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The safest heatwave strategy is to keep heat out during the day, ventilate only when outdoor air is cooler after dark, and measure indoor temperature at set checkpoints. Shade sunny windows, switch off unnecessary heat-producing equipment, and use the coolest room for sleeping. Use a fan only while indoor temperature is below 90°F (32.2°C); above that, do not rely on it to prevent heat illness. If your home cannot stay reasonably cool, move to air conditioning or a designated cool public place, especially when infants, older adults, people with chronic illness, people with disabilities, or anyone living alone is at risk.
Make a heatwave plan before the hottest hours
Preparation is more effective than trying to cool a fully heated home. Before temperatures rise, decide who will check on vulnerable people, where everyone can go if the power fails, and how you will monitor the indoor environment. Write down phone numbers, transport options and the address of your backup location so nobody has to make decisions while overheated.
Check cooling equipment and backup locations
- Test central or room air conditioning before the heatwave. Confirm that controls, filters, electrical connections, and any required condensate drainage work as the manufacturer specifies.
- Choose a backup location with dependable air conditioning: a public library, shopping mall, cooling center, public building, or trusted friend’s home. Note its opening hours, accessibility, pet policy and how you will get there.
- Put phones, backup batteries, prescription medicines, and essential power supplies for medical devices where you can reach them quickly during an outage. Charge batteries before the hottest period.
- Place a readable indoor room thermometer in the main living area and another near the bedroom if possible. Avoid positioning one directly beside a window, cooker, lamp, radiator, or air-conditioning outlet.
- Decide which room is likely to remain coolest and move bedding, water, medicines and seating there before the heat peaks.
Prepare windows and people
- Identify windows that receive morning or afternoon sun. Have blackout or thermal shades, blinds, or shutters ready to close before direct sunlight enters.
- List people who need regular checks: adults over 65, infants, anyone with heart, lung, kidney, or other chronic disease, people with disabilities, and neighbors who live alone.
- Include pets in the plan. Arrange water, a cooler room, and a way to transport them if the household must leave for an air-conditioned place.
- Check local heat alerts and transportation information. A cooling center is useful only if you can reach it safely and during its operating hours.
Measure indoor temperature and know when to escalate
Feeling hot is not a reliable measurement. The World Health Organization (WHO) advises checking indoor temperature at three daily checkpoints: 08:00–10:00, 13:00, and after 22:00. Record the reading and whether the thermometer is in the main occupied room or bedroom. A simple written log shows whether overnight ventilation worked and whether the building is accumulating heat each day.
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|---|---|---|
| 08:00–10:00 | Record the overnight result and decide whether extra shading or an earlier move to a cool place is needed. | Keep daytime temperature below 32°C (89.6°F). |
| 13:00 | Check the hottest part of the day before deciding whether the home remains suitable. | Keep daytime temperature below 32°C (89.6°F). |
| After 22:00 | Check whether the building has released enough heat for sleeping and whether outside air is now cooler. | Keep nighttime temperature below 24°C (75.2°F). |
These are WHO indoor targets for heat protection, not a universal medical cutoff. A room that stays above them warrants earlier action, such as moving to air conditioning, particularly for someone medically vulnerable. Do not wait for a thermometer reading if a person develops dangerous symptoms. A thermometer also helps compare rooms: move people to the coolest measured room rather than relying on assumptions about which room feels cooler.
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Use the readings to make a decision
- If outdoor air is hotter than the room, keep windows closed and concentrate on shade and reducing indoor heat.
- If outdoor air becomes cooler after dark, ventilate safely until the outside temperature starts rising above the indoor reading.
- If the home remains above the daytime target, or a vulnerable person cannot sleep in a room below the nighttime target, arrange several hours in an air-conditioned location.
- If anyone shows confusion, fainting, loss of consciousness, delirium, severe dizziness, or worsening nausea, treat it as a medical emergency rather than a household-cooling problem.
