# Relationship between chimney draft and height



## dafattkidd (Oct 11, 2013)

Hey,

Admittedly my install is not bulletproof.  I have about 14 feet from the bottom of my unit to the top of my chimney so probably like 12" of actual chimney liner.  My insert heats fantastically, efficiently and burns cleanly. I try to burn good dry wood as best as I can.

My problem is every time I open the door I get smoke in the house.  And not just a a quick whiff, like it pours in the room.  I have an offset box that attaches the insert to the chimney.  I'm fairly sure the offset box is the culprit, but it's a necessary evil without extensive masonry work. Last year I replaced the offset box and used furnace cement to seal any suspicious air gaps.  It had no improvement. 

Here's my question: will increasing the length of my chimney by 3 feet help?  

Here's my version of the math: 12 ft chimney + 3 ft (25%) increases draft by 25%.  Is this correct?  Will adding three feet really increase my draft and help with this?  And if so what is the best product to transition a 6" SS flex liner to class A chimney (or whatever is best here)? Thanks so much.


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## Sprinter (Oct 11, 2013)

dafattkidd said:


> Hey,
> 
> Admittedly my install is not bulletproof.  I have about 14 feet from the bottom of my unit to the top of my chimney so probably like 12" of actual chimney liner.  My insert heats fantastically, efficiently and burns cleanly. I try to burn good dry wood as best as I can.
> 
> ...


I'm no expert on this, but I have heard that it is that kind of direct proportion.  A 25% increase in chimney height should help a lot.  I'll leave the rest of the question to others.


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## oldspark (Oct 11, 2013)

3 feet will help and if you need it add another 3 feet if you are not happy with the first 3 feet, might have to support is but sounds like the best solution for what you have, I have 18 feet total straight up and never get smoke back into the house.
Maybe buy a section of 4 feet to give just a little more height, maybe more bang for your buck too.


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## Woody Stover (Oct 11, 2013)

Stick a piece of stove pipe up there to see what happens.

How much minimum stack height does the manual call for?


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## Bluerubi (Oct 11, 2013)

What type of cap do you have on your liner?  Mine was the original round one that came with the kit that had a bunch of slits in the metal to keep out critters.  Draft was pretty good, but after replacing it with a giant cage that covers the whole top of my chimney I've been battling with too much draft, even in warm temps outside.  Thinking back I had about 28 square inches of cross sectional area in my liner, that was choked back to a fraction of that due to the restrictive cap, so I guess I shouldn't be surprised that it pulls a lot stronger now that it's wide open.


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## Jags (Oct 11, 2013)

Three feet can have drastic effects in some instances.  I can tell you that a 2 ft extension to mine virtually _fixed_ an occasional backdraft issue (due to house layout and prevailing winds, not length of flue).  Grab a cheap piece of galv. snap together stuff used for venting.  Stick in on top of what you have.  This is a cheap (and very temporary) way to test your theory.


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## oldspark (Oct 11, 2013)

Bluerubi said:


> What type of cap do you have on your liner?  Mine was the original round one that came with the kit that had a bunch of slits in the metal to keep out critters.  Draft was pretty good, but after replacing it with a giant cage that covers the whole top of my chimney I've been battling with too much draft, even in warm temps outside.  Thinking back I had about 28 square inches of cross sectional area in my liner, that was choked back to a fraction of that due to the restrictive cap, so I guess I shouldn't be surprised that it pulls a lot stronger now that it's wide open.


 
Do you have a link to that product, sounds interesting.


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## AnalogKid (Oct 11, 2013)

Is your liner insulated?  I had a big concern last year when I decided to install my insert.  My chimney is very short, 12'5" from firebox floor to top of chimney.  Mfg told me they recommended 15' at a minimum.  I took a gamble, and with the advice of guys on here, I insulated the heck out of my liner.  I have outstanding draft and zero spillage.


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## dafattkidd (Oct 11, 2013)

Woody Stover said:


> Stick a piece of stove pipe up there to see what happens.
> 
> How much minimum stack height does the manual call for?


 
I'm almost positive it calls for 15" chimney.


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## dafattkidd (Oct 11, 2013)

AnalogKid said:


> Is your liner insulated?  I had a big concern last year when I decided to install my insert.  My chimney is very short, 12'5" from firebox floor to top of chimney.  Mfg told me they recommended 15' at a minimum.  I took a gamble, and with the advice of guys on here, I insulated the heck out of my liner.  I have outstanding draft and zero spillage.


