Heat accumulates in homes from several sources and can make indoor temperatures higher than outdoors even in the hottest weather. Solar energy – which enters a home primarily through the roof and windows – is a major source of unwanted heat in most climates. Appliances, lights, and occupants generate heat as well.

To use ventilation instead of air conditioning for cooling, you should prevent heat from entering and accumulating in your home as much as possible. Some preventive measures include installing additional attic insulation, awnings, and sun-blocking window treatments. Operational changes – such as reducing the use of appliances, lighting, and hot water – will also reduce accumulated heat.

Natural Ventilation relies on the wind and the “chimney effect” to keep a home cool. The wind will naturally ventilate your home by entering or leaving windows, depending on their orientation to the wind. When wind blows against your home, air is forced into your windows. Heat accumulates in your home during the day, and the cool night air can flush it out.

The chimney effect occurs when cool air enters a home on the first floor or basement, absorbs heat in the room, rises, and exits through upstairs windows. This creates a partial vacuum, which pulls more air in through lower-level windows.

You can create natural cross-ventilation by opening your windows and doors, and adjusting the size and location of the openings to ventilate different parts of the house. Inlets and outlets located directly opposite each other cool only those areas in between, in the direct path of the airflow. You’ll cool more of your home if you force the air to take a longer path between the inlet and outlet. Air from cooler, shaded outdoor areas provides the best intake air. Experiment with different patterns of window venting to move fresh air through the living areas of your home.

Solar heat travels in through the roof and radiates into the attic. Attic ventilation reduces attic temperature 5-15^oC (10 to 25^oF) and slows the transfer of heat into the living space.*

Circulating Fans include ceiling fans, table fans, window fans and fans mounted to poles or walls. They create a wind chill effect that will make you more comfortable in your home, even if it’s also cooled by natural ventilation or air conditioning.

If you’re using air conditioning, a ceiling fan will allow you to raise the thermostat setting about 2^oC (4^oF) with no reduction in comfort – sometimes they may allow you to avoid using your air conditioner altogether. Install a fan in each room that needs to be cooled during hot weather. Fans work best when the blades are 2.2-2.7 m (7–9’) above the floor and 25–30 cm (10–12”) below the ceiling. Larger ceiling fans can move more air than smaller fans. A larger blade will also provide comparable cooling at a lower velocity than a smaller blade. This may be important in areas where loose papers of other objects will be disturbed by a strong breeze.

• When shopping for circulating fans, be sure to test the fan for noise. Listen to the qualities of each fan’s sound. Fans also will be marked with their rated noise level, measured in “sones”. Very quiet fans are rated at 1.5 sones.
• Poor installation can affect a fan’s noise level. If a fan isn’t installed securely, it can vibrate and rattle, making as much noise as a poorer-quality fan.

Excerpt from the U.S. Department of Energy - National Renewable Energy Laboratory publication DOE/GO-102001-1278- FS228

*Adequate ventilation requires a combination of vents located as high and as low on the roof as possible. This type of attic ventilation system includes ridge, roof, soffit and gable vents. For maximum airflow, the area of high roof vents should equal or exceed the low vent area. How much ventilation is enough? For very 279m² (3000ft²) of attic floor, you should have 0.9m² (10ft²) of unobstructed ventilation. Vents are measured in “Net Free Area” (NFA), the amount of free space, minus baffles and screens, which should be stamped or affixed to each vent. Vents should be located to give good cross ventilation from end to end and top to bottom. Ensure that eave vents are not blocked by insulation.