The AC Infinity Backdraft Damper, 200 mm is a one-way valve that drops into a duct run. Airflow pushes the aluminium shutter open; when the fan stops, the shutter falls shut under its own weight and closes the duct. Air goes one way and nothing comes back.
It matters most on a fan that cycles. Any fan on a thermostat, humidistat, timer or lights-on schedule spends most of its day idle — and every idle hour, an undampened duct is simply an open hole between your space and somewhere else. Gravity-operated, so there is no power, no wiring and nothing that can fail.
What people use it for
Home ventilation
- Stopping wind driving damp air back down a subfloor exhaust
- Killing cold draughts back through a bathroom or laundry duct
- Keeping insects and outside smells out of an idle run
- Roof space, garage and workshop extraction that runs intermittently
Hydroponic ventilation
- Stopping odour escaping back out an idle intake duct
- Holding negative pressure in a sealed room between fan cycles
- Keeping pests out of a tent through the ducting when lights are off
- Any run behind a carbon filter where unfiltered air must not travel backwards
Getting it right
| Orientation | Fit it with the airflow arrow pointing the way the air travels, and hang it so the shutter can fall closed. Fitted backwards the fan holds it shut against itself and airflow collapses. |
| Position | As close to the outside termination as you can still reach, so the longest possible length of duct stays closed. |
| With a grille | Damper inside, grille vent on the outside face. The damper stops backflow, the grille stops weather and vermin. |
Full specifications
| Manufacturer | AC Infinity Inc. |
| Product / model | Backdraft Damper 8″ / AC-BDD8-B |
| UPC | 819137021327 |
| Duct opening size | 200 mm (8″) |
| Insert length | 180 mm |
| Body material | Steel |
| Shutter material | Aluminium |
| Finish | Black powder coat |
| Operation | Gravity-closing, no power required |
FAQ
Do I really need one?
If the fan runs flat out around the clock, it is optional. If it cycles — a humidistat under a house, a lights-on schedule in a tent, a timer in a bathroom — it is the difference between a duct that closes when the fan stops and a permanent opening. In a subfloor, backflow undoes the drying you just paid for; in a grow room, it lets unfiltered air and odour travel the wrong way.
Which way round does it fit?
With the airflow, shutter downstream of the fan. There is an arrow on the body. Fitted the wrong way the fan pushes the shutter closed instead of open — if airflow dies right after fitting one, that is why.
Will it reduce my airflow?
A little, as anything in a duct does. The shutter lies flat against the housing wall when open, so the loss is small — considerably smaller than what you lose to a duct that backfills every time the fan cycles off.
Is it noisy?
It closes with a light tap as the fan winds down. Chatter while the fan is running means the fan is too slow to hold it fully open — lift the speed slightly, or the duct is oversized for the airflow you are moving.
Does it help with odour control?
Indirectly, and usefully. It does not scrub odour — that is a carbon filter — but it stops smell travelling back out through a duct that is not currently being pulled on, which is a common way odour escapes a room that otherwise has filtration sorted.
What sizes do you stock?
100 mm, 150 mm and 200 mm. This is the 200 mm; the others are 100 mm and 150 mm. Match it to the duct.
Is this genuine AC Infinity stock with an Australian warranty?
Yes. Quick Bloom Lights is the official Australian importer and distributor for AC Infinity. Stock is held in Sydney, orders ship domestically, and the two-year warranty is handled here rather than through an overseas seller.