 
I have insulation at the top foot and bottom foot of an interior chimney.


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## dafattkidd (Oct 11, 2013)

Jags said:


> Three feet can have drastic affects in some instances.  I can tell you that a 2 ft extension to mine virtually _fixed_ an occasional backdraft issue (due to house layout and prevailing winds, not length of flue).  Grab a cheap piece of galv. snap together stuff used for venting.  Stick in on top of what you have.  This is a cheap (and very temporary) way to test your theory.


 
Just 6" galvanized chimney like on an oil burner? Will that really give me a pretty accurate idea of the effects?


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## AnalogKid (Oct 11, 2013)

dafattkidd said:


> I have insulation at the top foot and bottom foot of an interior chimney.


How much of a chore would it be to pull your liner?  It may be worth a shot to do a double-wrap on your liner.  I bet it would help.


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## Jags (Oct 11, 2013)

dafattkidd said:


> Just 6" galvanized chimney like on an oil burner? Will that really give me a pretty accurate idea of the effects?



Yep - the $3.00 per 3 ft stuff at the box store.  It will simulate (temporarily) a 3ft extension of pipe well enough to give you an idea if it will work or not.


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## MDFisherman (Oct 11, 2013)

I added a 1ft "dirt leg" I will call, it to the bottom of my flue at the cleanout tee, as the manufacturer recommended.  Do you count this in the overall height of the flue?  what about the pipe inside the house, does the vertical run also count toward the overall flue length?


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## Jags (Oct 11, 2013)

Overall length is usually figured from the Top Base of the stove, to the Top of the pipe where the cap attaches.


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## mellow (Oct 11, 2013)

Per ICC:  The _height_ of the _chimney_ shall be measured from the _firebox_ floor to the top of the _chimney flue._


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## mellow (Oct 11, 2013)

Those offset boxes are horrible, but in some cases it is a nessary evil.

If adding the 3 feet of pipe doesn't work you could look into getting an Enervex Fan to help your draft.


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## Jags (Oct 11, 2013)

Yep - looks like from the base (thanks Mellow).  This from the Quad instal manual.


Chimney Height / Rise and Run
This product was designed for and tested on a 6 inch
( 152 mm) chimney, 12 to 14 feet ( 420 - 480 cm) high, ( includes
stove height) * measured from the base of the appliance *to
the the top of the chimney ( not including chimney cap) .


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## dafattkidd (Oct 11, 2013)

If that's case then my chimney height is closer to 13, but I'm telling you the offset box really makes a mess of things.

I'm going to try the test once it's cool enough to start burning.

Does any one know if there is an equation or a rule of some sort which specifically outlines the relationship between height and draft? Just good to know.


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## mellow (Oct 11, 2013)

It would probably need to be converted into bars of vacuum,  which you would need to have a meter to test.


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## dafattkidd (Oct 11, 2013)

mellow said:


> Those offset boxes are horrible, but in some cases it is a nessary evil.
> 
> If adding the 3 feet of pipe doesn't work you could look into getting an Enervex Fan to help your draft.


 
I would honestly prefer the fan over the extended height. The extra pipe coming out of my chimney will look ridiculous. I am almost positive I have read Begreen express serious reservations about draft induced fans. Any feedback on the fans?


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## oldspark (Oct 11, 2013)

"Taller chimneys usually produce stronger draft. A rule of thumb for minimum height states that the total system height (from the floor the appliance is mounted on to the top of the chimney) should never be less than 4.6 m (15 ft.). Most normal installations exceed this height, but installations in cottages with shallow-pitch roofs may not. If draft problems are experienced with short systems, consider adding to the chimney height. If draft problems are experienced with systems higher than the recommended minimum system height, adding to the chimney may have little or no effect. Most draft problems have to do with inadequate gas temperature in the chimney"


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## Jags (Oct 11, 2013)

Sparky - you bring up a good point.  We haven't had the discussion yet on run temps.  What kind of temps are you running at when you experience the spillage?


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## dafattkidd (Oct 11, 2013)

oldspark said:


> "Taller chimneys usually produce stronger draft. A rule of thumb for minimum height states that the total system height (from the floor the appliance is mounted on to the top of the chimney) should never be less than 4.6 m (15 ft.). Most normal installations exceed this height, but installations in cottages with shallow-pitch roofs may not. If draft problems are experienced with short systems, consider adding to the chimney height. If draft problems are experienced with systems higher than the recommended minimum system height, adding to the chimney may have little or no effect. Most draft problems have to do with inadequate gas temperature in the chimney"


 
Thanks for that. Where is that from?


