Part VI: Staying CoolChapter 10. Passive and Low-Energy Cooling
Living Comfortably Without Air Conditioning
Habits, air movement, and humidity that make a warm house tolerable when you skip mechanical cooling.
- Difficulty
- Beginner
- Cost
- Free
A house without air conditioning can be comfortable in a mild summer if you keep the sun out, move air across people, and let the cool part of the night in. It can be dangerous in a heat wave, especially for older people, very young children, and anyone whose body does not shed heat well. This page is the first kind of weather. If the indoors is dangerously hot, the plan is mechanical cooling, a cooler building, or leaving. Habits are not a treatment.
The building half is already written. Shade the glass from outside. Flush with night air when that air is cooler and not soggy. A lighter roof helps a thin attic and does little for a west window. This page is what the people do during the day those projects are working.
Difficulty
- Level
- Beginner
- Time
- A change of habits for the season
- Skills
- Noticing whether the outdoors is a resource or a threat
Cost estimate
Free
Fans you already own, shades you already have, and a thermometer. A dehumidifier in a sticky climate is a real appliance and not free. Neither is a safe place to go when the house is too hot.
Materials
| Item | Qty | Notes |
|---|---|---|
| A thermometer | 1 | Indoors, in the room you actually occupy. The number matters more than the feeling at the start of a heat wave. |
| Exterior shade or shades you can close | On the sunny glass | Outside the glass if you can. Inside the glass is the leftover. |
| A fan that blows on people | 1 or more | Ceiling or a room fan. It cools people by helping sweat evaporate. It does not cool the room much. |
| A cooler place you can reach | Named in advance | Another building, a cooling center, or a household that has air conditioning. Decide before the worst day. |
When to close up and when to open
When the outdoor air is hotter than the indoor air, the windows stay shut and the sun stays outside. Close the east shades in the morning and the west shades before the sun arrives there. Do not bake a room "for the light" and then hope a fan undoes it. Cooking, drying clothes, and a dishwasher's heated dry are indoor heaters. Move them to the cool part of the day or out of the house.
When the outdoor air is cooler, open up. Cross ventilation needs an inlet and an outlet, not one cracked window in a shut room. A whole-house fan is the powered version, with the combustion cautions on that page. In the morning, close again before the day climbs in, or the warm air undoes the night's cooling.
Air moving across skin helps while sweat can evaporate. Dry air and a fan can make 80 degrees F feel workable. The same fan in very hot, very humid air may not be enough, and public-health guidance treats fans as inadequate once the air itself is dangerously hot. Believe that over a gadget. A dehumidifier helps in a sticky climate and adds some heat of its own.
Who this fails
People who are old, very young, ill, or on medicines that affect heat tolerance do not have the same margin. A stuffy bedroom at the top of the house is the usual bad room. Sleep on a lower floor if that floor is cooler. Check on anyone who might not notice they are in trouble. Thirst, a pounding head, confusion, and skin that is hot and dry or that has stopped sweating are reasons to get medical help, not reasons to try a different fan setting.
Never use a grill, a camp stove, or a generator indoors or in a closed garage to "just get through" a hot night. The added heat is bad, and the carbon monoxide is worse. A generator stays outdoors, away from windows and the sunspace, and on a circuit that cannot backfeed the house.
Pets and anyone who cannot open a window themselves are part of the plan. A closed car and a closed sunroom heat faster than the house. Do not leave a living thing in either one.
Keep the sun out of the glass
Exterior shade first. Interior shades if that is all you have. West glass is the afternoon problem.
Close up while the outdoors is hotter
Windows shut, indoor heat sources delayed, fans on people rather than in a closed hot attic.
Open up only when the night is cooler
Cross breeze or a fan with enough inlet. Skip muggy nights that will wet the walls. Close again in the morning.
Name the backup place before you need it
If the indoor temperature is dangerous, go there. Do not wait to see if the next habit helps.
Further reading
These links go to outside sources. This book cites them by link and does not copy their words or pictures.
- https://www.builditsolar.com/Projects/Cooling/passive_cooling.htm
- https://www.builditsolar.com/Projects/Cooling/Shading/Shading.htm
- https://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm
- https://www.builditsolar.com/Projects/Cooling/NoAC/ComfortWithNoAC.htm
- https://www.builditsolar.com/Experimental/RoofCooling.htm
- https://www.builditsolar.com/Experimental/RadiationCool/EvaproRad.htm
- https://www.builditsolar.com/Experimental/VentSize/
General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.