Why cooling is harder than heating
In winter you can burn something. Propane, wood and natural gas all make heat directly, which is why staying warm without power has good answers that do not involve electricity at all.
There is no equivalent for cold. Refrigeration requires a compressor, a compressor requires a motor, and a motor requires electricity. Every route to a cooler room runs through watts.
So the strategy has to change: stop trying to cool the room, and start trying to cool the person.
The numbers that force the decision
| Approach | Draw | Hours from 1,056 Wh |
|---|
| USB or battery personal fan | 5-15 W | Days |
|---|
| Box or pedestal fan | About 50 W | About 18 hours |
|---|
| Ceiling fan | 15-90 W | 10 hours to days, but usually hardwired |
|---|
| Evaporative cooler, small | 50-200 W | 4-18 hours, and only useful in dry climates |
|---|
| Window air conditioner | 1,200 W running, more to start | About 45 minutes |
|---|
| Central air conditioning | 3,000-5,000 W to start | Will not start at all |
|---|
Hours are 1,056 Wh x 0.85 / draw. Fan and air conditioner figures are the ranges used across this site; see the appliance wattage chart.
The gap between rows two and five is a factor of twenty-four. That is the entire argument for fans, and it is why a modest battery plus a fan outperforms a large battery plus an air conditioner for every hour after the first.
Why a fan works when it makes no cold
A fan does not lower air temperature — it slightly raises it, because the motor produces heat. What it does is move air across skin, which speeds evaporation of sweat and carries heat away from the body.
The practical effect is a perceived temperature drop of several degrees for a load of fifty watts. That is the best efficiency available anywhere in this problem.
Two consequences worth acting on. A fan pointed at a person does far more than a fan pointed at a room, so aim it. And a fan in an empty room is pure waste, so turn it off when you leave.
The free moves, in order
1. Close the house during the day. Windows, blinds and curtains shut on the sunny side. Most summer heat gain is solar through glass, and blocking it costs nothing.
2. Open it at night. Once outside is cooler than inside, open windows on opposite sides and put a fan in one of them pointing out. A whole house can be flushed in an hour this way.
3. Move downstairs. Heat stratifies. A basement can be ten degrees cooler than an upstairs bedroom without anything being done to it.
4. Stop making heat. No oven, no stove, no dryer. Cook outdoors on a propane stove instead — the cooking page covers that.
5. Cool the person. Damp towel on the neck, cool shower, feet in cold water, loose clothing. These are genuinely effective and cost nothing.
The part that is actually dangerous
Heat kills more people in the United States in a typical year than any other weather hazard, and a summer outage removes cooling from exactly the households least able to manage without it.
- Know the warning signs. Heavy sweating that stops, confusion, a rapid pulse and a very high body temperature are heat stroke and are a medical emergency, not something to manage at home.
- Check on older neighbors. Older adults lose heat less efficiently and are less likely to feel thirsty.
- A fan alone stops helping above about 95 degF. Past that, moving hot air over skin does little, and the right move is to go somewhere air conditioned — a cooling center, a library, a relative.
- Drink water before you feel thirsty, and remember a well pump will not be running. The water storage page covers what to keep.
The refrigerator is the other summer problem
Summer outages are the ones where food spoils fastest, and the ambient temperature makes a closed refrigerator lose its four-hour margin more quickly than in winter.
If you have to choose what the battery runs, the refrigerator beats the fan — the freezer page covers the food-safety timings. A fan on a separate battery solves both.
The short version
- Cool the person, not the house. 50W versus 1,200W.
- Close up by day, flush the house at night. Free, and the biggest single effect.
- A window unit is about 45 minutes on a 1,000Wh battery. Plan for bursts, not sessions.
- Above about 95 degF a fan stops being enough. Go somewhere cooled.
