 grid-operator emergency orders and reporting, published climate and sleep-loss data, and current research and public health guidance on fan safety during extreme heat. It is not medical advice. If you or someone in your household is showing signs of heat-related illness, seek medical attention rather than relying on this article.

When the Grid Can’t Keep Up: Heat Waves and Your Sleep