BK Clearance Question?

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tpcolson

Member
Nov 2, 2016
12
tennessee
After reading this forum for years, been looking to get a BK. Looking at their manuals, they depict in their clearances a 2 foot minimum vertical run before the stove pipe does a 90 degree into the wall. All of their stoves. Based on where my thimble is now, with the BK 30, all I can get is 16 inches. Moving the thimble higher (and re-doing the whole chimney) will negate this dream of mine, as it would be cheaper to add a second heat pump and ducting. Chimney installs start at 20k in my neck of the woods. To be clear, I'm talking about the part of the stove that goes up (vertical) then turns into the wall, through a thimble, then to my already existing double wall, insulated, SS chimney (that is not getting replaced). So how far away am I from a BK? I'm assuming an installer won't install if I can't get this clearance, nor can I get insured? I can easily meet, and exceed, by a far margin, all of the other clearance minimums, just not the minimum vertical run before it turns into the wall. Which is odd, as that specific clearance seems to be a manufacturer one, the clearance I see on every safety web site is 12" min before turning into the wall. I'm guessing BK has their own draft requirements, hence the length of the vertical run? Emphasizing that moving the chimney and the thimble has zero chance of ever happening, would require a structural engineer (knocking holes in load bearing exterior wall, and other permit requirements that would likely make it cheaper to build a new house!).
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,199
central pa
After reading this forum for years, been looking to get a BK. Looking at their manuals, they depict in their clearances a 2 foot minimum vertical run before the stove pipe does a 90 degree into the wall. All of their stoves. Based on where my thimble is now, with the BK 30, all I can get is 16 inches. Moving the thimble higher (and re-doing the whole chimney) will negate this dream of mine, as it would be cheaper to add a second heat pump and ducting. Chimney installs start at 20k in my neck of the woods. To be clear, I'm talking about the part of the stove that goes up (vertical) then turns into the wall, through a thimble, then to my already existing double wall, insulated, SS chimney (that is not getting replaced). So how far away am I from a BK? I'm assuming an installer won't install if I can't get this clearance, nor can I get insured? I can easily meet, and exceed, by a far margin, all of the other clearance minimums, just not the minimum vertical run before it turns into the wall. Which is odd, as that specific clearance seems to be a manufacturer one, the clearance I see on every safety web site is 12" min before turning into the wall. I'm guessing BK has their own draft requirements, hence the length of the vertical run? Emphasizing that moving the chimney and the thimble has zero chance of ever happening, would require a structural engineer (knocking holes in load bearing exterior wall, and other permit requirements that would likely make it cheaper to build a new house!).
There is no possible way moving a thimble should cost $20000. That being said this requirement isn't about safety it's about performance. If you have enough overall height it will probably work fine. If you are close to the minimum it won't work properly. What is your overall height?

And I can all but guarantee an installer would do it an inspector wouldn't question it and insurance won't care.
 
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Tjm

New Member
Feb 25, 2021
69
Western NY
If you’re current thimble is between stud bays, I can’t imagine it would be a problem to move it higher unless you’re getting too close to the ceiling? . And you already have the chimney pipe outside. Can’t it be shifted up a foot? Doesn’t sound like a $20k chimney install. Id be hard pressed to spend the kind of money a new woodstove costs without knowing I met the draft and venting requirements unless somehow the dealer was going to accept responsibility for the install and even then…

( I’m familiar with some framing and engineering but not chimneys and clearances … yadda yadda typical disclaimer- just my opinion)
 

stoveliker

Minister of Fire
Nov 17, 2019
2,023
Long Island NY
As this is a requirement meant to provide good draft, you can try to use two 45 deg elbows instead.
 
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Highbeam

Minister of Fire
Dec 28, 2006
19,349
Mt. Rainier Foothills, WA
Does the manual “require” the 2 feet vertical or recommend it? Big difference between shall and should.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
90,660
South Puget Sound, WA
Go with two 45s and an offset. How much chimney height after that point?
 

ABMax24

Minister of Fire
Sep 18, 2019
1,226
Grande Prairie, Alberta, Canada
To me it's further confused by this page, according to this the 2ft height is a BK recommendation but not a requirement. I personally would inquire to Blazeking, if this is truly a recommendation and not a requirement they would likely write you an email stating that, I think this email would appease most inspectors and insurance companies should an issue arise.

