Solar-powered attic fan


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Old 08-29-09, 10:11 AM
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Solar-powered attic fan

I am planning on installing two solar-powered attic fans (each will handle 1200 sq/ft) and was interested in whether people have had any good/bad experience with these. I am looking at these because the government is offering 30% tax rebates.
 
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Old 08-29-09, 12:49 PM
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Solar-powered attic fans rely on a small solar panel (typically 10- or 20-watt) to power a DC motor. The fans are installed with intake vents to provide high-capacity powered ventilation without electric operating costs. Most vents are mounted high on the roof near the ridge and are combined with soffit vents located at the roof overhang or gable vents located on the building walls near the roof peak for balanced intake and exhaust airstreams.

The pluses are that they work for free, using the sun's rays, they exhaust hot air and they don't require a separate power source. The negative is they work only when sunlight hits the solar panel. If a cloud drifts by, blocking the sun, the fan stops. Worse, as the sun moves through the sky, eventually contact with the solar panel is lost and the fan stops. At best you'll get part-time cooling.

The hard-wired version is thermostatically controlled to kick on when the attic reaches a certain temperature. True, they do use electricity from the grid, but usage is minimal. The bottom line is that you'll exhaust hot air when you need to regardless of the vagaries of sun and cloud movement.
 
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Old 08-30-09, 04:32 PM
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What is the size of the attic footprint?? Are you planning on sucking out all the insulation with the fans??? Attics do not require and air change every 30 seconds. As for being free, they are far from free. Installation costs are essentially the same, but thermostatically controlled fan are less expensive. I would say it is a wash over a period of time. As for the tax deduction, it is 30% of the cost of the material(not total cost), up to $1500. Personally, I would not even figure that into the equation.
 
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Old 08-30-09, 05:45 PM
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Old 08-31-09, 06:41 AM
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You Need Ventilation AFTER Sun Goes Down

Two thoughts:

First, a 14" wind turbines pulls as much air as (800cfm) as most solar fans with an average 8mph wind. And they work 24/7 to remove heat and moisture year round. A 14" wind turbine is only about $50 bucks and installs in about 10 minutes.

Second, your insulation acts like a big sponge and "holds" heat too. When the sun goes down you want ventilation to help pull the heat out. Otherwise, it acts like a big, hot blanket on your ceiling and will continue to transfer heat into the home. You want to get the insulation moving towards ambient temperature as fast as possible.
 
 

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