Keeping cool indoors when it is hot outdoors is a problem. The sun beating down on the homes causes indoor temperatures to rise to uncomfortable levels. Air conditioning provides some relief. But the initial costs of installing an air conditioner and the electricity costs to run it can be high. In addition, conventional air conditioners use refrigerants made of chlorine compounds, suspected contributors to the depletion of the ozone layer and global warming. But there are alternatives to air conditioning.
An alternative way to maintain a cool house or reduce air-conditioning use is natural (or passive) cooling. Passive cooling uses non-mechanical methods to maintain a comfortable indoor temperature.
Specific methods to prevent heat gain include:
Dull, dark-colored home exteriors absorb 70 to 90 percent of the radiant energy from the sun that strikes the home's surfaces. Some of this absorbed energy is then transferred into a home by way of conduction, resulting in heat gain. In contrast, light-colored surfaces effectively reflect most of the heat away from a home.
Instructions: Place your cursor over the numbers of the image below to learn more about reflecting heat away.
Click here to open a text description of the Reflecting Heat Away activity.
The following are passive methods for reflecting unwanted heat energy away from your home.
1) The roof, made out of traditional roofing materials, allows about 1/3 of unwanted heat that builds up in the home. Unlike most light-colored surfaces, even white asphalt and fiberglass absorb 70 percent of the solar radiation. One solution is to apply a reflective coating to your existing roof. Two standard roofing coatings are marketed primarily for mobile homes and recreational vehicles. Both are waterproof and have reflective properties.
2) Wall color is not as important as roof color, but it does affect heat gain somewhat. White exterior walls absorb less heat than dark walls. And light, bright walls increase the longevity of siding, particularly on the east, west, and south sides of the house.
3) Windows permit about 40 percent of the unwanted heat that builds up in the home. Reflective window coatings are plastic sheets treated with dyes or thin layers of metal. Besides keeping your house cooler, these reflective coatings cut glare and reduce fading of furniture, draperies, and carpeting. Two main types of coatings include sun-control films and combination films.
Two excellent methods to block heat are insulation and shading.
Insulation helps keep your home comfortable and saves money on mechanical cooling systems such as air conditioners and electric fans.
Instructions: Place your cursor over the numbers of the image below to learn more about using insulation and shading to block heat.
Click here to open a text description of the Blocking the Heat activity.
The following are passive methods for blocking unwanted heat energy from your home.
Nothing feels better on a hot day than a cool breeze. Encouraging cool air to enter your house forces warm air out, keeping your house comfortably cool. However, this strategy only works when the inside temperature is higher than the outside temperature.
Natural ventilation maintains indoor temperatures close to outdoor temperatures and helps remove heat from your home. But only ventilate during the coolest parts of the day or night, and seal off your house from the hot sun and air during the hottest parts of the day.
The climate you live in determines the best ventilation strategy.
Climate | Strategy |
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Cool nights and very hot days | Let night air cool the house. A well-insulated house will gain only 1° F (0.6° C) per hour if the outside temperature is 85° to 90° F (29° to 32° C). By the time the interior heats up, the outside air should be cooler and can be allowed indoors. |
Daytime breezes | Open windows on the side from where the breeze is coming and on the opposite side of the house. Keep interior doors open to encourage whole-house ventilation. If your location lacks consistent breezes, create them by opening windows at the lowest and highest points in your house. This natural "thermosiphoning," or "chimney," effect can be taken a step further by adding a clerestory or a vented skylight. |
Hot and humid where temperature swings between day and night are small | Ventilate when humidity is not excessive. Ventilating your attic greatly reduces the amount of accumulated heat, which eventually works its way into the main part of your house. Ventilated attics are about 30° F (16° C) cooler than unventilated attics. Properly sized and placed louvers and roof vents help prevent moisture buildup and overheating in your attic. |
Often-overlooked sources of interior heat gain are lights and household appliances, such as ovens, dishwashers, and dryers.
Heat generating light or appliance | Reducing Heat |
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Incandescent Lamps | Use only when necessary and take advantage of daylight to illuminate house. Also consider switching to fluorescent lamps, which use 75% less energy than incandescent lamps and emit 90% less heat for the same amount of light. |
Kitchen Appliances | Use in the morning or late evening when extra heat can be tolerated. Consider cooking on an outside grill or using the microwave oven, which does not generate as much heat and uses less energy than a gas or electric range. |
Laundry Appliances | Seal off laundry room and water heater from rest of room. Purchase new energy-efficient appliances that generate less heat and use less energy. Look for the Energy Guide label indicating the annual estimated cost for operating the appliance or a standardized efficiency ratio, and use this information to select the most efficient model for your needs. |
See Resources document for more information on energy-efficient lighting and appliances.