Duct from supply to return

Hey guys I was looking at the 90 day warranty video from Nathan. The furnace has this duct that goes from supply to the return. Why is that there?

Barometric bypass damper for zoned systems.

Thanks David. At least I have something to google now

It will have a barometric bypass damper which needs to be properly oriented and adjusted too.

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I’ve never seen it before. Thanks for the video