Conventional Wisdom informs us that hot attics can be cooled with fans. A fan at the upper part of the roof will pull hot air out making it easier to cool the house. Seems logical.
 |
| Temperature controlled fan installed at gable vent |
Building Science informs us that air is a fluid. As such it flows from areas of higher to lower pressure along the path of least resistance.
 |
| Fan and Vent don’t match |
A typical exhaust fan pulls 1000 cubic feet of air per minute. To work as designed there should be no openings in the immediate vicinity of the fan: otherwise air will be drawn from the closest source, the path of least resistance.
 |
| How much air gets out? |
Assuming the fan is installed correctly (not pictured) the negative pressure produced by fan exhaust will adversely affect cooling and indoor air quality.
 |
| Air drawn from the fan will be replaced through the vents |
Bottom line: mechanical attic exhaust fans are rarely installed correctly, and, even when they are, they are often detrimental to safety, efficiency and health.
 |
| Negative Pressure has no Positive Outcome |
And don’t forget the costs of installation and operation.
Sometimes saving money means not wasting it