Whole House Fans are an Alternative to Air-Conditioning

What about Whole House Fans?

There are two types of attic fans, one cools only the attic and is properly called an attic fan, the other one is really a whole house fan and cools the whole house using outside air instead of air conditioning. Whole house fans are an alternative to air-conditioning. Both fans can be used with satisfying results.

Whole House Fans are an Alternative to Air-Conditioning

Many people use whole house fans are an alternative to air-conditioning. A whole house fan is most effective when outside air temperatures are below 82ºF. It brings a cooling breeze in through the windows of the home and cools more efficiently than an air-conditioner. Some times central air-conditioning is too expensive to install. When a house has been originally built with hot water radiator heat, installing central air-conditioning can be cost prohibitive because there is not any duct-work to distribute air throughout the house. Also,  a whole house fan only uses about ¼ of the power that a central air-conditioning system does. Some people just don’t like air conditioning or may want the option of using outside air for cooling and ventilating their homes. Whole house fans draw massive amounts of air through a home. Moving air feels cooler than still air so high volumes of air are usually preferred.

One objection that some people have with whole house fans is the sound that is created when running. There are basically three types of noise created: air noise, motor vibration and shutter rattle. A well-engineered whole house fan will address all of these issues.

Generally speaking the more blades a fan blade has the quieter it will be, (five blades are better that four). Each blade does less work and thereby creates a smoother, even sound as opposed to fewer blades where the sound is choppy and irritating. One strategy for sizing a whole house fan for a house is to get the largest fan that will fit into the ceiling area of a hallway where a fan would typically be installed. Any size fan will be quieter when run at a slower speed; so by getting a large fan that has a low speed you can get less noise and still move a high volume of air because of the large size. Running on low speed also creates less wear and tear on the fan and saves electricity. Better whole house fans will have the whole fan isolated from the homes framing with foam strips or rubber mountings that will not transmit sound into the framing of the house. This keeps the motor hum from resounding through the framing and drywall of the home. It is better to have no direct mechanical connection to the house framing. Heavier fans are better because they rest on foam weather stripping held down only by their own weight.

Higher quality shutters will be heavier and have connecting rods connecting vanes of the shutter so they act together. This prevents one or more vanes from oscillating and possibly clapping shut and re-opening. Also, a better shutter will have an adjustable spring that will assist in opening the shutter as the fan sucks it open and cushion and slow the closing when the fan is shut off. This prevents the shutters from creating a loud thump when shutting when the fan is turned off. Some shutters even have a felt strip at the edge of each vane to seal in air when the fan is off and to silence the shutter when it closes.

Having a timer is also a good idea. A timer will let the fan run a pre set length of time so that you can set it before going to bed an have it shut off automatically when you feel it may get too cold at night. Thermostats are not a good idea because they could turn the fan on when no one is home and preparation hasn’t been made for it to come on. Windows must be opened first. Also, a fire in the fireplace could trigger it to come on unexpectedly with danger of sucking flames in from the fireplace. Obviously, some caution must be used when operating a whole house fan.  The drill is really pretty simple: turn off heating and air-conditioning, open windows, no fires in fireplace and then turn the whole house fan on. Without opening windows first, some air could also be drawn down other vents or chimneys for heating and water heat, possibly blowing out pilot lights.

The amount of work required to install a whole house fan varies from house to house, but can generally be retrofitted into an existing house by a professional in about 8 to 16 man-hours. One major variable is the venting, if you plan on running the fan on high speed, (most people do) you need to make sure that there is at least enough exhaust venting for high speed setting. Fans are rated by cubic feet of air per minute or cfm. A good rule of thumb is to provide one square foot of net free venting area for every 750 cfm. Net free venting is the area after subtracting for louvers and screens. Generally the vents are roof vents, louvered wall vents or eave vents. Some roof vents and some eave vents have their respective net free venting areas stamped right on them. Ridge vents, depending on type, are not as good for providing the bulk of vent area needed although they do help slightly.

One strategy is to get an attic fan with a whole house fan. Special timer switches (DPST) are available and when installed they will turn on both fans to help expel some of the air being pushed into the attic. It is important to use only this type of switch for this application, because with a normal switch the attic fan thermostat would back feed and run the whole house fan even when the homeowner has not selected the on position for the whole house fan switch.

Better whole house fans have a welded frame. Effectively they are one-piece construction using heavy gauge steel for the venturi and motor and fan supports. This type of construction is better because it will never loosen up or begin to squeak. The only problem might occur if the installer was trying to fit the fan into a very small attic space; it may not fit through the opening when turned up on end before hitting the roof. Fans that can be disassembled can be fit through and then reassembled in the attic. One strategy for installing a welded frame fan into a smaller attic is to use a larger shutter than is required so the fan could be lifted into the attic in a horizontal or flat position and then supported by ledger strips around inside of opening. The larger shutter would then fill the larger opening that was made in order to lift the fan through in flat position.

Whole house fans are an alternative to air-conditioning so do not plan on using it together with your air- conditioning or you would loose all that cool air you just paid for. There’s nothing like a hurricane of fresh air on a summer night!

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