How to Cool a Room Without AC: What Actually Works

The short answer

To cool a room without AC, stop the heat from getting in, then move it out. Close shades or blinds on sunny windows during the day, open windows and run a window fan at night once the outdoor air turns cooler, and skip the oven. Point a fan at yourself for comfort, take cool showers, and once the room passes about 90°F (32°C), stop aiming the fan at yourself and head somewhere air-conditioned (DOE Window Coverings; DOE Natural Ventilation; EPA Heat Guidebook).

Block the sun first

Sunny windows heat a room fast. In summer, about 76% of the sunlight that lands on standard double-pane windows enters the room and turns into heat (DOE Window Coverings). Block it at the glass and you have less heat to clear out later.

What the Department of Energy reports for common window coverings (DOE Window Coverings):

• Cellular shades, fitted tightly, can cut unwanted solar heat through a window by up to 60%.
• Medium-colored drapes with white plastic backings cut heat gain by about 33% in studies.
• Exterior awnings reduce solar heat gain by up to 65% on south-facing windows and 77% on west-facing ones.
• Highly reflective blinds, fully closed and lowered on a sunny window, reduce heat gain.
• Window films block solar heat and glare. Silver, mirror-like films tend to outperform colored, more transparent ones, and east- and west-facing windows benefit most. Check first: most window makers void the warranty if you apply film to an insulated glass unit.

Moving the blinds you already own costs zero dollars. Yet the same DOE page notes that 75% of home window coverings stay in the same position every day. Blinds work best when you actually move them. Close them before the sun hits that side of the house, and open them after it moves on.

How fans make a room feel cooler

Fans move air without chilling it. They cool you by moving air across your skin and creating a wind chill effect, so the DOE suggests turning them off when you leave a room (DOE Fans). For how wind and humidity change what your body feels, see our guide to the feels like temperature.

That breeze buys you real comfort:

• In homes with AC, a ceiling fan lets you raise the thermostat about 4°F (about 2°C) with no loss of comfort, and in moderately hot weather a fan may let you skip the AC altogether (DOE Fans).
• In a field study from UC Berkeley's Center for the Built Environment, office workers given ceiling fans felt equally or more comfortable at 79 to 81°F (26 to 27°C) than they had at 73°F (23°C) without fans. Lab studies found air movement kept people comfortable as high as 86°F (30°C) at 80% relative humidity (CBE Ceiling Fans).
• More than 35,000 occupant surveys in the ASHRAE Global Thermal Comfort Database show that people want more air movement than buildings usually give them (CBE Ceiling Fans).

A ceiling fan works best with its blades 7 to 9 feet above the floor, in a room with a ceiling at least 8 feet high (DOE Fans).

When a fan stops helping

Fans hit a limit in real heat. Once the air runs warmer than your body, a fan blows that hot air across your skin. The EPA heat guidebook, written with the CDC, says a fan alone increases heat stress once the heat index climbs past 99°F (37°C), and it advises against aiming a portable fan at yourself when the room tops 90°F (32°C). The extra airflow can also speed the onset of heat exhaustion (EPA Heat Guidebook).

The CDC puts it plainly: electric fans might feel good, but when temperatures get really hot, they won't prevent heat-related illness (CDC No AC).

Cross-ventilation and night flushing

Moving air through the house can lower the room temperature itself, as long as the incoming air runs cooler than the air inside.

• Cross-ventilation. Wind pushes air in through windows on the side facing it and pulls air out through windows on the downwind side. Hot air also rises, so cool air can come in low and leave through upper windows (DOE Natural Ventilation).
• Window fans. Place a box fan in or beside an open window so it exhausts hot air outside or draws cooler air in (EPA Heat Guidebook). The DOE suggests aiming window fans away from the prevailing wind, and using several together to pull air through the house (DOE Fans).
• Night flushing. Keep the house shut during the day and ventilate at night. This works best in dry climates with cool nights (DOE Natural Ventilation).

In humid climates, outdoor air brings moisture with it, and the DOE warns that natural ventilation there can contribute to mold and mildew. It also doesn't filter the air (DOE Natural Ventilation).

Cut the heat you make indoors

Every appliance that runs hot warms the room around it. The CDC suggests using your stove and oven less to keep your home cooler (CDC No AC). On the hottest days, lean on meals that need little or no cooking. The EPA's tip list happens to agree, recommending light, cool, easy-to-digest foods such as fruit or salads (EPA Heat Guidebook).

Lower the humidity

Fans cool you by helping sweat evaporate (EPA Heat Guidebook), and damp air can make that harder. Our guide to ideal indoor humidity covers the range to aim for and how to get there. If you live somewhere muggy, favor sealed-up daytime shading and fans over open windows, for the mold reasons above.

Cool your body directly

When the room won't cooperate, cool yourself:

• Take cool showers or baths (CDC No AC).
• Put cool, wet cloths on your skin (EPA Heat Guidebook).
• Wear loose, light-colored clothes (EPA Heat Guidebook).
• Drink more water than usual, before you feel thirsty (CDC No AC).
• Spend a few hours somewhere air-conditioned, like a mall or library (CDC No AC).

For bedrooms, the same steps apply, and our guide to the best temperature for sleep explains what range to aim for. You can also read more about why the perfect temperature changes with weather, body and time of day.

Which methods help most

| Method | What the sources report | Cost | |---|---|---| | Close shades and blinds | Tight cellular shades cut solar heat through a window up to 60% | Free if you own them | | Exterior awnings | Up to 65% less solar heat (south), 77% (west) | Purchase and install | | Ceiling fan | Feels comfortable about 4°F (2°C) warmer | Purchase | | Portable fan aimed at you | Comfort only; skip it above 90°F (32°C) | Low | | Window fan at night | Pulls in cooler air; best in dry climates | Uses little energy | | Skip the oven | Less indoor heat | Free | | Cool shower, wet cloth | Cools your body directly | Free |

(Sources: DOE Window Coverings; DOE Fans; DOE Natural Ventilation; EPA Heat Guidebook; CDC No AC.)

When a hot room gets dangerous

A hot room can make anyone sick, and the EPA guidebook asks you to check on older, sick or frail people who may need help (EPA Heat Guidebook). The CDC says to seek medical care right away for symptoms of heat-related illness such as muscle cramps, headache, nausea or vomiting (CDC No AC). Our guide to heat stress symptoms walks through heat exhaustion versus heat stroke.

Call 911 for anyone who seems confused, passes out, or has a very high body temperature. The EPA guidebook calls heat stroke a severe medical emergency. While help comes, move the person somewhere cooler, cool them with a mister, fan or sponging, and don't give them fluids (EPA Heat Guidebook).

Use the buddy system during a heat wave: check on a neighbor and have someone check on you (CDC No AC).

The bottom line

Shade the windows by day, move cooler air through at night, and use fans to cool yourself while the room stays under about 90°F (32°C). Cut indoor heat, cool your body with water, and leave for an air-conditioned space when the heat climbs past what a fan can handle. This guide shares general information and can't replace care from your own clinician.