Flex connector needed for gas connection to suspended make-up air unit?

[HVAC-Novice]

I have a project with a suspended make-up air unit. The gas connection is steel-piped. The manufacturer doesn't show flex connection, but they also cover curb-mounted etc.

A mechanic pointed out the unit will vibrate and may sway a bit and requested there to be a flex connection. Is this typical and should be done for all units? The previous unit didn't have flex connection, but that doesn't mean it isn't needed.

I also want to know what to detail and specify in the future.

our code is IFGC.

 

[BLee_PE]

I believe a flex pipe (like CSST) is only required in seismic zones, on moveable equipment (dryers, kitchen equipment, etc), and rotating combustion engines (power generators).

The fan inside of the AHU should be balanced so as to not to cause swaying. If it is swaying there is a larger issue. It should be suspended with vibration isolation. Gas and hydronic piping connections can all be hard piped to unions. I would ask your mechanic if he also thinks flexible connectors would be required on heating or chilled water coil connections. Just on google images and you will find plenty of installs without flex connections.