What good is an 8" stove pipe?

[EmeraldAshBurner]

Hi folks,

I've been reading the forums here about 6" and 8" stove pipe and I still could use some clarification/advice.

I'm installing an old (free) stove in a shop type situation. It has an 8" outlet on top but in forums here people are saying that 6" pipe actually draws better. And it's much easier for me to source 6" components at my local Lowe's. 8" stuff needs to be special ordered, and I actually got started with 8" but now I'm having second thoughts (I could return some of what I have).

The indoor single-wall pipe would go about 12.5-13' to the ceiling, followed by 4' of double-wall stainless through the roof.

One final hitch is that I already installed a cathedral ceiling support for an 8" pipe through the roof. Should I just finish up my installation with 8" all the way and quit thinking about it? I'd need to order parts but there's no rush. Is there any advantage (or disadvantage) to having 6" for the interior and 8" through the roof?

 

[begreen]

An old smoke dragon is not going to be too fussy.

 

[bholler]

Hi folks,

I've been reading the forums here about 6" and 8" stove pipe and I still could use some clarification/advice.

I'm installing an old (free) stove in a shop type situation. It has an 8" outlet on top but in forums here people are saying that 6" pipe actually draws better. And it's much easier for me to source 6" components at my local Lowe's. 8" stuff needs to be special ordered, and I actually got started with 8" but now I'm having second thoughts (I could return some of what I have).

The indoor single-wall pipe would go about 12.5-13' to the ceiling, followed by 4' of double-wall stainless through the roof.

One final hitch is that I already installed a cathedral ceiling support for an 8" pipe through the roof. Should I just finish up my installation with 8" all the way and quit thinking about it? I'd need to order parts but there's no rush. Is there any advantage (or disadvantage) to having 6" for the interior and 8" through the roof?

6" pipe doesn't draw better. It draws differently. It can carry much less volume than 8" pipe so it really depends on the needs of your stove.

 

[St. Coemgen]

I've been reading the forums here about 6" and 8" stove pipe and I still could use some clarification/advice.

Well... it may depend. Check, you local codes. They may have chimney height versus appliance size that determine flue diameter rules (or not... so check).

Example (only an example --- again check your local codes) :

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[EmeraldAshBurner]

6" pipe doesn't draw better. It draws differently. It can carry much less volume than 8" pipe so it really depends on the needs of your stove.

Is it as simple as bigger stove = bigger pipe? I have a feeling it's not quite that simple. But if the stove has an 8" outlet does that basically answer the question (i.e. use an 8" pipe) or is there more to consider?

 

[EmeraldAshBurner]

I appreciate the replies. I'm still not sure I have a great grasp on it but I think I will complete the installation with 8" pipe and hope for the best.

 

[bholler]

Is it as simple as bigger stove = bigger pipe? I have a feeling it's not quite that simple. But if the stove has an 8" outlet does that basically answer the question (i.e. use an 8" pipe) or is there more to consider?

Pretty much you should match the pipe to the stove. Now with older stoves many times there really wasn't much engineering done with many of them so some would work fine on smaller chimneys. We just don't know

 

[Highbeam]

I wouldn’t do 8” unless your dream stove is an 8” like a BK king. Go 6”. All currently legal modern wood furnaces use 6”. All but just a few current stoves use 6”.

I have a very similar shop chimney and it’s 6”. My stove is a cheap modern stove but it’s been great and it’s 6”.

One more thought.. single wall runs over 10’ can be trouble. I used single wall and wish I had used double wall.

 

[peakbagger]

VC Defiant's were designed for 8", They would run with 6" with ideal draft conditions but they really were not happy until up to temp. They also could be run with the front doors open with a wire grille. That option really needed a 8" pipe when cold.

It is interesting to me that my 35 year old 100,000 BTU Burnham wood boiler has an 8" while my recently acquired (not yet installed) 140,000 BTU Tarm boiler has a 6" outlet. The difference is the Burnham is natural draft while the Tarm has a fan on it.

One thing that a lot of folks do not think about is water vapor increasing the volume of exhaust gases. Smoke dragons needed a bigger stack to deal with marginally dry wood. Water vapor takes up a lot of room and the vast majority of water in the wood has to be converted to vapor and sent up the stack. A modern stove was designed for dry wood, its using the draft pressure harder to crank up velocities in various combustion gas and air streams to enhance turbulence. Add in damp wood and the draft is used up by dealing with the extra volume of water vapor. Note the water vapor is also eating up a minimum of 1000 btus/lb of water to convert from the liquid water in the wood to vapor.

 

[stoveliker]

It'd be good to post what stove you have...?

 

[Dave_in_ABQ]

Is it as simple as bigger stove = bigger pipe? I have a feeling it's not quite that simple. But if the stove has an 8" outlet does that basically answer the question (i.e. use an 8" pipe) or is there more to consider?

Pretty much. To 1st order (unless you miss-size your flue significantly) draft corresponds to chimney height, volume of burn gasses to diameter. Newer stoves can use smaller diameter flues because they get the same heat output burning less wood. I'd say since you already cut a hole in your roof and installed an 8" chimney, it doesnt make sense to put in a 6" stove pipe with 6" to 8" adapters at both ends. That and your old stove may actually do better with an 8" flue - back to the question which stove do you have? - which is a better place to start anyway.

 

[Highbeam]

You already cut the roof? You’re stuck now.

 

[EmeraldAshBurner]

You already cut the roof? You’re stuck now.

I didn't cut the roof yet but I did frame in the cathedral ceiling support, so if I switched to 6" I'd have to reframe and install a different one. That's the only thing I've done so far besides buy stuff that can be returned.

