16/08/2023
Will an attic fan help me stay more comfortable?
I keep getting this question from our customers in recent months as we are hitting warmer weather.
The idea is compelling, if your attic is trapping heat due to intense sun, why not try to cool the space with a fan? In practice, though it just doesn't pan out reliably and here is why;
Air moves the path of least resistance, in this case when you create a negative pressure inside your attic the air doesn't just come from outside. Unless your attic is perfectly sealed, there are still many connections to the interior of the home.
By introducing a fan, we can actually pull cool air from inside the home into the attic, causing your a/c to work harder and defeat the purpose of the fan. In extreme cases where there is insufficient ventilation in the attic to supply air to the attic fan, this can be enough to impact air quality and efficiency of cooling further by drawing air and moisture into the home from the crawl space or other undesired areas.
The right solution is to seal the attic to isolate air movement from the home as best as possible, and then increase the insulation in the attic. Heat also moves the path of least resistance, and modern code levels of R-49 are usually quite sufficient to reduce the discomfort of having a sweltering attic. In the next code cycle, we are looking at R-60 in my region, and you would be very hard-pressed to see much of a difference in comfort by introducing an attic fan once your home is insulated to that level.
Mechanical ventilation can play an important role in mitigating moisture and air quality in homes, but this particular approach rarely improves comfort and can actually increase energy use.
