How to stay safe in extreme heat
Heat is the deadliest weather hazard in the United States — deadlier than floods, hurricanes and tornadoes combined — and the single most misunderstood piece is the electric fan: above the mid-90s °F, a fan can make heat stress worse, not better. This guide sticks to what the NWS, EPA, CDC and OSHA actually say, with every figure sourced.
First, check where you stand right now
“How hot does it feel” isn’t the air temperature — it’s the heat index, which combines temperature and humidity. Run the National Weather Service’s own formula for your conditions, and see whether a fan or evaporative cooler will even help:
What the heat-index numbers mean
The National Weather Service sorts the “feels-like” heat index into four bands of rising risk. Note how fast humidity stacks the deck: at 100 °F, dry 15 % air feels like 96 °F, but humid 55 % air feels like 124 °F.
| Heat index | NWS band | What it means |
|---|---|---|
| 80–90 °F | Caution | Fatigue possible with prolonged exposure and/or physical activity. |
| 90–103 °F | Extreme Caution | Heat stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or physical activity. |
| 103–124 °F | Danger | Heat cramps or heat exhaustion likely, and heat stroke possible with prolonged exposure and/or physical activity. |
| 125 °F + | Extreme Danger | Heat stroke highly likely. |
Source: NWS heat index chart. Worked examples are the NWS’s own.
The fan trap: when moving air stops helping
A fan cools you by evaporating sweat. Once the air is hot enough, it stops doing that and simply blows hot air across your skin — like a convection oven. The EPA is blunt about it:
“Do not use electric fans for cooling when the room temperature is in the mid-90s or higher. When it is that hot, electric fans will not prevent heat-related illness.”— US EPA, Extreme Heat and Indoor Air Quality
The federal Excessive Heat Events Guidebook puts a number on it: fans are useful while the heat index is below the high 90s, but using a fan alone once the heat index passes about 99 °F can actually increase heat stress. Above that threshold the honest answer isn’t a better fan — it’s air conditioning, or getting to somewhere that has it. (For reference, heat stroke sets in when core body temperature reaches about 106 °F.)
If your room is in the mid-90s and you have no AC, a fan is not enough. Get to a cooling center, mall, library or any air-conditioned building — the EPA lists these as the standard fallback when home cooling isn’t available.
What actually keeps a home cooler
- Work the windows like a valve. Close windows and shades when it’s hotter outside than in; open them when it’s cooler outside, especially overnight; and shade the sun-facing windows during the day. (EPA)
- Set the thermostat with intent. ENERGY STAR’s cooling guide suggests roughly 78 °F while you’re awake and home, letting it drift up at least 7 °F when you’re away and about 4 °F warmer while you sleep. Nudging the thermostat up 2 °F and running a ceiling fan can “lower your air conditioning costs by up to 14 %.”
- Hydrate before you’re thirsty. OSHA’s guidance for people working in heat: for short tasks water is enough; for anything beyond about two hours, add an electrolyte beverage — and don’t wait until you feel thirsty to start drinking.
Who is most at risk
Heat doesn’t hit everyone equally. The CDC flags these groups as the most vulnerable — check on them during a heatwave, and don’t assume a healthy adult is immune during exertion:
- Adults 65 and older
- Infants and young children
- People with chronic conditions (heart disease, diabetes, mental illness and others)
- People without access to air conditioning
- Athletes and outdoor workers
- Pregnant people
Why this matters: in 2024, heat killed 529 people in the US — more than flash floods (119), hurricanes (78), tornadoes (52) and cold (46). It is the deadliest weather hazard in the country, and nearly all of those deaths are preventable with shade, water, and getting somewhere cool in time.
Source: NWS 2024 weather fatality summary.
Why the next two summers could break records
El Niño 2026–27 · monthly tracker A developing El Niño is the early warning that summer 2027 could set heat records El Niño is a warm Pacific-Ocean pattern — think of it as a fever in the ocean that runs hottest in winter — and it’s the single biggest driver of record global heat. The catch is the lag: the hottest years on record tend to land the year after it peaks. We track the official NOAA data monthly (latest ONI +0.98, El Niño Advisory as of 2026-07-05) and explain, in plain language, what it does and doesn’t mean for your summer. →Questions people actually ask
At what temperature does a fan stop cooling you down?
What heat index is considered dangerous?
What should I set my thermostat to in summer?
How much water should I drink in extreme heat?
I don’t have air conditioning — what do I do during a heatwave?
Keep reading
- El Niño 2026–27 tracker — the latest official NOAA numbers (updated monthly) and an honest read of what the developing El Niño does and doesn’t mean.
- Cooling gear guides — if a fan isn’t enough where you live, the honest guides to portable ACs, window units and tower fans. An evaporative cooler only helps in dry air — the checker above tells you if that’s you.