Solar Attic Fans: Facts and Advice

A solar attic fan will reduce heat build-up in your attic and can minimize the load on your HVAC system. Available for all roof types, a solar attic fan can be installed easily and blend seamlessly into your roofline.

Two Problems

Heat and moisture are your attic's worst enemy. The solar attic fan is an environmentally friendly way to cool and protect your attic and roof.

During the hot summer months the temperature in your attic can exceed 160°.

The attic acts like a giant radiator, passing excess heat back into your living spaces and driving temperatures and cooling costs through the roof.

No matter how much insulation is in the attic, heat can still transfer into adjacent living spaces. In fact, extra insulation can actually add to temperature increases because heat is trapped in the insulation. Proper ventilation evacuates this excess heat build-up.

Heat is not just a problem during the warm parts of the year. During cold winter months the heat trapped in your attic can melt the snow that accumulates on your roof. As the water trickles down, it refreezes at the cooler eaves, leading to destructive and costly ice damming.

All year long trapped moisture wreaks its own brand of havoc. Everyday activities such as showering and cooking produce water vapor that migrates into the attic. Even with the use of vapor barriers to keep moisture from entering the attic, there are air leaks around ceiling light fixtures, bathroom exhaust fans allow unwanted moisture into the attic.

This moisture promotes the growth of mold and mildew and, if it saturates your insulation, can lead to fungal decay and destruction of your roof frame.

Small, passive roof vents are often woefully inadequate at dissipating this heat and moisture and electric fans require wiring and will increase your electric bill.

By using the Solar Attic Fan, your attic will be cool, fresh, and dry.

How Does A Solar Fan Work?

Basically, a solar attic fan consists of a mounting bracket (see installation video below to see what’s involved), a fan and solar panels to power the fan.

The solar panels can be either included as part of the fan - or attached separately. Here are three solar attic fans available through Amazon.com that have gotten high ratings from users:



Benefits of Having A Solar Attic Fan

1. Reduce HVAC costs: The key to proper attic ventilation is to create continuous air circulation throughout the attic space while preventing moisture from entering. In an ideal venting system, air should enter the attic from the eaves or soffits and escape outside at the roofs ridge.

If you've ever been in your attic, you know just hot the space can get, especially in summer months. The sun beats down on the roof surface and heats up the stagnant air inside the attic.

Building codes require homes to have a passive vent system. But, passive ventilation does not provide the pressure needed to force the air through the attic and outside. That's where a motorized fan comes in.

An attic fan placed at the roofs ridge will pull air in from outside, force it to move through the entire attic space and escape through the attic vent. In summer months, a solar attic fan can reduce the temperature in an attic by up to 40°F!

As the heat is exhausted, the workload required by the air conditioning system in your living space areas is reduced, thereby saving energy and extending the life of your air conditioning system.

In the colder months attic insulation is less effective when “damp” causing your furnace to produce more heat longer. A solar attic fan helps keep the insulation dry, thus reducing your furnace costs in the winter.

2. A Solar Attic Fan Extends The Life Of The Roofing Materials: Ask any roofer and they will tell you most roofing material (asphalt shingles and cedar shakes in particular) is built to withstand the intense heat generated by direct sunlight. But when they are also baked from underneath by a 150 degree attic, which is just what happens in an under ventilated attic, they don’t last as long.

Attic ventilation is also required in cold environments because hot moist air lingering in the attic spaces can condense on the underside of the roof sheathing and rot it out and also causes mold to develop on the interior walls.

The combination of excessive heat (top and bottom) and moisture buildup lead to higher roofing costs over time.

This is why asphalt shingle manufacturers warranties require proper attic ventilation

NOTE: A good indicator of a moisture problem is rusty roof nails sticking through the roof deck.

3. Solar Attic Fans Operate Using Free Solar Energy: A solar attic fan is a simple way to add a motorized venting system to your home without needing any extra electrical wiring or structural changes.