Screenshot (175).png
 
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kennyp2339

Minister of Fire
Feb 16, 2014
6,124
07462
All of these recommendations from BK are based off a tested chimney draft of .05" wc during epa testing. That is the minimum draft strength (as is with the majority of new stoves) that the stove will burn cleanly as designed. This .05 number is also established when you have a minimum height of 15ft (Older princess models use to ask for a minimum 12ft chimney height)
The idea of first having 3ft (2ft minimum) straight up from the flue collar before the first 45deg elbow was to limit turbulence of the smoke as it exited the flue collar while running low (we all know that these stove can be burnt at a crazy low level and that flue gas temps are well below other stoves due to that)
The manufacturer will almost never give the thumbs up to installing a stove were the install minimums are not met, but shouldnt stop the OP, the OP just needs a little more help, if the actual chimney run length from stove top to chimney cap exceeds 20ft you should be fine with installing your first 45deg elbow in the 18" range, if you total length is below 20ft then I would want a pro to come out while the old stove is hooked up and do a real draft test to see your number before you invest 4k into a stove.
If you do pull the trigger on the BK, just make sure and be adamant that the black stove pipe is double wall and the only 45deg elbows are used to make the connection from stove collar to class a thimble.
 

tpcolson

Member
Nov 2, 2016
12
tennessee
All of these recommendations from BK are based off a tested chimney draft of .05" wc during epa testing. That is the minimum draft strength (as is with the majority of new stoves) that the stove will burn cleanly as designed. This .05 number is also established when you have a minimum height of 15ft (Older princess models use to ask for a minimum 12ft chimney height)
The idea of first having 3ft (2ft minimum) straight up from the flue collar before the first 45deg elbow was to limit turbulence of the smoke as it exited the flue collar while running low (we all know that these stove can be burnt at a crazy low level and that flue gas temps are well below other stoves due to that)
The manufacturer will almost never give the thumbs up to installing a stove were the install minimums are not met, but shouldnt stop the OP, the OP just needs a little more help, if the actual chimney run length from stove top to chimney cap exceeds 20ft you should be fine with installing your first 45deg elbow in the 18" range, if you total length is below 20ft then I would want a pro to come out while the old stove is hooked up and do a real draft test to see your number before you invest 4k into a stove.
If you do pull the trigger on the BK, just make sure and be adamant that the black stove pipe is double wall and the only 45deg elbows are used to make the connection from stove collar to class a thimble.
Thanks. Run from Stove to Cap is closer to 30 feet, maybe 35. It's 20-ish inches from the top of current stove to where it turns into thimble, 2-ish feet to the thimble, then to pipe outside and straight run to the cap above the roof. Pretty simple, all things considered.

As to the other replies, thanks, but the chimney or the thimble not getting moved. Thimble is through hollow cbu wall. Moving it up 1 foot will still keep me well in excess of distance to ceiling minimums. Here's why it's not getting moved: When the house was built, the thimble was installed simply by knocking a thimble-sized hole in the wall. Codes and permit requirements have since changed, and any concrete/CBU penetration greater than I think 6 " requires a "Lintel" (header, solid piece of rebar enforced concrete spanning 2X the opening), doubly-so since I'm putting a big hole directly above an existing hole. This requires bringing in those guys that jack up and support houses when foundation work is done. Then there's filling in/repairing the old thimble hole. Absolutely not worth it. If this was solid form-poured concrete....maybe....but a hollow cbu wall installed by someone who had no business laying cbu's.....no way....

I'll give BK a call, but it looks dubious. My insurance requires a cleaning/inspection every 3 years, and they come armed with all the stove manuals on a tablet. Any manufacturer-required clearance not met, stove has to come out or find new insurance. Currently have a 30 year old buck stove that will deforest the county at the rate at which it burns wood, looking to go to the opposite end of efficiency. Stacked 6 cords this weekend thinking I need to get a better stove, I'm sick of doing this every year! The quadrupling of firewood prices, in the rare instance you can actually find someone who has firewood is also a motivation to get a more efficient stove.
 

stoveliker

Minister of Fire
Nov 17, 2019
2,023
Long Island NY
Again, this is not a clearance (safety) issue, it is a requirement/recommendation to ensure there is enough draft to operate the stove in its design specifications.

30 ft should make this all a non-issue.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
26,199
central pa
Thanks. Run from Stove to Cap is closer to 30 feet, maybe 35. It's 20-ish inches from the top of current stove to where it turns into thimble, 2-ish feet to the thimble, then to pipe outside and straight run to the cap above the roof. Pretty simple, all things considered.

