Make sure your whole house fan is insulated and air tight so it doesn’t look like this!There are a number of companies promoting and selling large fans that install in the ceiling of a central location (typically) that pull in air from the outside and force that air into the attic and out the attic vents.While doing home energy ratings I’d often get asked if a whole house fan is a good solution to reduce energy bills.  The idea is that when it gets cooler outdoors than it is indoors then the whole house fan is used to draw in that cooler air instead of using air conditioning in the home.

There are whole house fans out there that are insulated and (almost) air tight.  Those whole house fans provide you with the comfort during the summer time while insulating your home from the attic when that whole house fan isn’t running.  So when you’re shopping for a whole house fan make sure that it’s insulated and will be air tight when its not running.  These systems can also include a thermostat to help manage how long the fan runs in the evening.

I know several people who own whole house fans and they are the older style, metal surface whole house fans with louvers that open and close with the change of air movement.  They are not air tight and they do not have insulation.  Those fans are good while they are running, but the other 95% of the time when they are off or during winter time they are essentially a hole into the attic, which can defeat the purpose of all of your attic insulation. In fact that whole house fan will look like a BBQ during the summertime with the use of a thermal camera as pictured above.

Check out this technical bulletin from PG&E on whole house fans.