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## mellow (Oct 11, 2013)

I will say that I got smoke spillage from my insert until I pulled my flex liner and put insulation on it,  but I have a few differences,  exterior chimney, no offset box, 23 ft tall chimney.


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## dafattkidd (Oct 11, 2013)

I generally run my unit pretty hot. 500-700 range is normal. I get spillage pretty much always. I think last year we had a couple of super cold days, and on those days the spillage seemed less. This is when I started considering extending my chimney.

I also think the offset box contributes to my problem.


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## oldspark (Oct 11, 2013)

dafattkidd said:


> Thanks for that. Where is that from?


 http://firewood.com/index.cfm/pageid/28


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## Jags (Oct 11, 2013)

Temps sound good.  Back to staring down the chimney.


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## mellow (Oct 11, 2013)

You need more draft to compensate for that offset box,  a 90 in a chimney takes off 5 feet in overall length,  so I would guess an offset box takes off 8 feet.


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## oldspark (Oct 11, 2013)

This is good info also.
http://woodheat.org/how-chimneys-work.html


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## Sprinter (Oct 11, 2013)

dafattkidd said:


> I would honestly prefer the fan over the extended height. The extra pipe coming out of my chimney will look ridiculous. I am almost positive I have read Begreen express serious reservations about draft induced fans. Any feedback on the fans?


I know nothing about them but they seem to be very expensive.  http://www.northlineexpress.com/fir...ducers/enervex-chimney-fan-rs-012-rs-012.html


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## brenndatomu (Oct 11, 2013)

Sorry, maybe this was already covered elsewhere, but I'm assuming you have a masonry chimney with SS liner? Is it insulated? That would add some draft if it was.
As to one of your original questions, how to extend your chimney height, again, assuming masonry chimney with a SS liner. They make a top plate that adapts from flex liner to class A pipe. I know I have seen a link to one here somewhere before, maybe someone else can put their finger on it more quickly than I.
I have no experience with those draft inducer fans, but to me, that looks like a real PITA on a wood burner chimney...


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## Woody Stover (Oct 11, 2013)

dafattkidd said:


> I have insulation at the top foot and bottom foot of an interior chimney.


So you don't have a full-length stainless liner?

_"The chimney must have an acceptable 6" (152 mm) stainless steel chimney liner installed."
"The 2400 Insert is not approved for use with a positive flue connector into a masonry flue."
_
Terminology differs, but what they are calling a 'positive connection' is what I call a 'direct connection,' where the stove connector pipe goes up through a block-off plate, then uses the masonry chimney clay liner tile the rest of the way up. They are saying this is a no-no. I call a liner all the way up, a 'positive connection.'


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## dafattkidd (Oct 11, 2013)

I have a 6" liner running from an offset box which is directly connected to my stove. The liner goes up to the cap. Only the lower and upper portions of the liner are insulated.


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## mellow (Oct 11, 2013)

He has a liner,  he just put insulation at the top and bottom instead of the whole thing.


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## Woody Stover (Oct 11, 2013)

The manual is confusing, because below that in section 1.2 it says you _can_ use a masonry chimney.... 

http://www.osburnwoodstoves.com/v/vspfiles/files/2400 insert.pdf


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## Woody Stover (Oct 11, 2013)

dafattkidd said:


> I have a 6" flex liner running from an offset box which is directly connected to my stove. The liner goes up to the cap. Only the lower and upper portions of the liner are insulated.


OK, gotcha.


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## oldspark (Oct 11, 2013)

If it is a inside chimney (I think he said it was) the insulation is less of a factor.


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## Woody Stover (Oct 11, 2013)

I don't see an actual minimum flue height figure listed....


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## oldspark (Oct 11, 2013)

Woody Stover said:


> The manual is confusing, because below that in section 1.2 it says you _can_ use a masonry chimney....
> 
> http://www.osburnwoodstoves.com/v/vspfiles/files/2400 insert.pdf


 
nothing wrong with a masonry chimney if built correctly


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## brenndatomu (Oct 11, 2013)

oldspark said:


> nothing wrong with a masonry chimney if built correctly



And flue sized correctly for the stove...

Insulation at the top and bottom only? That is kind of an interesting install, no?


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## Woody Stover (Oct 11, 2013)

I gotta believe that the offset box is the culprit here.


dafattkidd said:


> Just 6" galvanized chimney like on an oil burner?


