Most of the attic power vents are controlled by a heat or humidity sensing switch and can become active / cause injury while you’re performing maintenance.
Humming, muffled noise coming from above the ceiling during the summer is most likely an attic power vent, working hard to pull out hot air from under the roof (attic power vent should be placed close to the roof ridge – top, or installed as a gable vent).
The most common installations include adjustable thermostat and in some cases humidistat, which activates attic power vent motor accordingly with your preferences (once set, it operates automatically responding to temperature or / and humidity changes).
There are also some devices preset by the manufacturer (usually between 85F – 100F), and attic power vents with no sensor at all, controlled by on/off switch mounted in various location (usually close to the attic entrance).
To serve its purpose properly and save instead of wasting your money, certain requirements for attic power vent installation have to be met:
There must be other, adequate number (or more likely square footage area) of ventilation ports installed in lower section of the roof, they are called: soffit vents, if your house roof has an overhang, which extends beyond the house exterior wall, or gable vents – located at the attic area, commonly on the exterior wall where the two planes of a sloping roof join, forming a triangle.
There’s a possibility, that type of your roof allows only for installation of vents on its surface – good examples are hip roofs on many of the Chicago style Georgian type homes, which have no overhang / soffits.
In such case, if the attic power vent has been installed in upper section of the roof, passive vents can be placed not less than 1/3 of the distance between the roof bottom edge and top (ridge), hip / ridge vent system can be installed – click here for details , or vented drip edge mounted along the roof edges.
The attic floor, and all penetrations between the attic and living area of your house should be properly insulated and sealed. Any gaps, holes, and lack or inadequate number of attic vents will cause attic power vent to create a vacuum, and remove AC cooled air from the house. In some properties, there’s a duct between the attic and utility room, which provides combustion air for gas burning appliances – this one must remain open on both sides (on the picture)!
However, some of the larger animals are strong enough to penetrate this obstacle, in the process damaging fan blades. Therefore, it’s a good idea to examine your attic periodically. Be careful, most attics have no flooring installed and walking on framing is difficult, if possible, examine fan condition from attic access point.
Before installing a new attic power vent in your attic, make sure you properly calculate square footage area (calculator 1 : calculator 2). If installed fan is too small, it will have to operate much longer, to move the same amount of air through the attic. Adjusting thermostat too low might cause fan to run constantly during hot summer – try to set the temperature dial to a 100 -110 degrees Fahrenheit.
The fan should start automatically as soon as the attic temperature rises above the preset setting, and cuts off when the attic is cooled down to approximately 10% below the thermostat setting.
Go Green and try low voltage, solar battery operated attic power vent – saves money on installation, very quiet, but approximately 3 times as expensive, as a regular attic power vent. Watch the video below for more details about the Solar Powered Attic Fan from U.S. Sunlight Corp.
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This article was written by Dariusz Rudnicki
I'm a retired Illinois home inspector, founder and editor of checkthishouse.com, a blog which attracts around 2 thousand readers daily and is dedicated to answering the many questions of home owners and home buyers. Connect with me on Google+ Find me on Google+ Local