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Start by blocking sun, limiting indoor heat, and cooling your body. Close shades or drapes on sunny windows, avoid using the stove or oven during the hottest part of the day, and open windows only when outdoor air is cooler and reasonably dry and clean. Use a fan only while the indoor temperature is below 90°F; the Centers for Disease Control and Prevention (CDC) warns that above 90°F a fan can increase body temperature.
These steps may improve comfort, but they cannot guarantee a safe indoor temperature during an extreme heat event. Drink water, use cool showers or wet cloths, check on people at higher risk, and move to an air-conditioned public place or cooling center if your home remains dangerously hot.
What to do first when a heat wave starts
- Measure the room. Put a digital indoor thermometer in the room where people spend time. It helps you determine whether the room is below the CDC fan-use threshold and shows whether conditions are worsening.
- Stop direct sunlight. Close blinds, shades, or drapes on windows receiving sun. Keep them closed through the hottest, brightest period rather than opening them for daylight.
- Reduce heat-making activities. Delay baking, roasting, and stovetop cooking. Prepare food that does not require an oven, or use appliances that add less heat to the room.
- Decide whether ventilation can help. Compare outdoor and indoor conditions before opening windows. If outside air is hotter, more humid, smoky, or otherwise unhealthy, keep windows closed and shaded.
- Protect people, not just rooms. Drink water regularly, cool your skin, and move anyone who feels unwell to a cooler location.
Use local weather and air-quality information when making the window decision. A heat wave with clean, cooler nighttime air is different from a hot, humid event or a smoke episode.
Block heat coming through windows
Sunlight through glass is a direct indoor heat source. Ready.gov recommends covering windows with drapes or shades when preparing for extreme heat, and the National Weather Service (NWS) also lists window coverings among its heat precautions. See Ready.gov’s Extreme Heat guidance and the NWS Excessive Heat preparedness page.
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Use the coverings you already have
- Close blinds, shades, or curtains on sun-facing windows before direct sun reaches the glass.
- Keep the coverings closed during the hottest part of the day, even if the room feels comfortable at first.
- Cover windows in rooms that are not occupied as well; heat stored in those rooms can spread through the home.
Short-term versus longer-term shade
Interior drapes and shades are immediate measures. Exterior awnings, shutters, or other permanent shading can reduce future solar gain, but they are not a substitute for a safe location during an active, severe heat event. Do not delay relocating because a home-shading project is unfinished.
When opening windows helps—and when it makes things worse
Window ventilation works only when the air outside can remove heat from the building. The U.S. Department of Energy explains that ventilation is not an effective cooling strategy in hot, humid climates. Its Home Cooling guidance supports treating ventilation as a condition-dependent choice, not a universal heat-wave rule.
Open windows when all of these conditions favor it
- Outdoor air is cooler than the indoor air you are trying to replace.
- Humidity is low enough that the air will not make occupants feel hotter or prevent sweat from evaporating.
- Outdoor air quality is acceptable, with no smoke, heavy pollution, or other local warning.
- The building can get useful cross-ventilation without creating a security risk.
Keep windows closed when conditions are unfavorable
- Outside temperature is higher than inside.
- Outdoor humidity is high and the air feels oppressive.
- Air-quality alerts, wildfire smoke, or other pollutants are present.
- Opening windows would expose occupants to unsafe weather or security hazards.
There is no single safe opening schedule for every home. Check conditions each time, especially as a heat wave changes from afternoon to evening. Close windows again when the outside air becomes hotter than the indoor air.
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A window that helped in the early morning may make the room hotter by midday. Recheck the thermometer and local conditions instead of relying on a routine copied from another home. Compare the indoor reading with the outdoor temperature, humidity, and air-quality information.
- If indoor temperature is below 90°F: A fan may provide comfort, provided the room is not becoming hotter and people continue to drink and cool themselves.
- If indoor temperature is at or above 90°F: Do not use a fan as the answer. Move people to a cooler room or begin arranging a cooler destination.
- If outdoor air is cooler, reasonably dry, and clean: Open windows briefly or create cross-ventilation if the building layout and security allow it.
- If outdoor air is hotter, humid, smoky, or polluted: Close windows, keep shades in place, and focus on cooling people directly.
This check prevents a common mistake: treating “fresh air” or moving air as automatically cooling. Ventilation and fans are tools whose value depends on actual conditions.
Use fans within the safety limit
The CDC’s current guidance is specific: "Use fans, but only if indoor temperatures are less than 90°F. In temperatures above 90°F, a fan can increase body temperature." This statement appears in About Heat and Your Health, dated July 20, 2026.
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What a fan can and cannot do
Below 90°F indoors, moving air can make a person feel more comfortable by increasing evaporation from the skin. A fan does not remove the room’s heat by itself; it mainly changes how the air feels around your body. If the room is above 90°F, follow the CDC warning rather than using a fan as a heat-safety solution.
The CDC also says not to rely solely on fans. A fan may provide comfort, but it will not prevent heat-related illness in very hot conditions. If the room is approaching or above the threshold, shift from comfort measures to cooling your body and finding a cooler place.
