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Attic Ventilation: You Don’t Need Attic Fans

As unglamorous and out of sight as it may be, your attic could be making or breaking your home’s comfort and energy bills.

In a traditional attic, the ventilation system consists of openings along the eaves, ridges, tops of gables, or piped vents protruding from the roof. This is a passive system that requires vents and openings to be properly sized, oriented, and clear of obstructions. In summer, the air movement is meant to absorb heat that has accumulated to building materials in the attic when the sun pounds on your roof. The cool air enters at the sides and bottom of the attic (gables or eaves), pulls heat from the surface and exits the top (gables). When it is very cold outside, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent out any moisture that moves from the conditioned living space to the attic.

Attic ventilation
Attic ventilation

While we are advocates for passive venting, ecobeco is not a fan of attic fans! In the most common attic fan use case, people with really hot attics are using electric fans to cool the attic. But instead of pulling in air from the gables or eaves, the attic fans are pulling in air from the poorly sealed attic floor that is directly connected to the upper level of the house. In other words, the fan pulls air conditioning into the attic. That’s just wrong! When you properly air seal and insulate an attic, you don’t need to spend money running an attic fan. Instead, the attic floor acts as an air barrier that keeps your air conditioning in the house longer. The insulation acts as a barrier that prevents the warm sun from penetrating the attic floor and entering your home. In the winter time, insulation prevents heat from moving from your living space to your attic, and the sealed attic floor keep the heat in the house longer.

There are certain types of roof configurations where, due to poor design, the passive ventilation strategy may not work for your needs.  A hip roof (think of a Pizza Hut restaurant building) is an example where there may be too much heat and moisture building up, and perhaps you store stuff in your attic and want to control the attic temperature.  In this case, you might use an attic fan to ensure that the attic does not get too hot.  But to save money and keep your home comfortable, make sure that you isolate the attic from the living space.  Home Performance contractors such as ecobeco can help.  And if you really need to control the temperature in your attic because, let’s say, you want your mother-in-law to live in the attic, then go ahead and enclose the attic space and bring it into the conditioned part of the house.

Sources and for more information:

http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

https://www.energystar.gov/index.cfm?c=diy.diy_attic_ventilation

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