Made in the USA NOMMA
36 West Pennsylvania Avenue Walkersville, MD 21793

Custom Fabricated Louvers by Hercules Custom Iron, LLC.

How Custom Louver Sizing and Installation Work with HVAC Units

How Custom Louver Sizing and Installation Work with HVAC Units

Louvers do an excellent job at covering up the exterior wall opening required for the exhaust of an HVAC system.

If you’re considering hiring licensed professionals to install custom louvers on your property, you might have a few questions about them. For custom louvers, form and function typically go hand in hand. For louvers, it’s a relatively attractive way to cover up the exterior wall opening required for the murky air intake and exhaust of an HVAC system. Custom louvers also do an excellent job providing privacy and keep water, wind, and intruders out of your property. Here are a few pointers on how contractors decide precisely how to size and install custom louver for your property’s HVAC system.

The Cut for Your Custom Louvers

The entire process of determining proper custom louver sizing should precede the cut into the outside wall. If the louver doesn’t align perfectly with the back of the HVAC system, a rear extension can be used to assist in fitting the unit. The hole should be sized to ensure a close enough fit to prevent any water from intruding.

Open Area

The open, or free area, is defined as space through which both fresh and discharged air will flow throughout the custom louver. It is the space that isn’t occupied by any louver blades. This will account for about 35 to 60 percent of the total louver space. A supplier will generally provide a chart specifying the amount of free space needed to provide fresh air to the specified unit.

Intake vs. Exhaust Split 

The split wall sleeve behind the custom louver separates fresh air from any exhaust air. The splits are then set at a slight angle to shed off moisture and are based on the preferred percentage of intake to exhaust. For example, 55 (intake percent to 45 (exhaust) percent. The required split is determined by the needs of individual units and can be determined using calculated formulas. 

Free Area Velocity

This is just the flow rate of air divided by the cross-sectional area that it moves through.

Rated Water Penetration Velocity

This is the intake speed at which your HVAC unit will begin to draw water through the custom louver. This is a vital value because it sets the threshold at which a custom louver can allow any damaging water into your property and your HVAC system. This value is normally provided in the catalog that is accompanied by your custom louver.

There’s plenty of variables to consider when installing custom louvers, and sometimes it can be tricky. Feel free to call Hercules Custom Louvers for all your louver installation needs!


When you are ready for quality louvers, the professionals at Hercules Custom Louvers are ready to help. For more information and to learn how we can meet your custom louver needs, contact Hercules Custom Louvers online or giving us a call at 1-800-331-2590. We will ensure your investment serves your property for years to come! For updates and to see projects we’re working on, visit us on FacebookTwitterTwitterYouTube, and Pinterest.

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Hercules Louvers
36 West Pennsylvania Avenue Walkersville, MD 21793
Phone: 1.800.331.2590