Week of September 11, 2006
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Ventilating a Breeze With Solar Attic Fans

Now available from many manufacturers as an affordable alternative to conventional fans, solar-powered attic fans cost nothing to operate and can help reduce summertime cooling loads while at the same time providing ventilation without added utility cost, according to ToolBase Services.

The solar-powered fans rely on a small (typically 10- or 20-watt) solar panel to power a DC motor when the sun is shining, says ToolBase. The fans, which exhaust air at a rate of 800 to 1,200 cfm, are installed with intake vents — such as soffit and gable vents — to provide high-capacity powered ventilation without electric operating costs.

Most vents are mounted high on the roof, near the ridge, and combined with soffit and gable vents for balanced intake and exhaust air streams. Solar-powered gable ventilators are also available.

The fans are easy to install. In new construction applications, roofers will usually install powered ventilating units. The solar units eliminate the need for an electrician to rough and finish wire the units. For retrofit projects, a roofer or do-it-yourselfer can install a solar-powered fan using conventional materials, tools and techniques.

Units typically come fully assembled and are self-flashing. Most manufacturers offer clear installation instructions, often with diagrams and pictures. Powered attic vents are designed to be used in conjunction with sufficient intake air vents, such as soffit or gable vents. Units can typically be supplied and installed by a roofing contractor.

The fans retail from about $350 to $600 depending on ventilation capacity, manufacturer and optional features of the unit, such as a thermostat.

Although the solar equipment costs about $200 more than conventional powered fans, it does not need electrical wiring, which closes the gap on the cost of the installed product.

Because the fan motor is powered by sunshine, the highest fan speed typically coincides with the time when attic ventilation is needed the most.

ToolBase warns that if there is inadequate attic intake air and poor sealing between the conditioned space of the home and the attic, powered attic fans can potentially draw air from the house into the attic. This can compromise energy efficiency, increase the risk of attic moisture problems and increase the risk of “backdrafting,” in which the byproducts of combustion are drawn into the house.

The International Residential Code specifies the amount of ventilation required for attics in newly constructed homes. The required vent area can be reduced with installation of a ceiling vapor barrier or ventilators located in the upper portions of the space to be ventilated. The code does not require powered ventilation for attics.

There may be difficulty using solar attic fans in Dade County, Fla. and areas where building products must be approved by the inspection department. The concern in high-wind zones, such as coastal Florida, is that roof penetrations of any sort provide a potential weak point in the building envelope. High winds can blow away protrusions, leaving the building susceptible to damage from the rainwater that accompanies the wind.

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