A: Yes it will open but it will not close You will need a very strong wind to close the damper it will not close on itself as the fabric is to rigid.
A: I see no reason that this would not allow ain in from the vacuum. I don't know your set up, but an out side breeze or wind will push through the vent into your crawl space, and it would also allow rodents through. I have 2 dryers connected to one exhaust vent. On each leg of the wye I installed these to keep the exhaust from back feeding into the dryer that was not being used.
A: I don't think it would have ever closed in the first place.
A: The damper is for exhaust ducts and blocks backdrafts. The damper is normally open to allow air flow out, but closes and seals when a backdraft occurs. Crawl spaces should be well ventilated with all vents open to allow air flow in and out. Regards, Mark - Battic Door Energy
A: Yes. I have 2 dryers going into the same vent and used this to keep from back feeding into the dryer that was not being used.
A: This was designed for use with a dryer vent exhaust system.
A: No as it may cause a fire
A: Premium Back Draft Damper is installed into ductwork to prevent unwanted outdoor drafts from entering into your bathroom fan, kitchen fan, clothes dryer, etc. Thank you for shopping at The Home Depot. Charlotte of the Home Depot Community.