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 – Spring Return, Any Orientation, 4

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

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

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

Description

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