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What Is An Attic Fan?
Why Should I Install an attic fan?
How to Determine Which Size Attic fan is Required?
What Is An Attic Fan?
The phrase "central heating" is commonly heard and understood. An attic fan is basically a central ventilating system having three major components.
First comes the unit itself. This unit consists of the fan blade and its electric driving motor; an opening in which the blade revolves at slow, quiet speeds, and the necessary framework, shaft and bearings for mounting these parts. Fan units are made for both horizontal and vertical discharge, and will be described.
Since the fan unit is usually located in the attic and it is desired to draw fresh air into the house through the doors and windows in the lower floors or basement, the second essential is an opening between the living quarters of the house and the attic, through which the fan can draw this cooling air. This opening is usually located in the ceiling of the upper floor of the house, often directly under the fan unit in the attic. A grill which will match with the interior trim of the house or a suitably framed automatic shutter should be inserted in this opening.
Once the fan has drawn air through the house and up into the attic it must exhaust this air to the outdoors. If there are not sufficient ventilating louvers or windows already in the attic walls, an outlet louver of some type must be provided.
When the attic fan is in operation, fresh air enters through any door or window which is opened. Therefore, the entire house may be ventilated equally, certain rooms may be closed off from ventilation, or ventilation may be concentrated in one or two rooms depending upon which windows and doors are opened or left closed. For example, in extremely hot weather it is often desirable to have the fan draw all its air through the one or two most used rooms in order to create a strong cooling breeze, rather than have a gentle circulation of air thought the entire house.
During the winter months, the attic fan may be operated when needed to exhaust cigarette smoke or unpleasant cooking odors from the house. One or two minutes operation are all that is necessary to completely freshen the air throughout the house without chilling.
Poor Attic Ventilation Can Ruin Your Insulation, Destroy Your Shingles, And Raise Your Energy Bills!
Why Take Risks?
It is estimated that 9 out of 10 homes in North America do not have proper attic ventilation. Why? Because most people are unaware that attic ventilation can impact the longevity of their entire home!
For example, in the summer, an improperly ventilated attic can cause heat to build in excess of 160°F. This superheated air eventually penetrates the ceiling insulation into the living area below.
Types of damage that can result include:
. Premature aging of your roofing system ("fried" shingles)
. Warping, cracking, or breaking down of wood framing
. Damage to siding, exterior or interior paint, and wallpaper
. Higher energy costs
A properly ventilated attic can help reduce the load on your air conditioner by moving the superheated air out of your attic before it builds up and causes damage.
In the winter, various household appliances, bathtubs, showers, and cooking vapors can contribute to excess moisture build-up. Improperly ventilated attics will allow this moisture to collect and cling to the underside of the roof. There, it will condense and fall, soaking the attic insulation and reducing its efficiency.
Additional structural damage can include:
. Roof deck warping and rotting of the wood frame
. Mildew growth
. Buckling of shingles and felt
Finally, attics should be properly ventilated to help prevent ice dams in cold northern climates. During the winter, ice and snow on a roof will melt and run down the deck to the cooler eaves. This run-off can re-freeze, creating an ice dam that will trap moisture on the roof. The moisture can eventually back up under the shingles and enter your home - causing hundreds or thousands of dollars of damage to your ceilings and walls. Adequate attic ventilation will reduce the amount of initial melting that occurs on your roof, thereby reducing the chance that ice dams will form. |
Proper Attic Ventilation
Proper attic ventilation systems allow a continuous flow of outside air through the attic (see illustration
at left), protecting the efficiency of the insulation and helping to lower temperatures in the living space.
It consists of a balance between air intake
(at your eaves or soffits) and air exhaust
(at or near your roof ridge).
The FHA (Federal Housing Administration) recommends a minimum of at least 1 square foot of attic ventilation (both intake and exhaust) for every 300 square feet of attic space. For example, if your attic is 900 square feet, you need a total of 3 square feet of ventilation. This amount is generally divided equally between intake and exhaust ventilation (i.e., 11/2 feet of each), to insure proper air flow through the attic. |
Why An Attic Fan Should Be Installed
Why ventilate the attic? For very good reasons! The hot summer sun, beating down on the roof of the average home, makes a veritable furnace of the space under the roof. Unless some means of dissipating this heat is provided, it radiates down through the ceiling into the rooms below. Long after the sun has set and outside temperatures have dropped many degrees, these rooms continue to receive this accumulation of heat.
The dark, composition roof coverings used on over two-thirds of the homes built today absorb a greater amount of the sun's heat than did the wood shingles used in the past century. While insulation retards the downward flow of this heat, it cannot prevent uncomfortable temperatures in the rooms below. And unfortunately, though insulation is an asset to every home, it is as effective at holding heat inside the home in summer as it is in winter. Natural ventilation of the attic space cannot keep pace with the heat load being absorbed by the roof.
As summer progresses, there is an increasing accumulation of heat in the roof, beams, attic, walls and furnishings of the home. While it is true that some lowering of temperature of the home occurs during the night, summer nights are too short to allow for anything like an equalization of temperature.
Therefore, forced ventilation! An attic fan or whole house fan provide a ready means of dispelling this heat, and not only that, it draws gentle breezes throughout the house whenever and wherever the home owner wants them. By the simple touch of a button, cooling breezes are wafted in through the windows, sweeping the heat and stagnant air up through the attic and out of the house. With an attic fan, the calm breezeless nights which weather bureau records prove to be the rule in many sections of the country, hold no threat of discomfort, no risk of tossing, sleepless nights.
More or less ventilation for the rooms of the average home is a simple matter of opening or closing doors and windows. At left, the entire house is being ventilated. At right, the closing of a hall door has made the entire capacity of the fan available for cooling the bedrooms.
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