Check the temperature instead of guessing
A digital indoor thermometer is a task-enabling item, not a cooling device. Place it near the living area, away from direct sun, cooking appliances, windows, and fan airflow. Recheck it as the day progresses so your fan decision is based on the actual indoor temperature.
Cool your body directly
When the building cannot shed enough heat, cooling the person is faster than trying to lower every room. The CDC recommends drinking more water than usual without waiting for thirst and taking cool showers or baths. Its guidance for people without air conditioning is available at Heat and People without Air Conditioning.
Water and fluids
- Drink water regularly, even if you do not yet feel thirsty.
- Keep a bottle or glass within reach so drinking does not depend on remembering later.
- Follow medical advice if you have a condition that limits fluids or affects salt balance; do not make a major fluid change without guidance from your clinician.
Showers, baths, and wet cloths
- Take a cool shower or bath when you feel overheated.
- Apply cool, wet cloths to the skin and replace them as they warm.
- Move to the coolest available room while your body cools; do not return to the hottest room immediately.
The NWS advises moving a person with heat-exhaustion symptoms to a cooler environment and applying cool, wet cloths. Its Excessive Heat preparedness information describes these first steps.
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Use several personal-cooling steps at once while arranging help: stop exertion, drink water if you can safely do so, take a cool shower or bath, apply cool wet cloths, and move to the coolest available room. Ask another person to check on you rather than assuming that temporary relief means the danger has passed. If symptoms continue or worsen, seek medical care.
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Reduce heat generated inside the home
Every appliance that turns electricity or fuel into heat adds to the indoor load. Ready.gov specifically recommends using the oven less during extreme heat. Limit the largest avoidable sources during the hottest hours.
Cooking
- Use no-cook meals when practical.
- Prepare food earlier in the day, before indoor temperatures peak.
- Use a microwave or another appliance that heats the room less than an oven when appropriate.
- Keep the kitchen door closed if cooking is unavoidable and ventilate only when outdoor conditions support it.
Lighting, electronics, and laundry
Turn off unnecessary lights and electronics that produce noticeable warmth. Postpone heat-producing laundry cycles until a cooler period if doing so does not create a safety or sanitation problem. These steps reduce added heat; they do not replace hydration, body cooling, or leaving for a cooler location.
Choose the right measure for the conditions
| Measure | Primary effect | Depends on outdoor conditions | Electricity needed | How quickly it can help | Safety role |
|---|---|---|---|---|---|
| Shades, blinds, or drapes | Blocks incoming sunlight | No, once installed | No | Immediately after covering sunny windows | Reduces heat gain; does not guarantee a safe room |
| Opening windows | Replaces indoor air with outdoor air | Yes: temperature, humidity, air quality, and building layout | No | Potentially quick when outside air is cooler | Helpful only under favorable conditions |
| Fan | Moves air across the body | Indoor temperature determines whether CDC guidance allows use | Usually yes | Comfort can improve quickly below 90°F indoors | CDC says use only below 90°F and do not rely on it alone |
| Cool shower, bath, or wet cloths | Cools the person directly | No, though water access is required | No | Often faster for personal relief than cooling a room | Useful for heat discomfort and exhaustion while arranging further help |
| Air-conditioned public place | Moves the person into a cooler environment | Availability, travel, and facility hours vary locally | No household electricity required | As soon as you can safely get there | CDC-recommended option when the home is too hot |
Know when home cooling is no longer enough
Passive measures and fans cannot make every home safe during extreme heat. The CDC recommends spending time in an air-conditioned place such as a library, mall, or shelter; even a few hours can help. The agency’s guidance for people without air conditioning also advises finding air conditioning when needed.
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Plan a cooler destination before the house becomes unbearable
- Identify nearby air-conditioned public places you can reach safely.
- Check opening hours, transportation, accessibility, and any local entry rules before leaving.
- Contact local health or emergency-management agencies for cooling-center locations.
- Check local heat-risk and air-quality alerts before traveling and take water with you.
Cooling-center locations and hours vary by place and date, so verify them locally rather than relying on an old list. In the United States, local agencies may also direct residents to community information services; availability differs by jurisdiction.
Leave earlier if travel or mobility is difficult
People who live alone, have limited mobility, lack reliable transportation, or need medical equipment should make a departure plan before symptoms begin. Ask a trusted person to check in and arrange transportation while conditions are still manageable. Do not wait until confusion, severe weakness, or fainting makes travel dangerous.
Protect people at higher risk
Heat can worsen chronic health problems. The CDC specifically highlights pregnancy, asthma in children or teens, heart conditions, and other chronic conditions as situations in which heat may create additional risk. Older adults, infants, people taking heat-sensitive medicines, and anyone who lives alone may also need a more deliberate check-in plan; ask a clinician or local health department for advice tailored to the person.
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Make check-ins concrete
- Call or visit family, friends, and neighbors who live alone or have chronic medical problems.
- Ask what their indoor temperature is, whether they have water, and where they can go if the home heats up.
