Q&A /

Whole House Fan Sizing

DEAR TIM: I take a whole house fan located in the second floor hall ceiling of a business firm I just purchased. The fan and louvers look new and seem to operate smoothly, but the fan doesn't seem to exhaust very much air. I have seen these fans operate in other houses very effectively. What could be the trouble? Laurie B., Beavercreek, OH

DEAR LAURIE: I detest to be the bearer of bad news, merely you may have several issues. Fortunately, they are quite simple to diagnose. The effectiveness of a whole house fan depends upon several key setup features. Everything must be just right, or the fan will non operate properly.

Whole firm fans are work horses. They are designed to motion great quantities of air. That is why they are able to provide comfort during periods of hot conditions. The chief by which they operate is extremely simple. During the daytime, the air inside of your house gets hot and stale.

whole house fan

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Mostly speaking, afterward sunset the air temperature outside of your house is lower than the air temperature inside. A whole house fan pushes the hot air out of your business firm and replaces it with the cooler, outside air.

Air movement creates a cooling effect by increasing the charge per unit of evaporation from your pare. The faster that perspiration evaporates, the libation y'all will feel. If you can completely replace the air inside of your house every two minutes, you should experience this cooling effect.

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Because houses come in a variety of sizes, whole house fans must be fabricated to suit the different volumes of air. The force or power of a whole house fan is measured by the amount of cubic feet of air per infinitesimal (CFM) that information technology can push button. These ratings are ordinarily in the range of thousands of feet per minute.

There is a unproblematic way to make up one's mind the size fan you need for your house. Assuming you have standard eight pes ceilings, simply multiply the total square footage of the finished living infinite of your house by three.

This number represents the minimum cubic feet per minute that the fan must button. Simply purchase a fan that has a CFM rating equal to or greater than the number you lot calculated.

At that place is one other major consideration. These powerful fans must exist able to easily push the hot air out of your business firm. They require openings in the roof or gable ends of an attic space to do this.

If these openings are non large enough, the fan will spin ineffectively. For every 750 CFM that the fan is rated, you lot demand a minimum of ane square foot of gratuitous open exhaust area. Beware, insect screening placed over these openings can significantly reduce their free exhaust expanse. Many louvers and roof vents are stamped with a rating of their free open up exhaust expanse.

Now, let's solve your problem. Commencement, check to see if you take the right size fan for your house. Then, check to meet if the exhaust areas in your cranium are big enough to handle the CFM capacity of the whole house fan. If your fan is chugalug driven, make certain that the chugalug is adjusted to the proper tension.

Based upon the model number of your fan, check to see if it is a multi-speed fan or variable speed. Mayhap your fan was operating at its lowest speed when you checked it. By the style, did you have several windows or doors open up when you lot turned the fan on? Think, you have to provide the fan with a readily available and aplenty supply of replacement air.

Author'south Notes

February, 1999

At that place are new variations on the traditional monster attic fans. You can now buy quiet dual bract fans that operate at lower CFM rates - up to 1,000 CFM - and however do a very expert job of moving air through your home. These fans have insulated doors too.

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