As a general rule, when a solar panel heats up, it becomes less efficient at converting light into energy. To combat this fact, the solar panel can be mounted in a raised position. Raising the panel off of the housing reduces heat build-up and provides increased air circulation resulting in better performance. The solar panel mounting bracket allows for an envelope of cool air to continually circulate around the entire solar panel.

For more information about Natural Light Solar Attic Fans, which mount their solar panels in a raised position click here.

4. 30% Federal Tax Credit: Keep in mind when you file taxes online that the Federal Tax Credit for solar attic fans has been extended through 2016. A solar attic fan is eligible for a 30% (up to $1,500) credit on the purchase price of the fan, installation and sales tax.

How do I determine the correct sized fan for my attic?

While some manufactures size their fans for a certain number of square feet, we know that is just a guideline. Square footage measures the approximate size of the floor of the attic and doesn’t take into consideration the volume or cubic feet of air in the attic.

Then there’s the climate (Arizona vs Maine) and the construction of the building (brick vs wood) and even the color of the roof. After all that, the real answer is “more ventilation is generally better”.

  • The SRS-850 (850cfm in full sunlight) is specified for up to 1,200 sq ft. This unit has an 11 watt solar panel. It can be used over a garage, in a small attic or as part of a gang of fans in a large attic.
  • The SRS-1050 (1,050cfm in full sunlight) is effective for attics 1,200 to 1,600 sq ft. This unit has a 15 watt solar panel and is our work horse fan; the one that we put on most single-family dwellings. Sometimes you need to use two of these if the attic is especially voluminous or has several sections that don’t connect well.
  • The SRS-1250 (1,250cfm in full sunlight) is what we recommend for large attics or for commercial applications. This unit has a 20 watt solar panel and may be the most efficient of the SunRise Solar fans.
For more information about which size you should consider check out this solar attic fan venting capacity and sizing chart.

Where does the fan sit on my roof?

The typical installation is on the South or West face of the roof where the sunlight is most direct. If that turns out to be on the front roof - then we like to double check to make sure the owners are ok with that. In actuality, most of the time having a fan on the front is not an issue. If it is, it is possible to install a remote solar collector (the fan can be mounted on the back roof and a much smaller cable-connected solar collector slips onto the sunny front with a much thinner, less noticeable profile).

Case Study #1: U.S. Sunlight's Solar Attic Fan and Controller Win Best Sustainable Product Award

Recently the US Sunlight solar attic fan and controller was selected to help cool the US Treasury building. To see the video: click here.



Case Study #2: Natural Light Solar Attic Fan



Natural Light Solar Attic Fans are manufactured using high-impact photovoltaic solar panels to power the fan for free all during the day. The units are fully operation right out of the box and install in less than an hour.

The Natural Light Solar Attic Fan is designed with an exclusive adjustable bracket allowing the solar panel to be positioned at various angles for optimal solar exposure. This adjustable solar panel bracket system maximizes the sun exposure on the solar panel no matter if the unit is installed on a flat, standard pitch or steep roof.

Additionally, Natural Light offers an optional special order remote solar panel that is installed away from the attic fan housing. It is used on applications where there is limited sunshine available to the installed unit. The remote panel is installed in a sunny area, capturing the maximum amount of sunlight and therefore achieving optimal attic fan performance.

The Natural Light Solar Attic Fan was precision engineered to minimize obstructions in the fan housing to increase air flow. It incorporates an angled throat to facilitate a Venturi or suction effect which increases cfm output and also reduces wear on the motor.

Installation

We recommend you hire a competent roofer or someone accustomed to working on roofs to install your fan. Instructions are on and in the box. A trained roofer can install them safely and leak-free in about 45 minutes … cedar and very steep roofs take longer. $100 to install the fan would be a safe estimate.

Solar Attic Fans operate best on a South or West facing roof. If that roof is on the front of your house, SunRise Solar makes a remote collector. That means that the smaller solar collector panel canbe mounted on the visible roof face, but the fan itself could be mounted almost anywhere it might not be as obvious.

To see an example of how one of these fans can be installed, check out this video.

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