Dampers and Louvers Information

Tornado damper from GreenheckDampers and louvers control the flow of air in a process system or enclosed area. Dampers are usually motorized or manually-adjustable for flow control. They can modulate gas or air flow, detour flow into alternative systems, or isolate a process for inspection and repair.

Louvers are a type of damper consisting of several blades mounted parallel across a duct. They are versatile and are a lightweight, compact, and have a low leakage to the outside environment. Their disadvantages include a flimsiness of long thin blades tends to promote flutter, sealing problems in dirty applications, and a higher pressure drop due to the obstruction of flow by the blades. Louvers are often fixed for a constant flow rate.


Types of Dampers and Louvers

Dampers are made of metal and usually square, circular, or rectangular in shape. Some industrial dampers are designed for pressure relief, or recommended for use within specific HVAC systems.

Like dampers, louvers are usually made of aluminum or steel. Louvers may be adjustable, or suitable for applications that require noise control.

Damper Types

Dampers are designated as industrial control, backdraft, counterbalanced, bubble tight, isolation, or discharge products.

  • Fire damper from FlaktwoodsBackdraft dampers have a galvanized steel frame and extruded aluminum airfoil blades. These vanes provide improved strength with reduced noise and static pressure.
  • Counterbalanced backdraft dampers are usually made of galvanized steel. They are designed to meet application requirements based on temperature, pressure, or velocity.
  • Industrial dampers include bubble tight dampers, round isolation dampers, and round discharge dampers.
    • Bubble tight dampers are used in applications that require shut-off capabilities under extreme conditions. They may be qualified for use in nuclear power plants and tested according to ASTM and ASME standards.
    • Round isolation dampers are made of carbon steel and have a butterfly blade. They provide extremely low leakage in both HVAC and process systems.
    • Round discharge dampers are also made of galvanized steel, but are designed for use on the discharge side of an axial flow fan. These dampers prevent fan shutdown and can withstand pressures and velocities in multi-fan applications.

Louver Types

There are four basic types of industrial louvers: stationary, adjustable, combination, and air measuring.

  • Stationary louvers are equipped with angled or airfoil-style blades that may provide weather protection and sound attenuation.
  • Adjustable louvers with airfoil blades are also commonly available.
  • Combination louvers have blades that begin to open at one level of static pressure and become fully open at another. They may have backdraft damper blades and feature an all-aluminum construction for corrosion resistance.
  • Air measuring louvers have closely-spaced vertical blades that prevent ingress of water.


Important specifications of the system to consider when selecting a damper include temperature, pressure, gas chemistry, flow velocity and pressure loss, and particulates. 

Additional considerations include the environment in which the damper will preform. Some dampers are better designed for outside environments where rain, cold, and heat can affect the blades of the damper causing blockages, warping, and failure. 


Damper Dan's Website


AMCA 500 -- Test methods for louvers, dampers, and shuttles

ASHRAE 90138 -- Information on dampers and airflow control

Images Credits:

Greenheck | FläktWoods

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Texel-Seikow USA, Inc.
Texel-Seikow USA, Inc.


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