Is an 8" liner generally ok for 6" stoves?

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53flyer

New Member
Oct 21, 2009
175
Eastern WA
I understand that "some" 8" stoves can go into 6" liners but not always but what about the opposite way? I.e. will most 6" stoves be ok hooked up to an 8" liner? Given the option between "only" those 2 hookups which would you take as the least problematic?
 

snowtime

Minister of Fire
Oct 31, 2007
523
northern BC
I would fix the situation not just make due. If I had a 6" pipe and a stove that took 8" I would either replace the stove or pipe same with the 8".
 
T

theheatelement

Guest
It's more about how your stove was tested in regards to if it should work... Other then that its just tried and true testominals. But every situation is different so if 1 person said it worked on their situation it is not a guarantee that it will work on yours.
 

LLigetfa

Minister of Fire
Nov 9, 2008
7,360
NW Ontario
It depends on how tall the flue and how warm it is. Gasses move much slower in a larger flue and have more time to cool off and lose the buoyancy. The less heat and volume the stove allows up the flue, the worse the draft can get. Insulated liner would be better than uninsulated. Central masonry would be better than exterior.
 

grommal

Feeling the Heat
Mar 4, 2009
487
Eastern PA
LLigetfa said:
It depends on how tall the flue and how warm it is. Gasses move much slower in a larger flue and have more time to cool off and lose the buoyancy. The less heat and volume the stove allows up the flue, the worse the draft can get. Insulated liner would be better than uninsulated. Central masonry would be better than exterior.
Absolutely true. But the only way to tell if it will work is to try it out. Many stove manufacturers with 6" outlets say a larger flue is ok as long as it's not more than 2X the area. An 8" round has about 1.8x the area of 6".

I was very concerned with my installation, as I kind of have the worst case. I have a relatively short, exterior, masonry chimney, with 8" clay liner. But, my Oslo seems very happy with it. I do sometimes have to start the draft if the weather isn't very cold, but once it's going the right way, it's happy. You never know until you tive it a try.
 

Battenkiller

Minister of Fire
Nov 26, 2009
3,739
Just Outside the Blue Line
grommal said:
I have a relatively short, exterior, masonry chimney, with 8" clay liner. But, my Oslo seems very happy with it. I do sometimes have to start the draft if the weather isn't very cold, but once it's going the right way, it's happy.
Maybe this should be a separate question, but it ties in here.

I have an interior masonry chimney with a 7" clay liner. My local stove shop said it would be insufficient for my new Vermont Castings Vigilant, which requires a minimum of an 8" flue pipe. I don't get it since an 8" pipe has about 50 sq.in. of area while a 7" square liner has a 49 sq.in. area.

Does the square shape as opposed to a round pipe affect the draw?

Anyway, it seems to be working fine at this point. From what I've always understood, narrow flues increase velocity but obviously limit the amount of air that can travel up the flue. In my case, I have a very tall chimney (extends from the basement through two stories and then another 4' above the roof peak. I think the added velocity helps to move those gases up and out before they condense. I used to burn a lot of unseasoned wood in my old stove, mostly ash and cherry. I always got very little creosote because I followed my sweep's advice and ran the stove full blast for an hour every morning to get the chimney hot. He no longer yells at me about the creosote.

BTW, grommel, what do you mean by "start the draft"?
 
T

theheatelement

Guest
6" liner has a sq area of 28.27433
7" liner has a sq area of 38.48451
8" liner has a sq area of 50.26548

Battenkiller said:
grommal said:
I have a relatively short, exterior, masonry chimney, with 8" clay liner. But, my Oslo seems very happy with it. I do sometimes have to start the draft if the weather isn't very cold, but once it's going the right way, it's happy.
Maybe this should be a separate question, but it ties in here.

I have an interior masonry chimney with a 7" clay liner. My local stove shop said it would be insufficient for my new Vermont Castings Vigilant, which requires a minimum of an 8" flue pipe. I don't get it since an 8" pipe has about 50 sq.in. of area while a 7" square liner has a 49 sq.in. area.

Does the square shape as opposed to a round pipe affect the draw?

Anyway, it seems to be working fine at this point. From what I've always understood, narrow flues increase velocity but obviously limit the amount of air that can travel up the flue. In my case, I have a very tall chimney (extends from the basement through two stories and then another 4' above the roof peak. I think the added velocity helps to move those gases up and out before they condense. I used to burn a lot of unseasoned wood in my old stove, mostly ash and cherry. I always got very little creosote because I followed my sweep's advice and ran the stove full blast for an hour every morning to get the chimney hot. He no longer yells at me about the creosote.

BTW, grommel, what do you mean by "start the draft"?
 

Battenkiller

Minister of Fire
Nov 26, 2009
3,739
Just Outside the Blue Line
TheHeatElement said:
6" liner has a sq area of 28.27433
7" liner has a sq area of 38.48451
8" liner has a sq area of 50.26548
My clay tile liner is 7" x 7" square inside dimension (I actually measured it with a steel tape and it is about 7 1/4"). 7" x 7" = 49 sq.in. The figures you give are for round liner (pi x radius squared).

That said, the 8" flue pipe is reduced to 7" round at the nipple, so there is a very short run of about 6" in length where the area is reduced (depth of the nipple itself) before it goes back to 7" x 7" square. Will that really make any difference?
 

grommal

Feeling the Heat
Mar 4, 2009
487
Eastern PA
TheHeatElement said:
6" liner has a sq area of 28.27433
7" liner has a sq area of 38.48451
8" liner has a sq area of 50.26548

Battenkiller said:
grommal said:
I have a relatively short, exterior, masonry chimney, with 8" clay liner. But, my Oslo seems very happy with it. I do sometimes have to start the draft if the weather isn't very cold, but once it's going the right way, it's happy.
Maybe this should be a separate question, but it ties in here.

I have an interior masonry chimney with a 7" clay liner. My local stove shop said it would be insufficient for my new Vermont Castings Vigilant, which requires a minimum of an 8" flue pipe. I don't get it since an 8" pipe has about 50 sq.in. of area while a 7" square liner has a 49 sq.in. area.

Does the square shape as opposed to a round pipe affect the draw?

Anyway, it seems to be working fine at this point. From what I've always understood, narrow flues increase velocity but obviously limit the amount of air that can travel up the flue. In my case, I have a very tall chimney (extends from the basement through two stories and then another 4' above the roof peak. I think the added velocity helps to move those gases up and out before they condense. I used to burn a lot of unseasoned wood in my old stove, mostly ash and cherry. I always got very little creosote because I followed my sweep's advice and ran the stove full blast for an hour every morning to get the chimney hot. He no longer yells at me about the creosote.

BTW, grommel, what do you mean by "start the draft"?
What I mean is that the combination of my chimney height (or lack thereof), roof line, nearby trees, and whatever else, sometimes has my chimney downdrafting when I go to start the stove, especially if the weather is not super-cold. Like others with the problem, I need to take steps to heat the air in the flue, or open a window on the high pressure side of the house, or both, to get it to turn around. Once turned, it's fine.
 

summit

Minister of Fire
Aug 22, 2008
1,900
central maine
I'd plug a 6" outlet into an 8" flue all day, and not lose a minute of sleep over it....
 
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