Whole house fans pull in cooler air from outside and exhaust the stale house air in to the attic space. Whole house fans can reduce or eliminate the need for air conditioning. Whole house fans are different from attic fans because the attic fan is designed to only remove the super-heated air from the attic.
Tim Carter from Ask the Builder says, "A typical whole-house fan moves vast amounts of air. The blades of the fan can be large, and they can have significant pitch so they can move thousands of cubic feet of air per minute. Turn one of these bad boys on inside an average-sized ranch home that has 2,400 square feet of finished floor space, and you can replace every bit of stale, hot inside air with cooler outside air in less than five minutes. These fans are designed to pull air through a house and exhaust the air into an attic space. They work best when they are operated in the early evening or night hours as outdoor temperatures start to nosedive and the inside air temperature of a house is still high. As outdoor humidity rises, the cooling effect from whole-house fans drops."
Carter also says you should open windows to let in the outside air and you may also need a separate attic fan and/or adequate attic ventilation to allow the air to exit the attic space.
According to The Natural Handyman, you should keep these things in mind:
1) Attic fans are economical to run when compared to central air conditioning. They can cool a house to outside temperature in a few minutes. Even in homes with central air conditioning, using the fan in the cool of the evening can cut your electric bill substantially plus refresh the air in the house.
2) Attic fans are not suitable for all climates or all people. If you live in a very dusty area or if there are high levels of pollen in the air, the attic fan will bring this pollution into your home as it exchanges the air. This is not good for folk with dust sensitivities, allergies, or even those who would prefer not to have to dust their homes often!
3) If your area is very humid, turning on the attic fan will bring this humidity into your home. This is not an issue unless your central air system has been de-humidifying your home all day. Under this circumstance, the "apparent" cooling effect is lost to the increase in air-borne moisture inside your home. In other words, even if the outside temperature is lower than the inside temperature, raising the humidity by turning on the fan will make it "feel" warmer inside!
4) Electrical skills are required for installation. Some fans have built-in pull switches, so you only need run one electrical wire to the fan. Since these fans draw a lot of power, especially when they are first turned on, they should be wired into their own circuit. This is an advanced electrical installation and should only be done by a qualified person. If you plan on doing this electrical work yourself, check the local electrical code requirements first and follow them 100%.
5) Possibility of back-flow of carbon monoxide from chimneys! If there are not enough windows open in the home, an attic fan may draw furnace exhaust back into the home right down the chimney, presenting a carbon monoxide hazard. Be sure windows are open whenever the fan is running and be sure there are carbon monoxide detectors throughout your home, especially in bedroom and near the furnace.
You should rely on experts to help you select the correct size system, the placement of the openings and louvers, whether it should be gable mounted or floor mounted, and the adequacy of your attic ventilation. Ask them about humidistat control or thermostatic control features, variable speeds, remote control, solar power, and any other "green" features that interest you. Ask for recommendations from the potential venders and check them out with the Better Business Bureau.
Because Michigan has cooler nights even during the warmer months, your home may be a good candidate for a whole house fan. You may see the annual energy bills for cooling your house drop from the thousands to the hundreds.
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