You can get the cheap snap-together black stove pipe at a farm store.



oldspark said:


> nothing wrong with a masonry chimney if built correctly


You won't get as much draft as with a liner, but that's not the issue here.


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## begreen (Oct 11, 2013)

dafattkidd said:


> Just 6" galvanized chimney like on an oil burner? Will that really give me a pretty accurate idea of the effects?


Yes, grab a 3 or 4' length of 6" galv. lightweight venting duct, remove the cap and temporarily put it in crimp down. Secure so that it doesn't fall down and light the fire.


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## oldspark (Oct 11, 2013)

Woody Stover said:


> I gotta believe that the offset box is the culprit here.
> You can get the cheap snap-together black stove pipe at a farm store.
> 
> You won't get as much draft as with a liner, but that's not the issue here.


 
A correctly built chimney has a clay liner in it.


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## Woody Stover (Oct 11, 2013)

oldspark said:


> A correctly built chimney has a clay liner in it.


True, but the clay liner is going to have a larger cross-section area, slowing the draft. And according to your previous post, dropping the flue gas temp will slow draft. So an _insulated_ liner will definitely draft better than the clay....


oldspark said:


> Most draft problems have to do with inadequate gas temperature in the chimney"


I don't know if he's got enough room in the clay liner to insulate his stainless liner, but that would have to help. I'm not sure how _much_ it would help, though.


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## Bluerubi (Oct 11, 2013)

oldspark said:


> Do you have a link to that product, sounds interesting.



I don't think what I have now is anything too special, just completely open.  http://www.woodlanddirect.com/Chimney/Multi-Flue-Chimney-Caps/Stainless-Chimney-Champion-Flat-Lid

The old one was fine, just had some restriction due to the slot design around the small diameter cap.  With a wide open liner I am certain my draft has gone up dramatically.


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## oldspark (Oct 11, 2013)

Inside chimney so insulation may not be that big a deal.
Chimney is on the short side a little height may be the most bang for the buck.


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## oldspark (Oct 11, 2013)

Woody Stover said:


> True, but the clay liner is going to have a larger cross-section area, slowing the draft. And according to your previous post, dropping the flue gas temp will slow draft. So an _insulated_ liner will definitely draft better than the clay....
> I don't know if he's got enough room in the clay liner to insulate his stainless liner, but that would have to help. I'm not sure how _much_ it would help, though.


 Getting side tracked here, they used to make a 7 and1/4 round clay liner and yu can go 25% larger with the liner size.


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## oldspark (Oct 11, 2013)

Bluerubi said:


> I don't think what I have now is anything too special, just completely open.  http://www.woodlanddirect.com/Chimney/Multi-Flue-Chimney-Caps/Stainless-Chimney-Champion-Flat-Lid
> 
> The old one was fine, just had some restriction due to the slot design around the small diameter cap.  With a wide open liner I am certain my draft has gone up dramatically.


 
Those are nice, many people have reported their chimney caps are too restrictive.


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## dafattkidd (Oct 12, 2013)

So what if this does work?  How do I connect a 4 foot section of Class A to a liner?


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## Oregon aloha (Oct 12, 2013)

I thought all EPA stoves have a 15' min. height because that is the EPA testing height. Is this not true?


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## brenndatomu (Oct 12, 2013)

See post 32, line 5...EDIT, I'll pull it back up, see next post.


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## brenndatomu (Oct 12, 2013)

brenndatomu said:


> Sorry, maybe this was already covered elsewhere, but I'm assuming you have a masonry chimney with SS liner? Is it insulated? That would add some draft if it was.
> As to one of your original questions, how to extend your chimney height, again, assuming masonry chimney with a SS liner. _*They make a top plate that adapts from flex liner to class A pipe.*_ I know I have seen a link to one here somewhere before, maybe someone else can put their finger on it more quickly than I.
> I have no experience with those draft inducer fans, but to me, that looks like a real PITA on a wood burner chimney...



Lemme see if I can find a link for ya...EDIT, here's one example
http://www.olympiachimney.com/products/cat/VCAA/VCATSAP/VA_TP0


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## dafattkidd (Oct 12, 2013)

brenndatomu said:


> Lemme see if I can find a link for ya...EDIT, here's one example
> http://www.olympiachimney.com/products/cat/VCAA/VCATSAP/VA_TP0


 
Perfect. Thanks. Unfortunately (or fortunately) it has been too warm for burning. I will pick up a piece of four foot galvanized and have it ready for the test burns. If this doesn't work are the draft inducing fans a viable safe option?