 

[EmeraldAshBurner]

I haven't seen any identifying marks on the stove but I can look harder and/or post a picture.

It'd be good to post what stove you have...?

 

[Highbeam]

I didn't cut the roof yet but I did frame in the cathedral ceiling support, so if I switched to 6" I'd have to reframe and install a different one. That's the only thing I've done so far besides buy stuff that can be returned.

Okay, that's good and easily reversible. 8" is obsolete and archaic. It's like spending a bunch of money on a dwell meter to adjust the points in your car's ignition system. If you dream of a car with points, it's required but otherwise not. That old 8" stove you have is an old stove and that's why it's 8".

 

[EmeraldAshBurner]

Okay, that's good and easily reversible. 8" is obsolete and archaic. It's like spending a bunch of money on a dwell meter to adjust the points in your car's ignition system. If you dream of a car with points, it's required but otherwise not. That old 8" stove you have is an old stove and that's why it's 8".

You're saying that the stove doesn't know better and it would do just as well or better with a 6" pipe.

 

[bholler]

You're saying that the stove doesn't know better and it would do just as well or better with a 6" pipe.

We have no idea. We don't know what stove it is

 

[Highbeam]

You're saying that the stove doesn't know better and it would do just as well or better with a 6" pipe.

No, I'm saying the only good that an 8" chimney will do for you is to work well with the current/temporary/old probably illegal smoke dragon that you currently own. The stove you upgrade to will almost (like 99%) certainly be 6" and the 8" will be either prohibited by the owner's manual (making it an illegal install) or less desirable so it might kinda work okay.

I had a big 8" fisher stove to install in my current shop. Before I wasted money and effort on an 8" chimney I was smart enough to sell it and invest in a modern, high efficiency, low emissions stove with a window. It's a big stove and uses a 6" chimney. Installing that 8" fisher would have been illegal in my state since it is an old, archaic, obsolete, smoke dragon without EPA certification.

The biggest regency and BK king are nice stoves that use an 8" stack and are currently legal to install. If the stove that you currently own was one of those then maybe the 8" is worth it. Not to make some old smoke dragon work. IMO of course.

 

[EmeraldAshBurner]

No, I'm saying the only good that an 8" chimney will do for you is to work well with the current/temporary/old probably illegal smoke dragon that you currently own. The stove you upgrade to will almost (like 99%) certainly be 6" and the 8" will be either prohibited by the owner's manual (making it an illegal install) or less desirable so it might kinda work okay.

I had a big 8" fisher stove to install in my current shop. Before I wasted money and effort on an 8" chimney I was smart enough to sell it and invest in a modern, high efficiency, low emissions stove with a window. It's a big stove and uses a 6" chimney. Installing that 8" fisher would have been illegal in my state since it is an old, archaic, obsolete, smoke dragon without EPA certification.

The biggest regency and BK king are nice stoves that use an 8" stack and are currently legal to install. If the stove that you currently own was one of those then maybe the 8" is worth it. Not to make some old smoke dragon work. IMO of course.

Okay thanks. I see what you're saying. I may install this stove now because it's free, but I'd probably be better off making my chimney pipe 6" because any stove I might replace it with later (not unlikely that I would) would want the 6" pipe. And I can make do for now with an adapter for my smoke dragon. Or that's one way to look at it, at least.

 

[Highbeam]

Okay thanks. I see what you're saying. I may install this stove now because it's free, but I'd probably be better off making my chimney pipe 6" because any stove I might replace it with later (not unlikely that I would) would want the 6" pipe. And I can make do for now with an adapter for my smoke dragon. Or that's one way to look at it, at least.

I don't know that I would even bother installing that 8" stove. Another problem with old stoves like that is that you need huge clearances to combustibles so the thing will take up a huge amount of floor space. The modern stove will be able to set very close to the wall. You always want your chimney to be run vertically if possible with no bends so locating it above the 8" monster is the wrong place for the modern 6" stove.

One advantage to that old 8" stove other than cost is that they do get really hot and are quite durable. There's not a lot to go wrong in the steel box.

Seriously, I sold that fisher for like 500$. Bought a new, certified, warrantied, with a window, clean burning, efficient, NC30 from home depot for under $800 delivered. There should even be some used but modern and EPA certified stoves available for you.

 

[bholler]

I don't know that I would even bother installing that 8" stove. Another problem with old stoves like that is that you need huge clearances to combustibles so the thing will take up a huge amount of floor space. The modern stove will be able to set very close to the wall. You always want your chimney to be run vertically if possible with no bends so locating it above the 8" monster is the wrong place for the modern 6" stove.

One advantage to that old 8" stove other than cost is that they do get really hot and are quite durable. There's not a lot to go wrong in the steel box.

Seriously, I sold that fisher for like 500$. Bought a new, certified, warrantied, with a window, clean burning, efficient, NC30 from home depot for under $800 delivered. There should even be some used but modern and EPA certified stoves available for you.

I don't know for a shop a big old beast of a stove isn't a bad choice.

 

[Highbeam]

I don't know for a shop a big old beast of a stove isn't a bad choice.

Some people really do like some of those old beasts and can burn them pretty clean. The lack of a clean window would be a big downer for me. I spend a lot of time in the shop enjoying the window.

 

[bholler]

Some people really do like some of those old beasts and can burn them pretty clean. The lack of a clean window would be a big downer for me. I spend a lot of time in the shop enjoying the window.

No way would I put one in my home. But I have one on my shop

 

[Highbeam]

No way would I put one in my home. But I have one on my shop

If the alternative was a barrel stove, I would gladly take the big fisher.

 

[bholler]

If the alternative was a barrel stove, I would gladly take the big fisher.

Very true.