Heat kills more Americans every year than hurricanes, tornadoes, and floods combined. It kills quietly — no dramatic footage, no breaking news coverage — just people found dead in their homes after a multi-day heat event with no power. The 1995 Chicago heat wave killed 739 people in five days. The majority were elderly, living alone, in apartments with no air conditioning, afraid to open windows. They died of something entirely survivable with the right knowledge.
A grid-down scenario in summer is not a minor inconvenience. In a humid continental climate like central Illinois, where heat index values regularly exceed 105°F in July and August, losing air conditioning during a heat event can become life-threatening within 24-48 hours for vulnerable individuals. This post covers how to keep a building cool, how to keep people cool, and how to recognize when someone is past the point where field management is enough. See Heat Stroke for the medical protocol.
UNDERSTAND WHAT YOU ARE FIGHTING
Cooling without electricity is not about making things comfortable. It is about keeping core body temperature below the threshold where physiology starts failing. That threshold is approximately 104°F — above that, you are in heat stroke territory. Everything in this post is in service of staying below that line.
Two factors determine how hard that is: air temperature and humidity. High humidity prevents evaporative cooling — sweat cannot evaporate efficiently when the air is already saturated with moisture. This is why a 95°F day at 80% humidity in Illinois is more dangerous than a 105°F day at 10% humidity in the desert. The heat index — the “feels like” temperature that combines heat and humidity — is the number that matters. Track it.
The human body generates heat through metabolism and activity. Every calorie burned produces heat. In a heat event: reduce physical activity, avoid direct sun, eat lighter meals (digestion generates heat), and prioritize the cooling strategies below.
THE BUILDING — PASSIVE COOLING
The goal is to keep the building cooler than the outside air by managing solar heat gain, ventilation, and thermal mass. A well-managed house can stay 10-20°F cooler than outside air during the day using passive strategies alone.
Block solar heat gain during the day. The sun heating your roof and walls is the primary source of indoor heat gain. Close all blinds, curtains, and window coverings on the sunny side of the house before the sun hits them — not after the room is already hot. Reflective window coverings (emergency mylar blankets taped inside windows, reflective window film, or even aluminum foil) reflect solar radiation back out significantly better than standard curtains. The south and west-facing windows drive the most heat in afternoon — prioritize those.
Open up at night. Once outside air temperature drops below indoor temperature — typically after 10pm-midnight in a heat event — open everything. Cross-ventilate: open windows on opposite sides of the house to create airflow. Use fans (battery-powered or hand fans) to accelerate the exchange. The goal is to flush stored heat out of the building’s thermal mass and bring in cooler night air. Close everything again before the sun rises and the temperature starts climbing.
The lowest point in the building is the coolest. Heat rises. Basements stay significantly cooler than upper floors — often 15-20°F cooler during heat events. If you have a basement, this is where people sleep and spend time during the hottest part of the day. Ground floor is cooler than second floor. Consolidate people into the coolest available space and stop heating the spaces you are not using.
Reduce internal heat sources. Cooking generates substantial heat — avoid using the oven or stove during the hottest hours. Cook outside, cook at night, or eat food that requires no cooking. Every light bulb (particularly incandescent), every running appliance, every electronic device generates heat. In a grid-down scenario, most of these are already off. Keep it that way.
Thermal mass works both ways. Concrete floors, stone, tile, and brick absorb heat during the day and release it at night — in winter this is a feature, in summer it is a liability if not managed. Covering thermal mass surfaces with rugs and keeping them shaded reduces daytime heat absorption. In a building without significant thermal mass (standard wood-frame construction), temperatures track outdoor air more quickly, which means the night-opening strategy works faster.
EVAPORATIVE COOLING — WHERE IT WORKS AND WHERE IT DOESN’T
Evaporative cooling works by using the heat energy in air to evaporate water, which removes that heat from the surrounding environment. This is how sweating works. It is the basis of swamp coolers. It requires low humidity to function — evaporation cannot happen in already-saturated air.
In low-humidity conditions (below 50% relative humidity): Evaporative cooling is highly effective. Hang wet sheets in front of open windows. Mist yourself with water and sit in airflow. A battery-powered fan blowing across a wet surface significantly lowers the perceived temperature.
In high-humidity conditions (above 70% relative humidity — Illinois in July): Evaporative cooling is significantly less effective. The air cannot absorb much more moisture. Focus shifts to conduction and convection cooling instead.
Conduction cooling: Direct contact with cool surfaces. Damp cool cloths applied to pulse points — wrists, neck, armpits, groin, temples. These are locations where blood vessels run close to the skin surface; cooling the blood there cools the entire circulation. A cool damp cloth on the back of the neck is one of the most effective immediate cooling interventions available without electricity. Change and re-cool the cloth as it warms.
Wet towel technique: Soak a lightweight towel or sheet in cool water, wring it partially out, and drape over the body. The residual evaporation provides cooling and the cool wet fabric conducts heat away from the skin directly. Re-wet as it dries or warms.
WATER — INTERNAL COOLING
The body’s primary cooling mechanism is sweating. Sweating requires water. In a heat event with significant activity or even minimal exertion, an adult can lose 1-2 liters of sweat per hour. Dehydration impairs sweating efficiency, which impairs cooling, which accelerates heat illness.
