Air Intake Backflow Preventer Necessary?

The Tank Air Intake Backflow Preventer Necessary?

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  • #20426

    I have a john woods envirosense power vent hwtr.
    The intake has a backflow preventer (red circle) that is making a heavy thumping sound (mechanical, could wake the dead) every time the heater turns on. I have isolated the issue by disconnecting the intake at the blue arrow (see photo).

    It only happens on initial firing but every time and violently slams that preventer open and shut a few times.

    Is it necessary or can I cut it out?

    Attached files


    On similar applications I have never seen this put on the intakes. Is this a local code requirment?


    No, the guy put it in because the manual “Strongly suggests a backflow preventer in cold climates” along with directions on how to install.

    Has anyone ever seen it?

    Larry Weingarten

    Hi: I live in a mild part of California, so have not run across this. You might wnat to post the question in The Wall at and see if some cool Easterners respond. 😎

    Yours, Larry


    Thank you very much. I posted there. Cheers 🙂

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