by Scott Ranck
Ventilated attics are common in Florida. Generally, at the eaves is some kind of perforated vent, and then up near the ridge of the roof will be other vents to circulate the air in the attic. If some ventilation is good, many people seem to think more is better. So there are on the market motorized attic vents and even solar-powered attic vents. I will talk about these two products separately.
First, motorized attic fans often use more electricity than they save on your cooling costs. The attic is already ventilated and just pulling some additional air out doesn’t make that much difference. Solar attic fans have a much higher first cost and, again, don’t make a significant difference in the temperature of the attic. Payback on the investment will take a very long time. The major problem with powered attic vents no matter what powers them is that they create a negative pressure in the attic space. One law of building science is that high pressure always moves to low pressure to balance itself. When negative pressure is created in your attic by the powered vent sucking the air out, it will balance and often pull your air conditioned air out of the house through every penetration in your ceiling. Most building scientists agree—powered attic vents create more problems than they solve. Buyer beware!
Scott Ranck is the Conservation Program Coordinator & Energy Specialist for Florida Public Utilities. Feel free to e-mail any energy-related questions or comments to Scott at firstname.lastname@example.org.