We had just completed the installation of the solar panels on our roof, when we stopped by the San Jose Home and Garden Show. We had thoughts of looking for a landscaper for our next project, dealing with the jungle that is our backyard. Instead we ended up ordering a jacuzzi and signing up for a Solar-Powered Attic Fan from Solatube.
An attic fan is a fan placed near the peak of the roof to draw hot air out of the attic. Just as in a car in the sun with the windows all closed, the air in an attic can reach 150F in the summer. This makes the air condtioner work harder because it has to fight against the heat from above. The attic fan pulls the hot air out of the attic, pulling outside air in through the soffit vents, cooling the attic, and reducing the need for air conditioning. Since the temperature had recently been in the 90s, this was on our minds.
An attic fan is also supposed to help in the winter, though I don't know how true that is in this part of California.
A solar attic fan is an attic fan that runs on electricity generated from sunlight. Besides not having to plug the fan in anywhere, the benefit is that the fan automatically turns on when it is needed the most, when the sun is shining. The Solar Star fan we got has a 10 watt solar panel built into it, but you can get one with a separate panel, if the place you want to put the fan doesn't face the sun.
We happened to have the perfect place for it on the SSW facing roof above the newly installed solar panels, near the ridge line. As with the other solar panels, you get the most power (in the northern hemisphere) when the panel is facing south. However, since in the morning, there is usually cool air in the attic from the previous night, you want the fan to run more in the afteroon, so having the solar panel face southwest or SSW would be better. You want the fan as high as possible for the best effect. Our fan pushes up to 800 CFM (cubic feet per minute) of air, which they say is appropriate for an attic of up to 1200 square feet, just the size of our house.
Shortly after visiting the home and garden show, I was busy with several trips. When I got back from those, I wondered why we hadn't gotten a call from the installers at Renaissance Builders to set up an appointment. Maybe the TeleZapper attached to the phone scared them off. It wasn't until the temperature reached 98F again in mid-September that I got motivated to call them up to get an appointment for installation within two weeks. Installation was the quick 20 minutes that they promised. A hole was drilled through the roof, the fan installed and screwed down, and the edges all sealed to keep the rain out.
It was neat seeing the blades of the fan turning, driven by the electricity from the solar panel, as the installer walked toward the house with the fan. One hot day after the fan was installed, my sister visited and was astonished to hear we had not had the A/C on at all that day. So it works. Despite the brochure saying the fan should reduce heating costs, I wonder if in the San Francisco Bay Area, if it will actually increase our heating costs. On the rare clear cold night followed by a sunny clear day, it feels a bit colder in the house. But since the heater only turns on for 20 minutes a day in the morning, just enough to get me out of the bed and into a hot shower, I figure it's not a big deal.