In a perfect world, you wouldn’t need an attic vent. The roof plane would be insulated and air-sealed, and attic heat buildup wouldn’t be an issue. But it’s not a perfect world and attics in most homes are either uninsulated or poorly insulated and nowhere near airtight. On a sunny day, the roof transfers heat to the attic and ultimately into the conditioned spaces below, putting a strain on the AC system.
iSolar Solutions claims it can solve this problem with its Solar Attic Fan, which is designed to replace the innards of existing passive roof vents, but which contains a fan powered by a small solar array. The fan speed is calibrated to the electrical output of the solar panel so that the stronger the sun is, the faster the fan runs, to a maximum of 400 cfm.
The argument against powered roof vents is that they create negative pressure, which draws more warm air into the building and conditioned air into the attic, both of which increase the AC load. But the manufacturer claims that the Solar Attic Fan is “right-sized,” and independent testing by Building Knowledge Canada supports that, for two reasons: The fan is designed to work in conjunction with soffit vents, which control the incoming airflow, and the fan’s peak draw of 400 cfm per 1,000 square feet of attic area isn’t enough to create negative pressure in the attic.
Although the one-piece fan assembly and gasket are designed for retrofitting into an existing passive roof vent housing, the fan can be mounted behind a gable vent with the solar panel on the roof. It can also be installed into a new opening cut into the roof. Retail cost is $229.