What makes a wind driven rain resistant louver? Here are three key traits to look for when choosing louvers for wind driven rain resistance. The Condenser is quick reads on important HVAC topics.
All louvers can deflect rainfall. Even straight blades can deflect water before it infiltrates the louver and can naturally drain it from the louver’s face. This level of protection is fine for light weather conditions with calm winds. For severe weather, you need a louver that can reject heavy rainfall when winds are strong. You need wind drain rain resistant louvers. Here are three key traits that every wind driven rain louver should have.
As excess rain collects on the louver’s blades, there is a chance that water from higher blades can be carried through the louver as it slides off. This chance increases as rain and high winds pick up. Drainable blades provide pathways for captured water to leave the louver.
Drain troughs along the face side of the blade will collect the water as it slides down the blades. From here, the troughs can funnel the water through channels in the jambs, which lead to the sill of the louver. These features help the louver reject excess water, which is important during heavy rainfall. Check out "Drainable Louvers for Rainy Days" for a more in-depth look at drainable features in louvers.
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A similar issue can occur when water collects at the louver’s sill. Sills will often have a sloped surface for water to naturally slide out of the louver. However, during heavy rainfall, water can begin to collect on the sill as it drains out of the louver. This water can spill back through the louver if it continues to collect at the sill. Even just a small amount of splash back can damage your ductwork.
Drain pans are louver sill accessories that sit under the louver’s sill and behind it. The pan will often have a backplate that blocks the space between the sill and the bottom blade. Once installed, the drain pan will act as a secondary sill for splash back. When the water splashes through the sill, the pan will collect the excess water and direct it under the louver, towards the face. The open face of the pan provides a quick exit point for captured water to leave the louver.
Drain pans are optional on most louvers, but they are a good addition when rejecting excess rainwater. For certain severe weather louvers, including hurricane louvers, the drain pan will be a standard feature of the louver.
Drainable features and sill accessories are important, but the most important trait is testing. A louver isn’t considered wind driven rain resistant unless it has been tested and rated for wind driven rain in accordance with AMCA 500-L. Learn more about wind driven rain testing with this Newsstand article.
To summarize, wind driven rain testing subjects a louver to simulated rainfall at a predetermined rate while a fan pushes air against the face of the louver. The louver must be able to pass the air through the louver while blocking the rain. Louvers receive an Effectiveness Class rating based on how much water they reject throughout the test. To maintain an A Class rating, the louver must reject over 99% of incoming water.
Check the submittals for details. Manufacturers will post the results of the louver’s testing on the submittal, along with an AMCA CRP Ratings Seal.
For more on louvers, check out these Newsstand articles:
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