Air Vent Inc

This is question #5 from the “Five Most Frequently Asked Questions at Air Vent’s Ask the Expert Seminars.” Q: How would you rank the types of intake vents in terms of “Good, Better, Best”? A: Intake ventilation is an often overlooked element of attic ventilation. It’s important to always include proper intake for the overall attic ventilation system. Let’s look at the airflow performance differences of the most common intake vents.

The “Good” vents are vented soffit panels – generally made by siding manufacturers – and individual rectangular undereave vents.  Many homeowners like the look of vented soffit panels and thus they are popular for that reason. However, as a functioning intake vent the vented soffit panel must have adequate Net Free Area (the unobstructed area through which air can flow through the vent measured in square inches) to balance with the NFA of the exhaust vents. Otherwise the attic ventilation system will be out of balance, which could result in inefficient airflow and possible weather infiltration. The manufacturer of the vented soffit panel can report the NFA specification of its product.

Rectangular undereave vents generally come in three sizes: 16” x 4”/16” x 6”/16” x 8”. The larger the vent the more NFA is provided through the vent. As long as undereave vents are positioned frequently in the soffit/overhang (Air Vent recommends ever rafter bay or roughly every 2-4 feet apart) they are a good option for intake airflow. Unfortunately, the sporadic spacing of these vents does not lend itself to a truly continuous intake airflow system.

The “Better” vents are continuous soffit vents and vented drip edge. Both of these vents provide non-stop, continuous intake airflow – which is the goal of an intake vent. There are no dead spots or breaks in the airflow. Plus, their 9 square inches of NFA per linear foot perfectly balances with most ridge vents (exhaust vents) – making it easy for an installer to balance the overall attic ventilation system.

We have ranked as “Best” The Edge Vent because it provides all of the performance benefits of the “better” vents (continuous, non-stop airflow and they perfectly balance with most ridge vents in terms of NFA) PLUS they have the added benefit of being a roof-top installed vent. Many roofing contractors dislike hassling with working overhead in a soffit/overhang, which is what must be done when installing most intake vents. But The Edge Vent allows the roofer to stay rooftop where he or she is most comfortable. It blends the best performance with easy installation.

Our next posting we’ll examine another attic ventilation topic. You can also visit our FAQ section.

This is question #4 from the “Five Most Frequently Asked Questions at Air Vent’s Ask the Expert Seminars.” Q: How would you rank the types of exhaust vents in terms of “Good, Better, Best”? A: Although Air Vent makes just about every type of residential exhaust vent available on the market we do not rank them equally. There are performance and aesthetic/appearance differences.

The “Good” vents are wind turbines, gable louvers and roof louvers (also called can vents, box vents, mushroom vents and pot vents). These vents have airflow limitations by the nature of their product design and their placement on the roof. For example, wind turbines and roof louvers are spaced out evenly along the roof a few feet below the peak. That leaves voids or dead spots between the vents that do not receive proper airflow. And because it takes multiple vents to provide adequate ventilation that creates multiple protrusions through an otherwise good looking roof. As for gable louvers, since they are installed in the gable ends of the home/attic the airflow is limited to the immediate area of the vent openings – the gables. Gable louvers do not properly pull air from the middle section of an attic.

The “Better” vents are power fans. Whether it’s a roof-mount design or a gable-mount design, electric powered or solar powered, power fans move a lot more air than any of the “Good” vents. The downside is they have moving parts which in time could fail.

The “Best” vents are ridge vents. Because they are installed along the entire ridge or peak of the roof they provide a continuous, non-stop flow of air along the entire underside of the roof deck. As for appearance, their low-profile design makes ridge vents much less noticeable on the roof compared to other exhaust vents. Ridge vents offer the best combination of performance and appearance.

Next posting we’ll take a look at another frequently asked question from our Air Vent seminar. You can also visit our FAQ section.

This is question #3 from the “Five Most Frequently Asked Questions at Air Vent’s Ask the Expert Seminars.”  Q: Is it possible to have too much attic ventilation? A: Yes and No.

