Enlarge 6” to 8”

Frankdozer

Member
Aug 31, 2016
51
Maine
I need to increase the chimney opening from 6” round to 8” round. The chimney facing is typical 4” brick and the chimney liner is your typical clay tile liner. I was thinking to first encapsulate the wall and hearth with plastic so as I would be in a plastic bubble and run HVAC flex from the bubble to a window fan to the closest window to exhaust the dust. Amazon sells an 8” round dry drill masonry bit. Rather than chipping out the brick and possibly cracking surrounding brick and matching existing grout never happens.
I welcome comments. The stove I want to install is the Grandma Bear .
Thanks,
Frank
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,492
central pa
I need to increase the chimney opening from 6” round to 8” round. The chimney facing is typical 4” brick and the chimney liner is your typical clay tile liner. I was thinking to first encapsulate the wall and hearth with plastic so as I would be in a plastic bubble and run HVAC flex from the bubble to a window fan to the closest window to exhaust the dust. Amazon sells an 8” round dry drill masonry bit. Rather than chipping out the brick and possibly cracking surrounding brick and matching existing grout never happens.
I welcome comments. The stove I want to install is the Grandma Bear .
Thanks,
Frank
First thing first what type of wall is the pipe passing through? Is it solid masonry or is there framing behind the brick?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,492
central pa
No wood framing anywhere.
Then your plan could work but personally I would just cut through with an impact hammer. It is much easier and less mess. Does the chimney also have the required clearances to combustibles?
 

Frankdozer

Member
Aug 31, 2016
51
Maine
Stand alone chimney, no combustibles. I thought about using an impact hammer but I don’t want to crack the surrounding brick .
I also thought about removing the 8” round collar on top of the stove and welding in a 6” round collar. But where as it’s the Grandma Bear with double doors I’m thinking I’d get less draw thru the stove and possibly get smoke in the room every time I open it
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,492
central pa
Stand alone chimney, no combustibles. I thought about using an impact hammer but I don’t want to crack the surrounding brick .
I also thought about removing the 8” round collar on top of the stove and welding in a 6” round collar. But where as it’s the Grandma Bear with double doors I’m thinking I’d get less draw thru the stove and possibly get smoke in the room every time I open it
So the chimney doesn't pass through combustibles at the ceiling or roof? Some people have done fine reducing them to 6" but it doesn't meet code. I find they work best on 7" actually. How tall is your chimney?
 

John Galt

Member
Oct 22, 2019
43
W Montana
You'll probably have to make a jig of some sort for the center bit to drill through or the outside bit will just walk all over the wall. You could just get a diamond cutting blade and a 4" grinder for about $50 and cut 1" spokes from the 6" hole being careful at the faces to maintain a nice edge. Then you have a grinder to play with after the project.
 

Frankdozer

Member
Aug 31, 2016
51
Maine
Good idea about the jig and good idea about the grinder. I like the jig idea the best.
I’ll pre drill an 8” round hole in 3/4” plywood and anchor it to the wall centering it with the existing 6” round hole .
Also I’ll need a hostage to help hold the giant 3/4” power drill which will turn the 8” round dry drill bit.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,492
central pa
Good idea about the jig and good idea about the grinder. I like the jig idea the best.
I’ll pre drill an 8” round hole in 3/4” plywood and anchor it to the wall centering it with the existing 6” round hole .
Also I’ll need a hostage to help hold the giant 3/4” power drill which will turn the 8” round dry drill bit.
You are making it much more complicated than it needs to be. An impact hammer will do that easily I do it all the time. And your pipe is upside down