As to the other replies, thanks, but the chimney or the thimble not getting moved. Thimble is through hollow cbu wall. Moving it up 1 foot will still keep me well in excess of distance to ceiling minimums. Here's why it's not getting moved: When the house was built, the thimble was installed simply by knocking a thimble-sized hole in the wall. Codes and permit requirements have since changed, and any concrete/CBU penetration greater than I think 6 " requires a "Lintel" (header, solid piece of rebar enforced concrete spanning 2X the opening), doubly-so since I'm putting a big hole directly above an existing hole. This requires bringing in those guys that jack up and support houses when foundation work is done. Then there's filling in/repairing the old thimble hole. Absolutely not worth it. If this was solid form-poured concrete....maybe....but a hollow cbu wall installed by someone who had no business laying cbu's.....no way....

I'll give BK a call, but it looks dubious. My insurance requires a cleaning/inspection every 3 years, and they come armed with all the stove manuals on a tablet. Any manufacturer-required clearance not met, stove has to come out or find new insurance. Currently have a 30 year old buck stove that will deforest the county at the rate at which it burns wood, looking to go to the opposite end of efficiency. Stacked 6 cords this weekend thinking I need to get a better stove, I'm sick of doing this every year! The quadrupling of firewood prices, in the rare instance you can actually find someone who has firewood is also a motivation to get a more efficient stove.
What code states that requirements about a lintel? And are you talking about a CMU concrete block wall? CBU always meant concrete backer in my training. But even with adding a lintel that is an hour's work moving the whole chimney up would take longer obviously but the total bill might hit 1500 at most. And I would be surprised if it took a whole day.

If you don't want to move the thimble that is perfectly fine. If your chimney is 30' you will not have a problem with under draft at all. You will have to much draft for sure.
 
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tpcolson

Member
Nov 2, 2016
12
tennessee
What code states that requirements about a lintel? And are you talking about a CMU concrete block wall? CBU always meant concrete backer in my training. But even with adding a lintel that is an hour's work moving the whole chimney up would take longer obviously but the total bill might hit 1500 at most. And I would be surprised if it took a whole day.

If you don't want to move the thimble that is perfectly fine. If your chimney is 30' you will not have a problem with under draft at all. You will have to much draft for sure.
So it's a draft requirement not a safety requirement? I guess the question is....anyone have a BK installed professionally and not have that 2 feet from stove top to thimble? I might even have more than 30 feet, there was an issue with clearance and height above the top of the roof or something that they dealt with on the first cleaning/inspection that resulted in it being taller/longer. Think they added a foot or 2. Stove is in a finished "basement" of a two-story log cabin, with your traditional steep pitch roof, pipe goes outside wall, through the roof overhang on side of house or whatever it's called, and the cap is slightly above the peak of the roof. It's high enough where I have to put some kind of wind braces or something on it to prevent wind from blowing it over (according to the inspector).

The only time i have draft issues is when lighting off a cold stove which is easily solved and never presents much of a problem. Once it gets going it drafts fine and as you say, perhaps a little too good, if I get it going really good the draft rattles the door inserts if I have the damper wide open.

I've always called cinder blocks "CBU". Adding a lintel involves knocking out a full block on either side of the proposed opening as well as whatever is required for the opening. A lintel weighs about 500 lbs. And I've already asked, requires a stamped engineering design in my jurisdiction for any load bearing wall penetrations. Sometimes I wonder if building codes make anyone safer when they make them so onerous and expensive forcing more people to avoid them all together by just "doing it". Unfortunately I live in one of those areas where the inspector seemingly has eyes everywhere. He'll make you tear an entire deck down if you didn't do a footer inspection. The lintel requirement has been part of IRC and IBC for a pretty long time, not sure of the exact language, but "masonry over openings shall be supported" has been a thing for as long as I can remember, but apparently not at the time when this house was built.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,199
central pa
So it's a draft requirement not a safety requirement? I guess the question is....anyone have a BK installed professionally and not have that 2 feet from stove top to thimble? I might even have more than 30 feet, there was an issue with clearance and height above the top of the roof or something that they dealt with on the first cleaning/inspection that resulted in it being taller/longer. Think they added a foot or 2. Stove is in a finished "basement" of a two-story log cabin, with your traditional steep pitch roof, pipe goes outside wall, through the roof overhang on side of house or whatever it's called, and the cap is slightly above the peak of the roof. It's high enough where I have to put some kind of wind braces or something on it to prevent wind from blowing it over (according to the inspector).