Keep daytime heat and sunlight out
Close openings when outside is hotter
During the day, shut windows and exterior doors whenever outdoor air is warmer than indoor air. Opening a window does not cool a room when the incoming air is hotter; it adds heat. Close windows again in the morning before outside temperatures overtake the indoor reading. This rule applies even if a breeze feels pleasant: compare temperatures rather than judging by airflow alone.
Block direct solar gain
Close blinds, shutters, or blackout and thermal shades on sun-facing glass before sunlight reaches the room. Keep the covering closed through the hottest period. A light curtain alone may not block as much radiation as a tightly fitted blackout or thermal shade, so use the most effective covering available for each exposed window. Recheck rooms as the sun moves; a window that is shaded in the morning may need covering in the afternoon.
Stop making indoor heat
- Turn off lights, televisions, computers, chargers, and other electrical equipment that nobody needs. Put devices into sleep or power-off modes rather than leaving them running.
- Use the stove and oven as little as possible during the heat peak. Choose food that needs minimal cooking and avoid activities that warm the kitchen.
- Move household activity into the coolest room. If one room is consistently cooler, keep its door closed when practical and use it for resting or sleeping.
- Plan errands, laundry and other heat-producing tasks for cooler hours when possible, and avoid opening the oven repeatedly.
Ventilate overnight without losing the advantage
After dark, open windows only when the outdoor temperature is lower than the indoor temperature and doing so is safe for your household. The cooler air can replace air that warmed during the day. Continue checking the thermometer rather than leaving windows open by habit.
- After 22:00, compare the indoor reading with the outdoor temperature or a reliable local reading.
- Open windows if outside is cooler and there is no safety, smoke, storm, or other local reason to keep them shut.
- Close them before morning heating makes outdoor air warmer than the room.
- Reapply blinds or shades as soon as direct sun reaches the glass.
Night ventilation is a temperature-dependent action, not a fixed schedule. On a hot night when outside never becomes cooler, keep windows closed and use air conditioning or relocate instead. If outdoor air quality, wildfire smoke or severe weather makes opening windows unsafe, skip ventilation and use the planned cool location.
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Use fans only within safe temperature limits
Fans move air across skin; they do not remove heat from a room. Their safety depends on the indoor temperature and the person’s condition.
| Indoor condition | Fan guidance | Safer choice |
|---|---|---|
| Below 90°F (32.2°C) | The Centers for Disease Control and Prevention (CDC, 2026) says fans may be used below this temperature. | Use a fan for comfort while continuing to monitor the thermometer and the person. |
| 90°F (32.2°C) or higher | CDC warns that a fan can increase body temperature at these temperatures. | Do not depend on a fan alone; move to air conditioning or a cooler public place. |
| Above 35°C (95°F) | WHO (2024) says an electric fan may not prevent heat-related illness and can heat the body above 40°C (104°F). | Stop treating the fan as protection and escalate cooling immediately. |
The 90°F and 35°C figures are not contradictory promises of safety: they are warnings that benefit declines as heat rises. A fan can still be useful in an air-conditioned room. WHO advises setting air conditioning to 27°C (81°F) and using an electric fan; it says the combination can make the room feel about 4°C cooler. Keep doors and windows closed while air conditioning is operating so cooled air is not replaced by hotter outside air.
Fan placement and household checks
- Use the fan to provide personal comfort in a room that is below the CDC limit, not as a substitute for air conditioning during extreme heat.
- Check older adults, infants, and people with chronic illness directly; they may not recognize or communicate dangerous overheating.
- If someone becomes confused, faint, severely dizzy, or progressively nauseated, turn attention to emergency care rather than increasing fan speed.
- Stop using a fan as the main strategy when the indoor reading reaches 90°F (32.2°C), even if moving air still feels comfortable.
