3 questions about ceiling support boxes and attic radiation shields

[Charles2]

1. Which is better, round or square support boxes?

2. How much wider than stovepipe are support boxes?

3. For floor and roof trusses spaced 24" OC, are some manufacturers' ceiling support boxes and attic radiation shields easier to install than others, or are they all about the same? What about installation of the attic radiation shield near an eave where there is no headroom to work in the attic?

 

[bholler]

I think you need a pro to install it lol.

All of these questions will be answered when you read the instructions for your chimney