Nominal clay flue sizes

[willkil]

I'm pretty new to chimney rehabilitation, but a quick study. I've measured the two square flues on my chimney and would like confirmation of their nominal sizes. Here's what I measured and what I think their nominal sizes are:

Interior Size	Exterior Size	Proposed Nominal Size
6⅞"	8½"	8"
10⅞"	12½"	12"

Have I proposed the correct nominal sizes?

 

[bholler]

You are correct

 

[double-d]

Some manufactures of different components will call then 9 x 13 or 8 x 12. These components are usually adjustable with bolts or will fit different flue sizes. Such as Rain Caps or Dampers.

 

[willkil]

Some manufactures of different components will call then 9 x 13 or 8 x 12. These components are usually adjustable with bolts or will fit different flue sizes. Such as Rain Caps or Dampers.

Are you saying that this 13"x13" top damper would fit my 12" flue? Makes sense as the specs on that page say this:

• Fits Flue Width/Diameter: 10"-13" | 15"-18" | 7"-10"
• Fits Flue Depth: 10"-13" | 15"-18" | 7"-10"

 

[bholler]

Are you saying that this 13"x13" top damper would fit my 12" flue? Makes sense as the specs on that page say this:

Yes it will fit fine.

 

[willkil]

Thanks for your help @bholler and @double-d!