With the recent massive hail storm Phoenix experience two years ago, many homeowners in Glendale were able to claim new roofs and AC units and roofing companies started popping up from out of nowhere.  One thing roofing company’s love is attic ventilation and without an understanding of how a home performs as a system, this can be more harmful than helpful. 

Attic ventilation can seem to be a good thing, you cool down your attic in the summer and less heat will get into your home.  Many homeowners also get told more attic ventilation will extend the life of the roof and when roofing sales people start down that path combined with homeowner speculation, too much of a good thing becomes bad. 

See roofers gone wild at:

http://gerryraysroofing.com/blogger/ventilation-issues-in-your-attic-space/

http://www.radiantbarrierguru.com/attic-ventilation-basic-tips/

Source: http://www.dom.com/about/conservation/pdf/attic_ventilation.pdf 

There is no documentation that attic fans actually extend the life of roofs and no documentation that they even help cool an attic.  I have stood in from of many attic fans and solar attic fans while performing energy analysis and blowing insulation and I can’t feel a thing.  I also didn't feel any cooler in an attic with a huge power fan than an attic without.  Well enough of my experience, let’s look at the studies that have been done on this topic.

It has been proven that attic fans installed without air and duct sealing a home will pull your conditioned air up from the house and into the attic.  Yes that’s right, the average house an equivalent of a 1 sq ft window open all the time from leakage connections to the attic.  If you had an attic fan that moves a lot of air you might as well leave your door open while the AC is running. 

Where attic fans become harmful is when they start pulling carbon monoxide in from an attached garage and cause a gas water heater to backdraft or pilot lights to go out on gas appliances.  Air leaks and wasting energy is fine, that can be fixed but having family become sick because of CO poisoning is dangerous and people need to be aware of attic fan side effects.

Proof about attic fans and their lies:
http://www.dom.com/about/conservation/pdf/attic_ventilation.pdf

“Unplanned Impacts On Houses By Powered Attic Ventilators” http://www.advancedenergy.org/buildings/knowledge_library/ventilation/Attic%20Ventilation%20Case%20Studies.pdf

http://www.servicemagic.com/article.show.5-Myths-about-Attic-Ventilation.16547.html

The best way to slow the attic heat from getting inside is simply adding more insulation.  Yes the garage and the attic gets very hot in the summer, and heat transfer is driven by temperature differences… but it is also driven by pressures (your AC unit) and pathways (holes and leakage).  You can greatly slow down the transfer of heat into your home with properly installed insulation up to R-30, air sealing attic penetrations and properly sealing your ductwork with verification testing.  If you are purchasing a new roof, light colored shingles are a great way to reflect the sunlight and making sure your home complies with current codes for attic ventilation.  Usually your home already has enough ventilation especially if you have the bird hole venting with gable vents on both sides of your attic, you don’t need any more attic ventilation.  As always if you like this article like us on Facebook for more energy saving tips!