Drink before you are thirsty. Thirst is a lagging indicator — by the time you feel thirsty in heat, you are already meaningfully dehydrated. In a heat event, adults should be drinking 1 liter of water per hour during active periods and maintaining continuous hydration throughout the day.
Plain water is adequate for moderate activity. For heavy sweating over extended periods, electrolyte replacement is necessary — sodium, potassium, and magnesium lost in sweat need replacement. See the ORS discussion in Shock — Recognition & Response. Salt food aggressively during heat events. A pinch of salt and a small amount of sugar or honey in water is a functional oral rehydration solution when commercial ORS is unavailable.
Do not rely on alcohol, caffeine, or sugary sodas for hydration during heat events. All are diuretic or metabolically taxing in ways that worsen heat tolerance.
Cool water internally: Drinking cool water lowers core temperature directly. If water is available at cooler temperatures — from a basement, a well, a cooler with ice — drink it rather than room-temperature water. The internal cooling effect is modest but real and cumulative.
PEOPLE — PRIORITY MANAGEMENT
Not everyone in a household faces the same heat risk. Identify who needs the most active management.
Highest risk: Infants and young children (cannot self-regulate or self-report), elderly individuals (reduced sweating capacity and thirst sensation, often on medications that impair heat tolerance), anyone on medications (diuretics, anticholinergics, beta-blockers, antipsychotics — see the medications list in Know Your Medication), anyone who is ill, immunocompromised, or has cardiovascular or kidney disease.
Keep high-risk individuals in the coolest available space. This is not a suggestion. In a serious heat event, an elderly person on the second floor of a house at 95°F indoor temperature is at genuine risk. Move them to the basement or coolest ground-floor room.
Check on them frequently. Heat illness impairs the ability to recognize heat illness. Someone who is becoming confused or lethargic in heat may not be able to tell you they are in trouble. Check on vulnerable individuals every 30-60 minutes during serious heat events.
Babies and young children cannot tell you they are hot and their thermoregulation is immature. Signs of heat stress in infants: flushed or very pale skin, irritability beyond normal, reduced wet diapers (dehydration), lethargy, rapid breathing. Keep infants in the coolest available space and maintain skin contact — your body temperature, while warmer than cool air, is regulated and stable, and skin-to-skin provides comfort and monitoring.
IMPROVISED COOLING TOOLS
Battery-powered fans — The most important single piece of cooling equipment for grid-down summer scenarios. Stock multiple sizes. A box fan running on a deep cycle battery with an inverter is the highest-output option. Small USB fans running from battery banks are useful for personal cooling. The fan itself does not lower air temperature — it increases evaporative and convective cooling from the skin. In humid conditions this effect is reduced but still meaningful.
Ice and cool water — If you have ice or access to cool water (well water is typically 50-55°F year-round), use it for cooling cloths, foot soaks, and drinking. A foot soak in cool water provides significant systemic cooling — the feet have high surface area relative to blood flow and cool quickly. A basin of cool water for the feet during the hottest hours costs almost nothing and provides real relief.
Cooling towels — Commercial evaporative cooling towels (available at sporting goods stores, $5-15) stay significantly cooler than ambient temperature when wet and in airflow. Stock several. They are reusable, pack small, and work in lower-humidity conditions.
Shade structures — Outdoor shade dramatically reduces radiant heat. A tarp, shade cloth, or awning over windows, doors, or outdoor work/rest areas reduces surface temperatures significantly. The temperature under shade on a 95°F day can be 15-20°F lower than in direct sun.
Underground spaces — If you have a root cellar, storm shelter, or crawl space that is earth-contacted, the ground temperature at 4-6 feet below grade is approximately 55°F year-round regardless of surface temperature. This is free cooling that requires no power or equipment. Spending the hottest hours in or near an earth-contacted space is the most effective passive cooling available.
RECOGNIZING WHEN IT IS NOT ENOUGH
Passive and evaporative cooling can maintain survivable conditions in most heat events for healthy adults. They may not be sufficient for vulnerable individuals in extreme heat events. Know when field management is failing:
- Indoor temperature sustained above 90°F with no prospect of night cooling
- Vulnerable individual showing confusion, lethargy, or stopping sweating despite heat
- Core temperature (if measurable) above 101°F and not responding to cooling measures
- Anyone who has stopped drinking fluids or is vomiting
When field management is not enough, the options are: access to a vehicle with air conditioning (a car running its AC is an effective cooling resource even without electricity in a building), access to a public cooling center (libraries, community centers, churches — these are activated during heat emergencies), or evacuation to a location with reliable cooling.
See Heat Stroke for the full medical protocol when someone has crossed into heat illness.
WHAT TO STOCK
- Battery-powered box fan + deep cycle battery + inverter ($100-200 total)
- Multiple small USB fans + large battery banks
- Cooling towels (6-10)
- Emergency mylar blankets (for window reflection — doubles as cold weather gear)
- Shade cloth or tarps for exterior shade
- ORS packets (oral rehydration — critical in heat)
- Spray/mist bottles (2-3, large capacity)
- A reliable thermometer — both indoor and a medical thermometer for monitoring people
Cross-reference: Heat Stroke | Shock — Recognition & Response | Hypothermia | Grid Down — First 72 Hours | Water — Finding, Filtering, Storing