Stupid Fan Tricks

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


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