What is this?

[caryseidner]

I saw this today during an inspection and I can't figure out what it is for. The two rectangular ducts are the supply and return right after (or before) the FAU. I assume this rod connects to a damper inside the round duct and there is a weight or counterbalance on the rod.

What is it for? Why would you ever want or need to open this path? Why a weight/counterbalance?

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[Bill Kibbel]

It's a barometric damper in a bypass on a zoned system.

When zone dampers are closed, air pressure builds up in the ducts. A bypass relieves the pressure.

[caryseidner]

Ahh.... That makes sense Bill. There are 2 zones for this FAU. Thank you very much!