Easily installed and free to operate, solar attic fans are a smart choice for homeowners who want to save money cooling their homes in summer, prevent ice dams in winter, and extend the lives of their roofs.
Operating Principle
A solar attic fan uses photovoltaic panels to convert sunlight into electrical power. The electricity generated is used to turn a fan motor, exhausting air from the attic of a home.
Benefits
- In summer, temperatures in an unventilated attic can exceed 160 degrees F. A properly sized solar attic ventilation system will reduce attic temperature to 5-10 degrees F above the outdoor temperature. Ventilating the attic reduces the amount of heat transferred from the attic to the home, decreases the load on the air conditioning system (reducing your electric bill), and extends the life of the roof.
- In winter, heat trapped in the attic may melt snow on the roof, which trickles down and creates destructive ice dams in the colder eaves.
- The attic becomes warmest when the sun is the strongest. A solar attic fan runs the hardest when the sun is stronger.
- Everyday home activities such as cooking and showering create moisture which collects in the attic and promotes mold and mildew growth, reduces the effectiveness of insulation, and attacks the wooden attic structure. Year round fresh air circulation from a solar attic fan removes this moisture and fluctuations moisture related problems.
- Zero operating cost.
- Installation can be done by a handy homeowner. No electrician is required.
- Quiet operation.
Things to Consider
· The cost savings due to reduced air conditioner load depends on the price of electricity in your area, the amount of attic space in your home, the efficiency of your attic insulation, and the amount of ventilation your solar attic vent is able to provide. A typical installation will usually pay for itself in savings within 1-2 summers of use.
· A solar attic fan should not be used when air from the living areas of the home can freely enter the attic. This would result in conditioned air being removed from the home. Any openings between the attic and the home should be sealed before a solar attic fan is installed.
· Properly sized attic vents are required to allow fresh air to enter the attic and replace the hot air removed by the solar attic fan.
· Solar attic fans should be mounted away from ridge vents and gable vents.
Configurations
Solar attic fans are available three configurations:
- Self flashing roof solar attic fan: The fan base is flat and designed to slide under shingles and attach directly to the roof.
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Curb mounted solar attic fan: The fan base is a cap designed to fit over a curve which is attached to the roof.
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Gable fan: The fan exhausts horizontally through the gable end of the attic.
In addition, solar attic fans are available with fan mounted or remote solar panels.
Installation Overview
1) Cut hole in roof (South side is recommended), taking care not to cut through any roof framing members.
2) Slide unit under shingle
3) Reshingle around fan as necessary.
Commonly Asked Questions
1) What size fan do I need?
ANSWER: A solar attic fan should be sized to provide 10 attic air volume changes per hour.
To figure out what flow rate these works out to, figure out the volume of your attic in cubic feet. Multiply your attic volume x 10 air changes per hour to get the total flow required per hour.
Since fans are sized in terms of their cfm (cubic feet / minute) output, divide your total flow per hour by 60 to get cubic feet per minute.
Required flow rate in cfm = (attic volume x 10) / 60
Now check the fan specifications to find the fan or combination of fans required to meet your ventilation needs.
It is also very important to make sure there is enough air inlet area in your attic to allow fresh air to enter and replace the hot air being exhausted. A minimum of 1 square foot for every 360 cfm of exhaust is required. Typically soffit vents are used as inlets.
2) How long will a solar attic fan last?
ANSWER: Solar attic fans are designed to provide many years of trouble free operation. The length of manufacturers' warranties are a good indicator of the high standards these fans were designed to:
Attic Breeze Fans – Lifetime parts warranty
Solar Star Fans – 5 Year parts on solar panel and motor, 10 years on all other parts.
Natural Light Fans – 25 Year parts warranty
SunRise Solar Fans – 5 year parts warranty on motor, 10 years on all other
3) How is a solar attic fan controlled?
ANSWER: A thermal switch is often used to control a solar attic fan. This switch only allows the fan to run when the attic is warmer than 80-90 degrees F. Running the fan only when the attic is hot extends the life of the fan motor and results in less heat loss to the attic in winter, but does not allow the fan to reduce moisture build-up in the attic at all times and does not allow the fan to prevent ice dams during the winter.
