KEES louvers are ventilation components designed to accommodate airflow while blocking rain, debris, and pests from entry. They are commonly installed on the sides of buildings to allow air to pass in for intake or out for exhaust.
KEES standard louvers (LO) and drainable blade louvers (DL) are sized using a simple algebraic equation. Combined with our sizing and performance charts, KEES reps can reliably and easily arrive at multiple correct options for louver width and height for a given airflow.
The Equation For Sizing Louvers
The simple algebraic equation used by KEES to size an intake or exhaust louver expresses the relationship between louver airflow, velocity, and free area:
Free Area (sq. ft) = Airflow (CFM) / Velocity (FPM)
When clients come to KEES looking to specify louvers, they know the desired airflow and the performance charts of the louvers given the maximum free area velocity. KEES reps identify the optimal velocity and free area, then use the following Extruded Louver Performance Chart to find options for width and height.
How To Size a KEES Intake Louver
Here’s an example of the process of sizing an intake louver.
In this hypothetical scenario, a potential customer has gotten in touch with a KEES rep about specifying model DL intake louvers at 3,100 CFM. As this request is for intake louvers, the KEES rep knows the maximum velocity is where water penetration equals zero, otherwise fast-moving air could bring rain into the louver.
By referencing the following Louver Intake Air Flow Pressure Drop & Water Penetration Graph, the rep notes the maximum velocity where water penetration equals zero for a DL intake louver is 900 FPM.
Using the client’s supplied CFM and this velocity, the equation to determine free area for this intake louver order is the following:
3,100 CFM / 900 FPM = 3.44 sq. ft.
The rep then reviews the Extruded Louver Performance Chart for width and height configurations that match or exceed 3.44 sq. ft. The free area cannot go under 3.44, as that would increase the velocity of the air and raise the water penetration value above zero.
For this hypothetical client, the rep would recommend the following options:
36”x36”
48”x28”
72”x20”
How To Size a KEES Exhaust Louver
The process for sizing an exhaust louver is slightly different from an intake louver. As exhaust louvers do not draw in air, the water penetration level is not a concern. Instead, the goal is to minimize the pressure drop to maximize the system’s energy efficiency.
The intake lines on the Louver Intake Air Flow Pressure Drop & Water Penetration Graph can be safely used for sizing louvers for exhaust applications, keeping in mind that the exhaust pressure drop will always be less than the intake pressure drop.
For this hypothetical scenario, the client wants to specify DL exhaust louvers at the same 3,100 CFM and with a maximum pressure drop of .10 in w.g. Referencing the graph, the maximum velocity value is 800 FPM.
The free area value for this example is as follows:
3,100 CFM / 800 FPM = 3.88 sq. ft.
The rep references that value against the Extruded Louver Performance Chart to arrive at the following options for exhaust louver width and height:
54”x28”
48”x32”
30”x48”
Why Is It Important To Correctly Size a Louver?
Correctly sizing a louver ensures it performs reliably at the intended specifications. An incorrectly sized louver will be less energy efficient, may underperform, and may take up valuable space on a building’s wall.
Too Small: A louver that is too small will increase the velocity and pressure drop above the desired values. An intake louver which is sized too small will let rain in; an exhaust louver which is sized too small will elevate the pressure drop value.
Too Big: A louver that is too big will be a waste of money, as the client pays for a product that is larger than their needs. Additionally, it will compete with other building components for valuable wall space.
KEES Sizes Louvers Correctly and Reliably For Any Installation
When it comes to sizing louvers, KEES has the process down to a science. We offer a wide range of width and height options to correctly size intake and exhaust louvers for any installation. Need a size not on our chart? Contact a KEES rep for a custom louver sized to your exact specifications.
