What is the difference between the BDD and the BDH Back Draft Hood?

The BDD is an inline duct product — it installs inside the duct run between duct sections at any point where reverse airflow needs to be stopped. The BDH is a wall termination hood — it installs at the building exterior where the exhaust duct exits through the wall. On a fresh air intake run, you would use the OOH or BDH at the wall and install a BDD in the duct run downstream of the motorized HAC damper if a secondary seal is required.

Can I use the BDD in any mounting orientation?

Yes — any orientation. The spring closes the blade regardless of whether the damper is mounted horizontally, vertically, inverted, or at an angle. This is the primary advantage of the spring-return design over gravity-close alternatives. Gravity dampers require near-horizontal mounting to close correctly. The BDD does not.

What is the butterfly style and when should I use it?

The butterfly style (-B suffix) insets into an existing duct opening without a full body — suited for retrofit applications where adding a full inline section is impractical. It is available in 4 inch through 6 inch only. For retrofit applications above 6 inch, install a short inline section and use the standard BDD. For new installations, use the standard inline style — it is more reliable and available in the full size range up to 24 inch.

Should I use a BDD with a motorized HAC damper on a fresh air run?

It depends on the application. A motorized HAC provides powered open/close control and closes reliably on command. A BDD downstream provides a passive secondary seal that closes immediately on any reverse airflow event — including during the brief period between fan shutdown and HAC closure, and on power loss events where the HAC may be mid-travel. On HRV and ERV fresh air runs in cold climates, the BDD is commonly specified as a secondary seal.

Is there an end switch option on the BDD?

No. The BDD is a passive mechanical product — no electrical components, no wiring, no end switch. If position confirmation is required in the duct run, the PFS Positive Flow Switch confirms actual airflow. For motorized open/close control with position confirmation, use a motorized HAC damper with the end switch option.

BDD Back Draft Damper for HVAC Ducts, Spring Return

Spring-return back draft damper for inline duct applications. Allows airflow in the forward direction and closes against reverse airflow: no power, no wiring, no control sequence. Spring closes the blade in any mounting orientation: horizontal, vertical, inverted, or any angle. Standard inline 4"–24". Inset butterfly (-B suffix) for retrofit into existing duct openings, 4"–6".

✓ Spring return: any mounting orientation. Closes regardless of whether the duct is horizontal, vertical, or angled; gravity-close alternatives require near-horizontal mounting to work correctly

✓ No power, no wiring, nothing to fail electrically: passive mechanical operation; spring mechanism and galvanized steel body with a 10-year mechanical warranty

✓ Secondary seal on HAC fresh air runs: standard practice on HRV/ERV fresh air duct runs in cold climates; BDD downstream of the motorized HAC provides passive protection on power loss and during HAC blade travel

✓ Butterfly style (-B) for retrofit: insets into existing duct opening without a full inline body; 4"–6" only; for retrofit above 6" install a short inline section with the standard BDD

✓ Confirm airflow direction before installing: BDD is not bidirectional; an arrow on the body indicates the correct forward flow direction; reverse installation means the spring holds the blade closed against normal airflow

Not for at-wall termination applications. The BDD is an inline duct product. It installs inside the duct run between duct sections. For a back draft damper at the building exterior wall use the BDH Back Draft Hood. For adjustable bypass pressure relief on zone systems use the HAC-BPD.

Standard Inline: use for…

✓New installations: full duct fitting, installs inline like any round section

✓Full size range 4"–24": the correct choice for 7" and above

✓Any application where the duct run is being modified or replaced

✓More reliable installation: full body, standard duct connections

Butterfly (-B): use for…

→Retrofit into existing duct opening, no full inline body required

→4"–6" only: tight spaces where adding a full inline section is impractical

→Existing duct opening is already correct size: butterfly relies on close fit to seal

→For retrofit above 6": use a short inline section + standard BDD instead

Example	Part Number	Style
4" inline	BDD-0400-000	Standard inline
6" inline	BDD-0600-000	Standard inline
6" butterfly	BDD-0600-000-B	Inset butterfly: retrofit
8" inline	BDD-0800-000	Standard inline
12" inline	BDD-1200-000	Standard inline
24" inline	BDD-2400-000	Standard inline: largest standard size

Part number structure: BDD-[size as 4 digits]-000 for inline; add -B suffix for butterfly. Sizes above 24" contact factory.

Mounting

Any orientation: spring closes

Inline Sizes

4"–24" standard

Butterfly Sizes

4"–6" only

Operation

No power, no wiring

Construction

Galvanized steel

Warranty

10-year mechanical

Need position confirmation or actual airflow measurement? The BDD is passive: no end switch, no electrical output. For confirmed blade position on a motorized damper use the HAC with end switch option. For actual airflow confirmation in the duct run use the PFS Positive Flow Switch. For a back draft damper at the building wall exterior use the BDH Back Draft Hood.

10-year mechanical warranty

Made in Canada · No power, no wiring, nothing to fail electrically

Product image is representative only. Actual product may differ in appearance depending on size, configuration, and options selected at order.

BDD Back Draft Damper, Spring Return, Any Orientation, Inline or Butterfly, 4"–24"

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BDD Back Draft Damper, Spring Return, Any Orientation, Inline or Butterfly, 4"–24"

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