Solar Attic Fans: Pros and Cons
- Studies show a reduction in attic temperature of 30% and AC usage of 6%
- Solar-powered with zero greenhouse gas emissions
- Increase comfort in hard to cool attic spaces or other rooms
- Very positive consumer reviews
- Easy installation (less than an hour typically)
- Financial payback may be limited depending on electricity prices and the cost of the unit
- Potential risks due to backdraft of appliances fumes (e.g. natural gas heaters)
- May be more attractive alternatives to reduce AC costs
- They do not have a battery – so they do not run during cloudy days or at night.
- For 100% power, the solar panel must have 100% sun on the solar panel. As the sun sets, you lose power.
** Lastly, another concern mentioned by several opponents of solar attic fans is that flue gases from appliances such as a natural gas water heater can be backdraft into the house. This is a real concern and potentially dangerous, so should be analyzed by a professional if you decide to install a solar attic fan.
Important not to mix Solar fans with any other type of ventilation. Like a river, airflow will take the least resistance. This means passover-type vents will act as an intake pushing the hot attic air down back into your attic and possibly into your home.
Source: Florida Solar Energy Center
An attic fan works by pulling warm air out of the attic to allow for cooler air to come through the gable or soffit vents to reduce the air temperature in the attic. By reducing the air temperature in the attic, cooling demands in the rest of the house can be reduced. Proponents of attic fans also claim that a more moderate attic temperature can also extend the life of roofing materials, although that is harder to prove and more likely driven by the UV exposure of the roof.
A solar-powered attic fan does just want the name implies – these are attic fans with attached medium-sized solar panels. When exposed to sunlight during the day, the panels will generate electricity to power the DC motor in the unit and turn the fan. Although they only run on solar during the day, some units can be connected to batteries to run at night. So the solar-powered units provide the same benefit as a normal attic fan but have zero costs to operate.
How Many Solar Attic Fans Do I Need? Important Measurements
Solar attic fans’ ability to move air is measured in cubic feet per minute (CFM) and a good rule of thumb that manufacturers use is that 1,000 CFM can handle a 1,600 square foot attic (1.6 square feet per CFM). Most of the models that we reviewed could handle more than 2,000 square feet, which should cover most attics.
The other important measure is the wattage of the panels, which are measured in watts and based on standard operating procedures. So be aware that if your roof does not have adequate sun exposure, you may not generate enough power to run the fans. Check out the solar radiation in your area using the Department of Energy’s database.
Velux fixed skylight models are cheaper than acrylic. Custom glass skylights cost $400 – $900 more than custom acrylic skylights.
Glass skylights have a near-perfect transparency rating. Acrylic by its nature, can add a wavy distortion to the view and is usually tinted bronze.
Glass has factory seals that are warranted for twenty years by the manufacturers.
Acrylic needs to expand and contract from thermal expansion and this wears out the gaskets that hold the acrylic dome in its frame. And acrylic will yellow and get brittle over time.
Tempered glass tends to survive punishment better than acrylic. Glass has to have its edges protected inside a sturdy frame and can survive most hailstorms. Acrylic will not hold the same weight as glass can—think snow load.
Acrylic skylights use 1980’s design technology. The better ones will have thermal break (which separates the interior and exterior thermally) aluminum frames, however, glass has much better thermal insulation standards in every skylight.
Manufacturers of acrylic aluminum-framed skylights drill holes in their condensation gutters to allow the water to weep out. However, this lets cold air in and causes condensation. Velux skylights are 21st-century technology so you don’t have to worry about heat & cold transfers or condensation.
Glass is flat low to the roof, giving a streamlined look, while domed acrylic skylights stand out and look outdated.
Glass is much better insulated and reduces unwanted outside noise by up to 50% less than an acrylic skylight.
Velux skylights come with Neat® glass coating to keep your skylight cleaner longer, leaving the surface virtually spotless. Acrylic requires regular cleaning and care to ensure long-term usability.