Air-conditioning safety and efficient operation
When air conditioning is available, set it to 27°C (81°F) as the WHO’s cited guidance and add a fan only when the room is below the CDC fan limit. Keep doors and windows closed during operation. Follow the appliance manufacturer’s electrical, ventilation, drainage, and installation instructions; do not overload outlets or improvise exhaust arrangements.
Homes without central air conditioning
A properly installed portable air conditioner can cool an occupied room, but it must be used exactly as its manufacturer specifies, including electrical load, exhaust routing, and condensate handling. Close the room’s windows and doors while it runs. Prioritize the room where people sleep or where a vulnerable person spends time, and keep the thermometer there. Compare a portable unit with passive measures realistically: shades and closed windows reduce heat entering, while air conditioning actively lowers room temperature and is the more dependable choice when targets cannot be met.
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When air conditioning or power fails
The American Red Cross advises not relying only on electric fans during extreme heat. If electricity is unavailable or cooling equipment cannot keep the room safe, use the backup location you identified. CDC guidance points people to 2-1-1 and local health or emergency-management agencies for information about available air-conditioned sites. Bring medication, water, phones, backup batteries, and required medical-device power supplies. Keep refrigerator and freezer doors closed as much as possible during an outage, and follow local advice for medicines that require refrigeration.
Cool the body while you cool the home
Room temperature control reduces exposure, but people also need direct cooling and adequate fluids.
- Drink water regularly. Limit alcohol and excessive caffeine, which can complicate hydration.
- Take a cool shower or bath, or wet the skin with a damp cloth or spray.
- Wear light, loose clothing and use light bedding.
- Use urine color only as a rough hydration cue. Medical conditions and medicines can change fluid requirements, so follow a clinician’s personalized advice rather than forcing a standard amount.
Combine these measures with a cooler room or air-conditioned location; body-cooling steps are not a reason to remain in a dangerously hot building. Offer fluids and help with cooling to anyone who cannot safely manage these tasks alone.
Give higher-risk people earlier help
Heat can worsen existing conditions. Arrange scheduled check-ins rather than assuming someone will call for help. Ask whether the person is drinking, whether their room is below the relevant target, and whether they have access to air conditioning or a transport plan. A missed call, unusual sleepiness or a change in behavior should prompt an in-person check when it is safe to do so.
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- Adults over 65 and infants can become dangerously hot quickly.
- Heart, lung, kidney, and other chronic diseases can make heat harder to tolerate.
- People with disabilities may need help operating equipment, traveling, drinking, or recognizing symptoms.
- Anyone living alone needs a named person responsible for contact, including during an outage.
- Pets need water and a cooler space; include them when relocating.
Recognize heatstroke and act immediately
Confusion, delirium, fainting, loss of consciousness, severe dizziness, or nausea that is worsening are emergency warning signs. Call emergency services immediately. While help is coming, move the person to a cooler place and cool the skin with water or wet cloths. Do not delay emergency care while trying additional home remedies. Do not leave a confused or faint person alone, and tell responders the person’s symptoms and the indoor conditions.
When to leave for a cooling center or other public place
Go before conditions become an emergency when the home cannot stay near the WHO targets, when cooling equipment or power fails, or when a vulnerable person cannot rest safely. A few hours in an air-conditioned library, mall, cooling center, public building, or trusted friend’s home can reduce heat exposure. Confirm local availability by calling 2-1-1 or contacting local health or emergency-management agencies, because locations and hours vary by geography and date.
A practical relocation checklist
- Bring water, medicines, identification, phones, chargers, and backup batteries.
- Pack essential medical-device power supplies and any items needed for disability support.
- Take pet supplies if the destination allows animals, or arrange separate pet care.
- Tell a relative or neighbor where you are going and when you expect to return.
- Continue monitoring symptoms even after reaching a cooler building.
