With the flip of a switch, a whole-house fan pulls cooler outside air through open windows and sends hot indoor air out through the attic. It can lower the temperature in your home by five degrees in just a few minutes.

Inexpensive energy-saver

One of the biggest advantages of a whole-house fan is the cost - only $150 to $350, compared to thousands of dollars for a central air conditioner. And when used in place of a central air conditioner, it can lower your cooling costs by 30 percent.

Installing a whole-house fan can be a do-it-yourself project if you have some home-improvement experience in wiring, and you have adequate space in your attic. If not, you can hire an electrician or handyman to install it for you.

Use alone or with an air conditioner

You can use a whole-house fan as a cooling system by itself, or you can combine it with your central air conditioner to help cool the house more quickly.

Factors like outside temperatures and humidity levels can affect how well a whole-house fan works. A good rule of thumb is to use the whole house fan when outside temperatures are below 85 degrees.

When the temperature climbs higher than that, or if the humidity level is uncomfortable, it's more effective to use your air conditioner.

Choose the right size

To gauge your cooling needs, multiply your home's square footage by three to calculate the cubic feet of air moved per minute (CFM).

To calculate the required vent space, divide your CFM by 750 - this gives you the number of square feet of attic vent space needed. If your vents are screened or louvered, double that amount.

Allow for good airflow

When you're using a whole-house fan, it's important to allow for good airflow - make sure you leave a window or door open to keep the air moving and avoid damaging your system.

It's also important to insulate the fan opening during the winter - the louvers don't seal tightly, making it a prime place for heat loss.

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