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## STIHLY DAN (Oct 12, 2013)

Your chimney may be the problem, Have you looked into the house being in a negative pressure? Exhaust fans, combustion air, dryer. Try opening a window when you open the door to the stove. Also why would you have smoke at all when reloading a burnt down fire? Is your wood actually dry?


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## Woody Stover (Oct 12, 2013)

Oregon aloha said:


> I thought all EPA stoves have a 15' min. height because that is the EPA testing height. Is this not true?


The Keystone manual says 14' but that's with a 7" flue. I'm running 6" at 17'....drafts great.
The Hearthstone Manchester says 10'....from the floor!


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## Sprinter (Oct 12, 2013)

Woody Stover said:


> The Keystone manual says 14' but that's with a 7" flue. I'm running 6" at 17'....drafts great.
> The Hearthstone Manchester says 10'....from the floor!


Yeah, I think that's just a suggested minimum, and probably a good rule of thumb, but mine is only 13' and drafts okay (not great, but okay).  Some stoves seem to "breathe" better than others.


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## begreen (Oct 12, 2013)

Some stoves definitely breath easier than others. Cat stoves that don't rely on secondary air can often get along with a bit less chimney than secondary burners. The design of the secondary intake manifold plays a major part. If it is narrow and/or has a long path with 90 degree turns then it is going to require stronger draft to work well. That is my theory as to why the PE stoves breath easier. They have a large rectangular secondary tube in the back that goes straight up into the large baffle plenum. That is much less restrictive than a stove which has a longer secondary manifold with a couple right angle turns and say a 1" tube intake. 

That should not fault a good secondary burner. With a decent height chimney they can perform very well. Case in point would be the Englander 30NC which is an exceptionally clean burning stove.


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## dafattkidd (Oct 12, 2013)

STIHLY DAN said:


> Your chimney may be the problem, Have you looked into the house being in a negative pressure? Exhaust fans, combustion air, dryer. Try opening a window when you open the door to the stove. Also why would you have smoke at all when reloading a burnt down fire? Is your wood actually dry?


 
My wood is ok. That's not the issue. My house is pretty drafty so I doubt that it's negative pressure. In fact I've tried loading with a window open and no help. I'm pretty positive it's the chimney height or the offset box, or both.


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## Dustin (Oct 13, 2013)

What type of stove? I get smoke spillage each and every time I open the door to my quad. No matter what I do.

25 feet of flex on an interior chimney. Some stoves like putting a little smoke in the room I think


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## dafattkidd (Oct 13, 2013)

Dustin said:


> What type of stove? I get smoke spillage each and every time I open the door to my quad. No matter what I do.
> 
> 25 feet of flex on an interior chimney. Some stoves like putting a little smoke in the room I think


 
I have an Osburn 2400 insert. It's a basic unit. No bells and whistles just a beast. There are other members on the forum with the same unit who do not share this experience. It's not the stove. It's the chimney system.


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## Sprinter (Oct 13, 2013)

dafattkidd said:


> Here's my version of the math: 12 ft chimney + 3 ft (25%) increases draft by 25%. Is this correct?


I believe the math is right.  I've read other sources that confirm that kind of relationship.   So if you go ahead and add 3 ft, you probably will get about 25% more draft which more than likely will solve your problem.  Every additional increase in height, though, will have a lesser affect.

Do what others have suggested and temporarily add some cheap stovepipe.  That will tell the tale.


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## BCC_Burner (Oct 13, 2013)

I think adding height is the best option here.  Also, don't overlook the basics to help improve things a bit before you add height.  Open the primary air all the way for 30-60 seconds before opening the door, and open the door slowly.  I usually leave mine cracked open just slightly for a couple seconds before slowly opening it the rest of the way.  Being vigilant about those two steps really reduced smoke spillage in my experience.


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## begreen (Oct 13, 2013)

Dustin said:


> What type of stove? I get smoke spillage each and every time I open the door to my quad. No matter what I do.
> 
> 25 feet of flex on an interior chimney. Some stoves like putting a little smoke in the room I think



Something doesn't sound right there. Did the liner get flattened a lot to pass thru the damper? Is the baffle all the way to the rear of the stove? Has the baffle been checked to see if there is a mound of soot sitting directly under the flue collar? Is the cap screen clean?


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## oldspark (Oct 13, 2013)

Yea 25 feet of chimney should not spill smoke back into the room, I only have 18 feet and it never spills back into the room and it did not with the old chimney and old stove.