If we’re talking about intake ventilation in the soffit/undereave or at the roof’s edge, no, we cannot have too much intake ventilation. In fact, if the attic ventilation system is going to be out balance it’s better to have too much intake compared to exhaust because any excess intake ventilation becomes exhaust on the leeward side of the house. The same is not true, however, with exhaust. If the amount of exhaust ventilation exceeds the amount of intake it’s possible that the exhaust vents will pull the needed intake air from themselves thereby leading to potential weather infiltration and inefficient attic ventilation airflow.  It’s best to have a balanced system with 50% intake and 50% exhaust but if that is not possible it’s better to be out of balance with more intake than it is to be out of balance with more exhaust.

Next posting we’ll take a look at another frequently asked question from our Air Vent seminars. You can also visit our FAQ  section.

Here is question #2 from the “Five Most Frequently Asked Questions at Air Vent’s Ask the Expert Seminars.”

Q: Is it OK to mix or combine multiple types of intake vents on the same roof?

A: During the Q & A session of our seminar this question is a logical follow-up to the earlier topic we examined specific to “mixing exhaust vents” on the same roof.

While Air Vent does not recommend the practice of mixing exhaust vents it is acceptable – and sometimes necessary – to mix or combine multiple types of intake vents on the same roof above a common attic. And unlike the potential consequences associated with mixing exhaust vents, short-circuiting is not a concern when mixing intake vents because the intake vents will be in the same wind pressure zone generally (which is not the case, by the way, with multiple types of exhaust vents).

Let’s say a roofing contractor hired to install a new roof notices that the attic does not have enough intake ventilation using rectangular undereave vents in the overhang. The contractor could add more undereave vents to boost the intake ventilation or the contractor could install a roof-top intake vent – like The Edge Vent – to increase the overall amount of intake Net Free Area. Undereave vents in the overhang and The Edge Vent on the roof’s edge are still in the general same pressure zone and thus will not short-circuit.

Next posting we’ll examine another frequently asked question from our Air Vent seminars. You can also visit our FAQ section.

We’d like to thank the 2,200+ roofing professionals throughout the US and Canada who attended our annual Attic Ventilation: Ask the Expert seminars this past 1^st quarter. It was our 2^nd best seminar season in terms of attendance (2010 is #1). We’re taking the summer and fall to review your suggestions we collected on the Feedback Forms. Our 14^th year of Air Vent seminars will kick off in January 2012.  In the meantime here are the “Five Most Frequently Asked Questions at Air Vent’s Ask the Expert Seminars” starting with …

• Q: Is it OK to mix or combine multiple types of attic exhaust vents on the same roof?
• A: There are generally five types of exhaust vents: ridge vents, wind turbines, gable louvers, roof louvers, and power fans (roof-mount power fans and gable-mount power fans). Air Vent does not recommend mixing two different types of exhaust vents on the same roof above a common attic because it could result in short-circuiting the attic ventilation system. If short-circuiting occurs one of the two exhaust vents can act as an intake vent – resulting in possible weather infiltration and less than optimal attic ventilation for the entire underside of the roof deck.

Often this question is asked because the homeowner is unsatisfied with the performance of the existing attic ventilation system – let’s say for example, wind turbines – and thus thinks adding another type of exhaust vent – let’s say for example, gable louvers – will give a boost to the exhaust vents or improve the overall attic ventilation system’s efficiency. While this line of reasoning by the homeowner is understandable it is nonetheless mistaken.

Air follows the path of least resistance. It’s looking for the closest opening it can find. The closest opening on a roof that has mixed/combined exhaust vents becomes the distance between the two different types of exhaust vents. That interrupts – or short-circuits – the intended path of the air, which is supposed to be from low on the roof (intake vents) to high on the roof (exhaust vents).

There are ways to improve the performance of an attic ventilation system. Resorting to short-circuiting is not one of them. Next posting we’ll examine another frequently asked question from our Air Vent seminars. You can also visit our FAQ section.