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Square stainless steel backdraft damper with two panels 33 by 33 inches

Dayton

Dayton 4FZJ9 Backdraft Damper 30 in 33 in 5.4 sq ft 2500 fpm

SKU CH-J2AQ-JB27V MPN 4FZJ9

Stainless-steel backdraft damper with two panels, 5.4 sq ft free area and 2500 fpm maximum air velocity

  • TypeDrain Components
  • 30-inch fan fit for direct duct compatibility
  • 33-inch square frame matches standard rough openings
  • 4 sq ft free area allows high-volume airflow
  • 2500 fpm maximum velocity handles demanding exhaust systems
  • Stainless steel construction resists corrosion in harsh environments

Purpose and audience

The Dayton 4FZJ9 is a stainless steel backdraft damper designed for 30 inch fan installations. It prevents reverse airflow in duct systems where gravity or pressure differentials could otherwise push air the wrong way. Contractors and facility managers specify it for commercial and industrial exhaust or supply applications that demand corrosion-resistant construction.

Decisive specification

The damper provides a free area of 5.4 square feet and is rated for a maximum air velocity of 2500 feet per minute. These two figures together determine whether the unit can handle the required airflow without excessive pressure drop or noise. If the system design calls for a larger free area or higher velocity rating, this model will not meet the specification.

Installation context

The unit fits a square rough opening of 30 1/2 inches by 30 1/2 inches and has an overall height and width of 33 inches with a 5 1/4 inch length and 2 inch frame depth. Its two-panel stainless steel frame mounts directly into the opening without additional duct connections. The damper frees up design flexibility by eliminating the need for motorised actuators in gravity-relief applications.

Highlights

  • 30-inch fan fit for direct duct compatibility
  • 33-inch square frame matches standard rough openings
  • 4 sq ft free area allows high-volume airflow
  • 2500 fpm maximum velocity handles demanding exhaust systems
  • Stainless steel construction resists corrosion in harsh environments

Specifications

TypeDrain Components
BrandDayton
Model4FZJ9

Questions about this item

What does the 2500 fpm rating tell me about airflow in a real installation?

The 2500 fpm rating is the maximum air velocity the damper can handle without excessive pressure drop or blade flutter, so size the duct and fan to stay at or below this speed for quiet, efficient operation.

How does the square rough opening interface with standard ductwork?

The damper fits a 30-1/2 in square rough opening and uses a 2 in deep stainless-steel frame that bolts or screws to the duct flange, providing a rigid, airtight connection for backdraft prevention.

What are the exact outside dimensions I need to clear for mounting?

The unit measures 33 in high by 33 in wide with an overall depth of 5-1/4 in, so allow at least that footprint plus fastener clearance when planning the wall or roof penetration.

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