Which size would draw better for my chimney?

[jaydee]

Just a quick question:

I have a 15 foot high chimney. I can easily use either a 6 or 8 inch liner.
I'm vacilating between two stove models, one that would take a 6 inch liner and the other an 8 inch.

With a fairly short chimney, would either size make a difference in the ability to draw properly?

With either one, the liner will be insulated and extend the full length.

 

[begreen]

The majority of stoves have 6" pipe, so a 6" flue will accommodate more stoves. If there is an 8" flue and later on you switch to a 6" flue stove, it may not draft as well, especially if there are elbows involved in the connection.

 

[EatenByLimestone]

I agree completely. There doesn't sound like a huge difference is pipe size there, but a 6" pipe has an area of 28.26sq in. and an 8" pipe has an area of 50.24sq in. That's a good amount more air that would have to be heated in order to give a good draft.

Matt

 

[jaydee]

thanks, guys. I'm not that great with physics, but that was my gut feeling. Appreciate it!

 

[Fsappo]

Use 8" for the 8" stove and 6" for the 6" stove. You can use the 6" stove with an 8" chimney, but it's always good practice to run the same volume of air from the stove outlet to the chimney cap.

 

[vvvv]

I agree completely. There doesn't sound like a huge difference is pipe size there, but a 6" pipe has an area of 28.26sq in. and an 8" pipe has an area of 50.24sq in. That's a good amount more air that would have to be heated in order to give a good draft.

Matt

logic 4 analysis= 6" stove exhaust allows for a 6 or 8" chimney. An 8" stove exhaust disallows a 6" chimney? I'd guess the 8" has better draft.

 

[Fsappo]

I agree completely. There doesn't sound like a huge difference is pipe size there, but a 6" pipe has an area of 28.26sq in. and an 8" pipe has an area of 50.24sq in. That's a good amount more air that would have to be heated in order to give a good draft.

Matt

logic 4 analysis= 6" stove exhaust allows for a 6 or 8" chimney. An 8" stove exhaust disallows a 6" chimney? I'd guess the 8" has better draft.

To a certain extent, but you can reach a point of diminishing returns and beyond that a reversal of performance by increasing the chimney size

 

[vvvv]

I agree completely. There doesn't sound like a huge difference is pipe size there, but a 6" pipe has an area of 28.26sq in. and an 8" pipe has an area of 50.24sq in. That's a good amount more air that would have to be heated in order to give a good draft.

Matt

logic 4 analysis= 6" stove exhaust allows for a 6 or 8" chimney. An 8" stove exhaust disallows a 6" chimney? I'd guess the 8" has better draft.

To a certain extent, but you can reach a point of diminishing returns and beyond that a reversal of performance by increasing the chimney size

reversal of performance from too much draft?

 

[Fsappo]

Someone else will be able to answer this better than I, but as a chimney gets larger than a stove is designed to use..at some point..the stove will have to work harder to create and maintain proper draft during the full curve of a typical wood fire. So, a 6" stove into an 8" chimney in almost every case would work fine..almost every case.

 

[oldspark]

There is a variance from the stove flue size and I believe it is 20 or 25 percent, I assume that is down or up is size as some people on here have had to use a 5 inch liner and they said it worked fine. I have a 7 and 1/4 inch liner and it works fine for my 6 inch flue on my summit, my old stove (non EPA) was an 8 inch and it worked fine for that.

 

[vvvv]

Someone else will be able to answer this better than I, but as a chimney gets larger than a stove is designed to use..at some point..the stove will have to work harder to create and maintain proper draft during the full curve of a typical wood fire. So, a 6" stove into an 8" chimney in almost every case would work fine..almost every case.

u sell the stoves & got the manuals so do any say not to oversize the chimney?

 

[begreen]

I agree completely. There doesn't sound like a huge difference is pipe size there, but a 6" pipe has an area of 28.26sq in. and an 8" pipe has an area of 50.24sq in. That's a good amount more air that would have to be heated in order to give a good draft.

Matt

logic 4 analysis= 6" stove exhaust allows for a 6 or 8" chimney. An 8" stove exhaust disallows a 6" chimney? I'd guess the 8" has better draft.

To a certain extent, but you can reach a point of diminishing returns and beyond that a reversal of performance by increasing the chimney size

reversal of performance from too much draft?

Not quite. A bigger pipe of the same height is going to slow the velocity of flue gases exiting the chimney. That cools the gases. This is not what you want with a flue that is right on the cusp of being tall enough to achieve reasonable draft.

 

[Fsappo]

Someone else will be able to answer this better than I, but as a chimney gets larger than a stove is designed to use..at some point..the stove will have to work harder to create and maintain proper draft during the full curve of a typical wood fire. So, a 6" stove into an 8" chimney in almost every case would work fine..almost every case.

u sell the stoves & got the manuals so do any say not to oversize the chimney?

You can go online and read manuals as easily as I can.

 

[Delta-T]

i'm not sure even the manuals can really figure some of this stuff out. Its hard to account for temperature differential, air pressure, altitude, wind prevalence, and the quanity of gasoline used to start the fire. Thats why in lots of manuals it will say....if it doesn't draft well with 6"....try 7 or 8", or make it taller.

 

[vvvv]

http://extension.missouri.edu/publications/DisplayPub.aspx?P=g1732
long read but FLUE section addresses the issue

 

[tiber]

Alright, instead of comparing our relative pipe sizes, lets ask the million dollar question: "What stoves are you thinking about so that people may offer advice based on specifications and experience?"

 

[dougand3]

From the MO extension site:
"The opening in the chimney through which smoke passes is called the flue. To provide adequate room for smoke passage and draft development, flues must be carefully sized in relation to stove capacity and chimney height. In general, flue size should be 25 percent larger than the size of the stove pipe, which connects the stove to the chimney. This means a stove with a 6-inch diameter pipe would require at least an 8-inch flue; an 8-inch stove pipe requires a 10-inch flue, etc."

That looks like horse hockey to me. How many stove manufacturers say "Stove has 6" flue exit - use 8" pipe and chimney"?

 

[begreen]

Indeed, I haven't had time to read the article, but it sounds like some windbaggery, especially if no regard to height or other consideration was included with that statement.

 

[btuser]

Is the chimney inside or outside? Insulated?