The only time i have draft issues is when lighting off a cold stove which is easily solved and never presents much of a problem. Once it gets going it drafts fine and as you say, perhaps a little too good, if I get it going really good the draft rattles the door inserts if I have the damper wide open.

I've always called cinder blocks "CBU". Adding a lintel involves knocking out a full block on either side of the proposed opening as well as whatever is required for the opening. A lintel weighs about 500 lbs. And I've already asked, requires a stamped engineering design in my jurisdiction for any load bearing wall penetrations. Sometimes I wonder if building codes make anyone safer when they make them so onerous and expensive forcing more people to avoid them all together by just "doing it". Unfortunately I live in one of those areas where the inspector seemingly has eyes everywhere. He'll make you tear an entire deck down if you didn't do a footer inspection. The lintel requirement has been part of IRC and IBC for a pretty long time, not sure of the exact language, but "masonry over openings shall be supported" has been a thing for as long as I can remember, but apparently not at the time when this house was built.
So your jurisdiction requires a stamped engineered drawing for any penetration in your foundation wall? Even if that is true there is no way you will get to $20000.

And yes I am fully aware of what it takes to put a lintel in I have put in enough windows doors etc. I am telling you even if you have to put a lintel in (which I seriously doubt) it is an hour of work or so. It isn't a big deal at all.

I am really curious what the code you are quoting is. Because I have been doing this a long time and put or installed chimneys in hundreds of holes in foundations that were inspected and no one ever mentioned a lintel.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,660
South Puget Sound, WA
With 30ft of stack this seems like a non-issue. If anything it sounds like a key damper may be needed to reduce draft unless this is a known negative pressure area.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
26,199
central pa
With 30ft of stack this seems like a non-issue. If anything it sounds like a key damper may be needed to reduce draft unless this is a known negative pressure area.
I agree completely. I am just curious about this code requirement now. If I am doing it wrong I want to know. I don't mind putting a lintel in if required.
 

Tjm

New Member
Feb 25, 2021
69
Western NY
So at what point do you have too much draft? Is there a chance with a 30 ft chimney, he won’t be able to throttle down the blaze king in the way they’re known to perform?
 

stoveliker

Minister of Fire
Nov 17, 2019
2,023
Long Island NY
With a key damper (or two) you can make it work.

I have a similar situation. 20" up, 90 deg elbow, 2' horizontal, 27' up. Works like a charm here.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,660
South Puget Sound, WA
So at what point do you have too much draft? Is there a chance with a 30 ft chimney, he won’t be able to throttle down the blaze king in the way they’re known to perform?

When the draft exceeds the recommended range in the manual it may need to be reduced with a damper.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,349
Mt. Rainier Foothills, WA
If the penetration in your cmu wall needed to have a lintel then how will your existing penetration not trigger that requirement? Is the new stove a trigger?

With 30’ of stack, even though it is outside and has a bends, I would expect 18” to be sufficient to provide sufficient if not excessive draft while operating. The challenge, as you found with the current stove, is getting the cold chimney moving at startup.

Measuring draft is done at high fire, so hitting the spec on a cold chimney is not possible or relevant. It’s an added challenge to burn efficiently, safely, and smoke free on an excessively long or excessively short chimney but we can’t all have 15’ vertical stacks.
 
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Highridgefire

New Member
Mar 1, 2021
4
Kentucky
Just wanted to chime in and say I had the exact same situation as you.


A blaze king was my dream stove install, And I like you did not have much vertical rise before going into my Masonary thimble.

The cost to move my thimble would not have been cheap.

I called blaze king twice, spoke with two people there and they literally said “please do not buy this stove”



So I did even more research and learned about the difference between stoves that exit straight up, and stoves that draft out the back. Stoves that draft out the back will not have this height requirement because it is a different type of set up inside the box.

Long story short we went with the jotul 500. My wife was pleased because she likes the look better. I’m a little disappointed I can’t get those crazy 30 hour burn times but the yodel still does very well and I think it drafts very good for my set up and I didn’t even need a liner which really surprised me because my clay liner is a larger diameter. But again Jotul was the only brand that still said my larger size chimney was still compatible.