6" Double wall through 8" Class A

[Mech e]

I did a search for this question and did not really find an answer. My daughter and SIL are going to replace a very inefficient 70s Fireview stove with our 88' Osburn Regent 1500. The class A through the attic is 8" and we only need double wall 6" from the Osburn. Can we just run the 6" from the stove up through the 8" class A to the top of the chimney? The total height above the stove is only about 13' or so. We would then get a trim piece to cover the 8" class A at the ceiling.

 

[DAKSY]

The PROPER way is to INCREASE from 6" to 8" at the ceiling support box.

 

[Mech e]

Can do. Any concerns about decrease in draft going to an 8" pipe at the ceiling support box?

 

[bholler]

Can do. Any concerns about decrease in draft going to an 8" pipe at the ceiling support box?

Being that short I would expect problems

 

[DAKSY]

***Being that short I would expect problems ***

Me too. You will probably need to increase the 8" height.

 

[Mech e]

Okay. We will have to sort out who made the 8" that is installed now so we can extend it.

 

[webby3650]

Everyone says this will be an issue. I had the opposite outcome.
My last house had an existing 8” chimney and I added a 6” chimney in the main part of the house. Both were minimum height, about 13’. I have a woodstove habit, so I hooked multiple stoves to both flues. Often on the 6”, then moved to the 8” flue. They all drafted better on the 8” flue. In my experience, my stoves ran better on an 8” than the 6” on minimum height. I suspect this would have the opposite effect if the flue was tall, or on an exterior chimney.

 

[Mech e]

Everyone says this will be an issue. I had the opposite outcome.
My last house had an existing 8” chimney and I added a 6” chimney in the main part of the house. Both were minimum height, about 13’. I have a woodstove habit, so I hooked multiple stoves to both flues. Often on the 6”, then moved to the 8” flue. They all drafted better on the 8” flue. In my experience, my stoves ran better on an 8” than the 6” on minimum height. I suspect this would have the opposite effect if the flue was tall, or on an exterior chimney.

Easy to test. We will connect the 6" to the 8" and give it a go. The stove breathes easily so it may be fine.

 

[DAKSY]

The install manual says a minimum height of 12 feet of 6" chimney is required,
so you are probably good to go, but testing will verify that...

 

[Mech e]

The PROPER way is to INCREASE from 6" to 8" at the ceiling support box.

My SIL got the stove installed per your recommendation. It draws very well. A fresh coat of paint and it still works great after 32+ years. Thanks for the help!