Flex heating duct clearance

What is the recommended clearance of flex duct to sigle wall chimney? Same a clearance to wood? Thanks

Don’t think I understand the question in my area single wall pipe is not allowed above the drywall ceiling

I’ve got a single wall chimney pipe comming of a water heater. There is a flexible heat duct running over the single wall pipe. I was going to report there should be 6" clearance, but thought it may need to be more clearance since the flex duct has a plastic covering.

Ok I got the Pic and yes there has to be at least 6 inches clearance on single wall to anything combustible.

Thank you!