Chimney Pipe 6" to 8"

[banginglc1]

Let me set the scenario. We are putting in a new install wood stove. The room is like a barn, almost 30ft at chimney exit near the center of the vaulted ceiling. Pipe will all be inside until roof exit. only a couple of feet will be needed above the roof line. It will heat the giant room (approx 30' x 30') plus some other areas of the house that are connected in a fairly open floor plan.

Due to budget, I picked up a used wood stove that isn't as large as we wanted (we want a big one to heat that space plus other parts of the house). It has a 6" flue. We plan on replacing it in a couple years when we have the budget for a larger and nicer stove. I have a chimney installer coming to do the chimney. I'm too scared of heights to do it and our insurance needs someone certified to sign off anyways. He wants to use 8" pipe. He said a lot of the large stoves we might want may use and it would be good to have. He said since we have such a long run inside to not worry about the draft. I'm just concerned that 8" is too big. It seems most newer stoves use 6", even the big ones.

Should I pressure him to go 6" or would the 8" be more universal for future needs. I'm less concerned about this stove than the future ones, we'll make do for this stove.

 

[EbS-P]

Only a handful of stoves use 8”. I can’t list more than 5. They are big 4+cu ft. 6” will be much cheaper and give more options. Look at the 8” stoves now. Regency, buck, Blaze king, I might be missing one. Rule them In or out and make the call 6” or 8”.

 

[Todd]

How many sq ft are you trying to heat? There are some large stoves out there that run on 6”. The only two stoves I can think of that use 8” is Blaze King King and Regency 5200.

 

[stoveliker]

Also, a tall flue like that might need a key damper (regardless of its diameter). Most stoves work best between 15 and 20 ft (when no elbows, and not at elevation). I would have a key damper installed when [whatever you put in] gets installed.

 

[kennyp2339]

I’d go with the 8”, install 2 key dampers in the 6” pipe and roll on.

 

[begreen]

What is the used stove make and model?

Also, a tall flue like that might need a key damper (regardless of its diameter). Most stoves work best between 15 and 20 ft (when no elbows, and not at elevation). I would have a key damper installed when [whatever you put in] gets installed.

And the stovepipe should be double-wall. 30' of single-wall will cool down the flue gases extensively, potentially leading to excess creosote buildup in the chimney.

 

[stoveliker]

Yes, though it (the pipe) is all inside, here.
Regardless, modern stoves do better with double wall pipe. You want the heat from the stove, and if the stove is efficient, very little goes up the pipe. You don't want that to cool down much more.

 

[begreen]

Stovepipe is always inside. It is not permitted outside of the room envelope. Many stove manufacturers now add the caveat in their manuals that single-wall stovepipe should not exceed 8' in length.

 

[stoveliker]

You are of course correct. Slip of the mind here.

 

[Ashful]

Only a handful of stoves use 8”. I can’t list more than 5. They are big 4+cu ft. 6” will be much cheaper and give more options. Look at the 8” stoves now. Regency, buck, Blaze king, I might be missing one. Rule them In or out and make the call 6” or 8”.

I think you got nearly all of the ones I know, unless JA Roby is still making their enormous beast (4.4 cu.ft.?).

 

[kennyp2339]

I’m taking in the fact that the OP had a ton of airspace that needs to be heated, I’d go big or set the foundation of going big, class a and smoke pipe is expensive and something that I’d only want to do once or twice for the life of the stove area.

 

[begreen]

I think you got nearly all of the ones I know, unless JA Roby is still making their enormous beast (4.4 cu.ft.?).

I don't think it made the EPA 2020 cut. That beastie had a 6" flue IIRC and a usable firebox of more like 3.5 cu ft.

 

[Ashful]

I don't think it made the EPA 2020 cut. That beastie had a 6" flue IIRC and a usable firebox of more like 3.5 cu ft.

Really? That’s a surprise. I remember some of the marketing at the time indicating it was the largest (pre-2020) EPA stove on the market? Have to admit I never paid a lot of attention to it, but I remember one member with an enormous having one, and some claims it was even bigger than the BK King that he was considering.

 

[begreen]

Definitely 6" vent. From what I recall, the 4.6 cu ft dimensions came from the full firebox side including above the baffle. The firebox was sloped at the bottom front and I think only 4 firebricks wide or 18" at the back. It got wider in the front to maybe 20 or 21"?

 

[Ashful]

Definitely 6" vent. From what I recall, the 4.6 cu ft dimensions came from the full firebox side including above the baffle. The firebox was sloped at the bottom front and I think only 4 firebricks wide or 18" at the back. It got wider in the front to maybe 20 or 21"?

Got it. Yeah, I wasn't questioning the vent size, just the firebox volume, as something around 4-1/2 cu.ft. had stuck in my head. Your explanation makes sense, though.

 

[banginglc1]

Thanks for the help. He was fine doing 6”. It makes the most sense with what we have and. Want I the future. Double wall was always the plan. 1 week from tomorrow we should be up and running.

What exactly do key dampers in the pipe do? I’ll do more research as soon as I hit submit on this post, but will always take more info.

Thanks again

 

[banginglc1]

6” is being installed. What would you use 2 keys dampers? How far would you space them?

 

[kennyp2339]

For longer flue runs the key dampers add turbulence which slows draft down (think of a speedbump in a road) 2 dampers spaced a foot apart works well if your draft is high (I have high draft issues when a north wind blows by me)
I suggested the (2) dampers because I thought you were installing 8" pipe then going to 6" length for the current stove, the volume of 8" pulling for 25ft would have sucked the ash in your stove right out (being dramatic here for effect)

 

[begreen]

Thanks for the help. He was fine doing 6”. It makes the most sense with what we have and. Want I the future. Double wall was always the plan. 1 week from tomorrow we should be up and running.

What exactly do key dampers in the pipe do? I’ll do more research as soon as I hit submit on this post, but will always take more info.

Thanks again

Out of curiosity, what stove is going in?

One key damper may suffice. For double-wall stovepipe, it should ideally be in a factory double-wall section of pipe. This is usually a 6" section and this could be the starter section off of the stove's flue collar.

 

[Ashful]

For a reference point, I have about 30 feet of 6” insulated pipe off one of my Ashfords, and a single key damper does it just fine. I have to turn it fully closed to hold my optimum .05” WC on high setting in some weather conditions, but there has never been a case where I’ve wished I had a second.

Kenny was basing his ‘em recommendation on your described 6” to 8” transition, and that may change the equation a little, but I’d think not that much. I’d try one, until proven you need a second. They’re easy to add later.

 

[banginglc1]

US Stove Model 2007 is what's going in (picked it up for $100, good condition). The manual shows I can add one in the flue collar, which I'll do unless my installer has a better suggestion.

 

[kennyp2339]

Be minful those stoves are single rate burners (no air control) and can have a mind of there own under certain stronger draft conditions

 

[banginglc1]

Be minful those stoves are single rate burners (no air control) and can have a mind of there own under certain stronger draft conditions

would that be reason enough to add a 2nd damper preemptively for more control?

 

[EbS-P]

would that be reason enough to add a 2nd damper preemptively for more control?

I’d do the collar and another one in case you swap stoves. The second will will then become the only. Most stoves don’t install dampers in the collar

 

[begreen]

Be minful those stoves are single rate burners (no air control) and can have a mind of there own under certain stronger draft conditions

Good catch. This is an old 35:1 stove, it must have a flue damper to control the burn. 2 may be required with this tall flue system.