Quick heatwave decision guide
| Situation | Action |
|---|---|
| Outside hotter than indoors | Close windows, shade sunny glass, switch off unnecessary equipment, and use the coolest room. |
| Outside cooler after dark | Open windows if safe, then close them before outside warms above indoors. |
| Indoor temperature reaches 90°F (32.2°C) or more | Do not rely on a fan alone; arrange air conditioning or leave for a cool public place. |
| Indoor temperature remains above WHO targets | Escalate earlier, especially for vulnerable people or anyone sleeping in the room. |
| Confusion, fainting, delirium, loss of consciousness, severe dizziness, or worsening nausea | Call emergency services, move the person to a cooler place, and wet the skin while waiting. |
Frequently Asked Questions
How do I keep my house cool during a heatwave?
Close windows and exterior doors when outside air is hotter, shade sun-facing glass, turn off unnecessary lights and electronics, limit stove and oven use, and move to the coolest room. Open windows after dark only when outdoor air is cooler than indoor air, then close them before morning heating.
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Is it safe to use a fan when it is over 90 degrees?
CDC guidance says to use indoor fans only when temperatures are below 90°F (32.2°C), because above that a fan can increase body temperature. WHO also warns that above 35°C (95°F) an electric fan may not prevent heat illness. Move to air conditioning or a cool public place instead of relying on a fan.
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- Face Icon Comfort Indicator: Humidity temperature gauge features face icons to indicate DRY/COMFORT/WET air conditions, quickly informs you how to adjust your humidifier or dehumidifier to achieve optimal comfort
- Highly Accurate Sensors: This temperature humidity sensor features a high accuracy of +/-1°F/°C and +/-2% to 3%RH, making it ideal for measuring dynamic environments like greenhouses
- Fast Refresh Rate: This digital indoor thermometer refreshes every 10 seconds to provide the latest updates for temperature and humidity readings
- Compact Display with Large Digits: This digital thermometer indoor outdoor features a compact LCD display with large bold digits, allowing you to read the room thermometer indoor from any angle and distance
- Multiple Placement Options: This humidistat has 3 placement options - Tabletop Stand / Magnetic Back / Hanging Mount, place the wall thermometer anywhere you wish such as living room, baby room, kitchen, greenhouse, guitar room, office or cellar
What temperature is too hot inside the house?
WHO advises aiming for below 32°C (89.6°F) during the day and below 24°C (75.2°F) at night. These are protective targets, not a universal medical cutoff. If your home remains above them, escalate sooner, especially for vulnerable people.
How can I cool my home without air conditioning?
Use blackout or thermal shades, keep windows closed while outside air is hotter, reduce heat from lights and appliances, use the coolest room, and ventilate after dark when outside is cooler. Do not rely only on electric fans during extreme heat; relocate to an air-conditioned place if the home stays dangerously hot.
When should I go to a cooling center?
Go when your home cannot remain near the WHO targets, power or cooling equipment fails, or a vulnerable person cannot sleep or rest safely. Contact 2-1-1 or local health or emergency-management agencies for current locations and hours.
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Call emergency services immediately. Move the person to a cooler place and cool the skin with water or wet cloths while help is coming. Do not delay emergency care to continue home remedies.
What air-conditioner setting is recommended?
WHO guidance cited here recommends 27°C (81°F) and says adding an electric fan can make the room feel about 4°C cooler. Keep doors and windows closed while the air conditioner operates and follow the manufacturer’s electrical and installation instructions.
Who needs extra checking during a heatwave?
Check adults over 65, infants, people with heart, lung, kidney or other chronic conditions, people with disabilities, and anyone living alone. Check pets too, and follow a clinician’s advice about fluids or cooling when medical conditions or medicines affect those needs.
The Bottom Line
Keep heat and sunlight out during the day, ventilate only when outdoor air is cooler, and check indoor temperature at 08:00–10:00, 13:00 and after 22:00. Use fans only below 90°F (32.2°C), and do not rely on them above that or above 35°C (95°F). Move to air conditioning or a verified cool public place before conditions become an emergency, and call for help immediately if heatstroke signs appear.
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