Gas HW tank vent has flapper door, OK or not?

Common sense tells me this is not proper. Should the door be removed?

Thanks in advance…Don

Got a pic?

Sorry, no pic…visulize a vent that you might see on an exhaust for a gas dryer…round, 4 inch diameter with a flapper door that can pivot at the top. Hope that helps. Don

What happens when it rusts shut?:shock:

It is made of aluminum.