Attic Fans
Monday, July 25, 2011: Updated Monday January 6, 2014
A couple of years ago, I installed a thermostat controlled attic fan.
I had read that venting out the heat in the attic will reduce cooling costs, (makes sense). But it also takes energy to spin a large fan for 10 hours every day.
If the house isn't properly air sealed, cool conditioned air from the house will be sucked into the attic space and vented outside. In this case, the central air conditioner will use more energy with an attic fan running.
If the attic is far under ventilated, the attic fan will not be able to draw out enough hot air to make a difference but still draw a lot of power.
If the attic has superior ventilation (most homes, including mine don't), an attic fan will not do any good either because the attic vents are already doing the an attic fan's job only passively.
Ever since I air-sealed our home, I have been wanting to quantify the attic fan's performance and usefulness. I got the chance this weekend when my entire family was away and left me home alone. No stoves cooking, no kids leaving outside doors open, no TV's being left on. Just a relatively constant, measurable whole house power consumption. To help in comparing apples to apples, the weather forecast all weekend was sunny and in the low 90's .
I ran one day with the attic fan on and one day with it off.