- Confirm that they can recognize symptoms and summon help.
- Do not assume a person is safe because a fan is running; the CDC says fans are not sufficient alone in very hot conditions.
The CDC’s prevention guidance includes checking on relatives, friends, and neighbors, especially those with chronic medical problems or who live alone. Read About Heat and Your Health for the current recommendations.
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Common mistakes to avoid
- Opening windows by habit: A nighttime routine is not automatically safe. Check whether the outside air is actually cooler, less humid, and clean.
- Using a fan because the room feels stagnant: Measure the indoor temperature first. Above 90°F, CDC guidance warns that a fan can increase body temperature.
- Waiting until thirst or severe symptoms: Drink regularly and start body-cooling measures early.
- Trying to cool the whole house before cooling a person: A cool shower, bath, or wet cloths can help the body more directly.
- Assuming one intervention is enough: Shade, less cooking, conditional ventilation, hydration, and a destination plan work as layers, not guarantees.
- Delaying a move to air conditioning: If the home remains dangerously hot, leave for a verified cooler place before confusion, fainting, or severe weakness makes travel harder.
Recognize heat illness and get help
Heat-related symptoms require prompt attention. The CDC lists muscle cramps, headaches, nausea, and vomiting among symptoms for which you should seek medical care immediately. Stop activity, move the person to a cooler environment, and begin gentle cooling while arranging medical advice.
Suspected heat stroke is an emergency
The NWS describes heat stroke as an emergency requiring immediate 911 or hospital care. Call emergency services for suspected heat stroke, especially when a person is confused, has an altered mental state, collapses, has a seizure, or cannot safely drink. Do not make the person travel alone or delay the call while trying additional home remedies. Follow the dispatcher’s instructions and continue cooling efforts that do not delay emergency care.
For a broader symptom and response reference, use the NWS Excessive Heat preparedness page and the CDC’s heat-prevention guidance.
A repeatable plan for the next hot day
- Before sunrise or early morning: Check the forecast, heat alerts, and air quality. Close sunny-window coverings before direct sunlight enters.
- During the morning: Prepare food that will not heat the kitchen later. Fill water containers and place a thermometer in the main living area.
- As outdoor temperatures rise: Keep windows closed if outside is hotter, more humid, or less healthy than indoors. Turn off unnecessary heat-producing devices.
- While indoors: Use a fan only when the indoor temperature is below 90°F, and pair it with regular drinking and body-cooling measures.
- At the first sign the home is too hot: Take a cool shower or bath, apply wet cloths, and move to a cooler room.
- Before symptoms escalate: Go to a verified air-conditioned public place or cooling center. Arrange help for anyone who cannot travel safely alone.
- For any serious symptoms: Seek immediate medical care; call 911 for suspected heat stroke.
The safest strategy is layered: prevent sunlight and appliance heat, ventilate only when conditions support it, use fans within the CDC limit, cool the body directly, and leave for air conditioning when the home cannot stay safe.
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Should I open windows when it is hotter outside?
No. Keep windows closed and shaded when outside air is hotter, very humid, smoky, polluted, or otherwise unsafe. Open them only when outdoor air is cooler than indoors, reasonably dry, and clean enough to improve conditions.
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Do fans help when the room is over 90°F?
The CDC says to use fans indoors only when temperatures are below 90°F. Above 90°F, a fan can increase body temperature, and it should not be treated as protection from heat illness. Move to a cooler place and cool your body directly instead.
What is the fastest way to cool myself without air conditioning?
Drink water regularly, take a cool shower or bath, apply cool wet cloths, and move to the coolest available room. If the home remains dangerously hot, spend time in an air-conditioned library, mall, shelter, or cooling center.
How do I know when to leave my home?
Leave when indoor conditions remain dangerously hot despite shade, reduced heat sources, and appropriate ventilation, or when someone feels unwell. Plan transportation and check facility hours before conditions become severe.
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Who should receive extra check-ins during a heat wave?
Check on people who live alone or have chronic medical problems. The CDC specifically identifies pregnancy, asthma in children or teens, heart conditions, and other chronic conditions as situations in which heat can worsen health.
Which heat symptoms require urgent help?
Muscle cramps, headache, nausea, and vomiting warrant prompt medical care. Confusion, altered mental state, collapse, seizure, or inability to drink may indicate heat stroke; call 911 or your local emergency number immediately.
Is a digital indoor thermometer worth using?
It can help you check the room against the CDC’s 90°F fan-use threshold and notice worsening conditions. Keep it out of direct sun, away from cooking appliances, windows, and fan airflow. It measures conditions but does not cool the room or prevent illness.
The Bottom Line
Shade sunny windows, limit oven and stove use, and open windows only when outdoor conditions are genuinely better. Use fans only below 90°F indoors, cool your body with water and cool showers, and do not rely on passive steps alone during extreme heat.
If the home stays dangerously hot, go to a verified air-conditioned public place or cooling center. Check on people at higher risk, and seek immediate help for serious symptoms or suspected heat stroke.
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