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Square galvanised steel backdraft damper with aluminium blades, 27 3/4 in frame, no flange

Dayton

Dayton 3HHL7 Backdraft Damper 27 3/4 in Square

SKU CH-CMPZ-DAWJN

A 27.8 in square backdraft damper with a galvanised steel frame, aluminium spring panels and 4.9 sq ft free area, mounting horizontally or vertically for 2000 fpm airflow

  • TypeNo Flange, Horizontal or Vertical Mount
  • No-flange design fits vertical or horizontal duct runs
  • 27 3/4 in square frame matches 28 in rough opening
  • Galvanised-steel frame with 20 ga thickness resists corrosion
  • 9 sq ft free area allows high-volume airflow
  • Spring-loaded aluminium blades close automatically at 2000 fpm max velocity

Square Backdraft Damper for 28-Inch Ducts

The Dayton 3HHL7 is a square backdraft damper designed for 28-inch nominal duct diameters. It fits both horizontal and vertical mounting orientations without a flange. The single-panel aluminium assembly suits exhaust or intake systems that require automatic airflow control.

Sustained Airflow Performance

Rated for a maximum air velocity of 2000 fpm and a maximum pressure of 1 in wc, the damper maintains consistent opening force under continuous flow. The 4.9 sq ft free area minimises restriction during prolonged operation. Spring-loaded aluminium blades return reliably after each cycle.

Thermal and Acoustic Behaviour

The galvanised steel frame and aluminium panels resist corrosion in typical ventilation environments. No motor or powered actuator is present, so the unit adds no electrical draw or mechanical noise. Operation is passive, driven solely by airflow pressure.

Highlights

  • No-flange design fits vertical or horizontal duct runs
  • 27 3/4 in square frame matches 28 in rough opening
  • Galvanised-steel frame with 20 ga thickness resists corrosion
  • 9 sq ft free area allows high-volume airflow
  • Spring-loaded aluminium blades close automatically at 2000 fpm max velocity

Specifications

BrandDAYTON
TypeNo Flange, Horizontal or Vertical Mount

Questions about this item

How much airflow resistance does the 20-gauge galvanized-steel frame add when the damper runs continuously at 2000 fpm?

The 20-gauge frame is rated for a maximum pressure of 1 in wc at 2000 fpm, so resistance stays within that limit during all-day operation.

What duct opening must already exist for the 27 3/4-inch square damper to fit without modification?

A 28-inch square rough opening is required; the damper's overall dimensions are 27 3/4 by 27 3/4 inches with a 4 1/2-inch depth.

Will the aluminum spring blades seal against an older 28-inch square duct that has no flange?

Yes, the no-flange design mounts vertically or horizontally directly into a 28-inch square rough opening, and the spring-loaded blades close by gravity when the fan stops.

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