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  • Air Seal Tech

Attic ventilation is not black magic

A very few things are more misunderstood than attic ventilation. What we need to realize is that ventilation is about circulating air to keep it cool both summer and winter and to reduce moisture levels. A lot of homes in our area have unreasonably and unseasonably high levels of moisture in the attic.

Understanding whether your home has the proper setup of attic ventilation can help protect the large investment that your home is. An attic that is properly ventilated will perform as it should and will reduce of eliminate ice dams in the winter. Will also keep the attic and in turn your home much cooler in the summer as well as . It will also help eliminate condensation in the winter which leads to ceiling leaks and stains as well as excessive mold growth in the attic

Here are some of the facts and fiction you need to know about attic ventilation.


A properly ventilated attic will have about 10 air changes per hour

You can only have one type of roof vent or you may turn an exhaust vent into an intake vent and pull rain or snow in.

Ridge vents are often ineffective in our climate when it snows as they can be covered by 2 or 3 inches of snow. Box vents and turbine vents are significantly more effective when it snows as a box vent is much more difficult to cover and a turbine is virtually impossible to have covered and rendered inoperable with snow.


More attic ventilation is better. Ventilation needs to be installed and balanced properly in order to be effective and should be set up in an approx 50/50 split between intake and exhaust, and skewing a bit heavier 60/40 towards intake only if necessary

I have enough soffit venting. If you have individual soffit vents and they are more than 20 years old it is almost certain that they have lost most of there open area due to dust, pollen, bugs and cottonwood fuzz among other things that have clogged them up. These can be a relatively cheap and easy fix that can greatly improve the functioning of your attic ventilation.

3 must do's for attic ventilation

1. Install all exhaust ventilation at the same height within a common attic area.

It is very important to install all exhaust vents at the same height or level - installation of exhaust vents at more than one level on a roof allows the upper exhaust vents to pull air from lower exhaust vents instead of the intake vents. This can cause damaging weather infiltration to a home or structure.

Intake air must come from intake vents located near the lower part of the attic space to properly ventilate the total attic area and eliminate weather infiltration.

2. Install only one type of exhaust ventilation within a common attic area.

Exhaust vents pull air from the easiest intake source; therefore vent types cannot be mixed. The use of different types of exhaust vents could make one of the exhaust vents act as intake for the other. 

As previously stated in step one, intake air must come from intake vents located near the lower part of the attic space to properly ventilate the total attic area and eliminate weather infiltration.

3. Install a balanced system of intake and exhaust ventilation.

50% intake ventilation – Intake vents located near the lower part of the attic area are required to balance out a ventilation system.

50% exhaust ventilation – Use a Lomanco ventilation selector guide or the calculators at to determine the number of vents needed to properly ventilate an attic to the ventilation minimum property standards. 

The Lomanco website is a valuable resource if you need any information on attic ventilation

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