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## Charles1981 (Oct 13, 2013)

I have a 27 foot 6 inch chimney. My masonry chimney is completely interior in the middle of the home in the basement. I have 6 inch SS pipe all the way up (my installer said because I have a interior, clay lined masonry chimney  I had no need for insulated double walled pipe. 

I have it hooked up to a encore 2 in 1. 

From some other posts drafts have been a significant issue for people with this stove. I am wondering if because of the height, location, and diameter of chimney/liner this is one reason the stove has been performing as it supposed to? Seems like i have an ideal situation for any stove...unless there was a problem with too much draft...but I'm not sure how to tell if I have too much draft?


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## dafattkidd (Dec 11, 2013)

So for the past two weeks I have been running the unit with a four foot piece of single wall stove pipe attached to the top of my liner.  The additional four feet has slightly improved my smoke in your face problem, but not really fixed it.  It has to be the offset box.  I have a mason coming to my house today to tell me if I can make some adjustments to the masonry to eliminate the offset box. 

I do however like the way my stove runs with the longer chimney.  It seems to take off faster, I can pack the splits tighter and have a more complete burn.  It looks RIDICULOUS though.  Holy cow it looks terrible.  I'll post a picture just for kicks. 

I'll update the thread after speaking to the mason today.  For the record: The mason who is meeting me at my house today has done a ton of work for my company (we build very high end homes in the Hamptons).  So his opinion holds a lot of weight in my book.


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## dafattkidd (Dec 11, 2013)

Ok. Bad news.  There are some options, but they are pretty invasive and expensive. My last hope is this:  The fireplace has a steel box with vents that was most likely installed in the 70s or early 80s.  Based on the measurements it looks like behind this steel box is a full masonry fireplace.  The only way to tell is to cut out the steel.  If I do this, I can slip my insert further back into the fireplace eliminating the need for an off set box.  I think the steel is most likely too think to cut with a sawzall.  We think we probably need to hit it with a plasma cutter.  

Can anyone confirm that the steel boxes installed in the 70s and early 80s were too thick to be cut with a sawzall?


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## Jags (Dec 12, 2013)

I have cut 1/4" plate with a sawsall.  Goes faster than you think.


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## MDFisherman (Dec 12, 2013)

Or a angle grinder with a cutting wheel will make short work of that for sure.


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## dafattkidd (Dec 12, 2013)

Good to hear. 

*The plan would be:* Disconnect the liner from the insert.  Slide insert out of fireplace. Cut the steel box out.  Pray that it is fully masonry behind that. Slide my insert deeper into pocket of the fireplace so the exhaust passes the lintel. Directly connect the liner to the insert.  Light a massive fire with no smoke spillage, and drink a beer.

*Most likely the actual outcome:* Attempt to disconnect liner from insert, but the tight squeeze between the top of the insert and the lintel lead me to have to sawzall the God forsaken off set box.  Pullout insert and damage my hearth.  Begin to attempt to sawzall steel box. Break/destroy several sawzall blades.  Run out buy ore sawzall blades.  Burn out sawzall.  Engage in raging break down.  Run to nearest fireplace supplier purchase offset box.  Connect offset box to liner.  Slide insert back into place, connecting offset box as the I shimmy the insert back into place.  Light fire.  Get face full of smoke.  Drink beer.  Nod head repeatedly in disappointment.  Post results on Hearth.com


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## Jags (Dec 12, 2013)

You are quite the optimist.  I would expect the outcome to be much worse.


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## brenndatomu (Dec 12, 2013)

keepin it real this morning...


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## mellow (Dec 12, 2013)

Mine had another steel back behind the steel back that you are cutting out to allow the heat to move behind it for the heatilator vents.


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## oconnor (Dec 12, 2013)

Instead of cutting the entire fireplace out, can you just cut the fireplace throat so you can get a better angle to the liner?


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## ohlongarm (Dec 12, 2013)

dafattkidd said:


> Hey,
> 
> Admittedly my install is not bulletproof.  I have about 14 feet from the bottom of my unit to the top of my chimney so probably like 12" of actual chimney liner.  My insert heats fantastically, efficiently and burns cleanly. I try to burn good dry wood as best as I can.
> 
> ...


 I had 12 feet for my BK Ultra the minimum required,this fall I added 4 more now at 16 incredible increase in efficiency 12 to 18 hours in sub zero wind chills with house at 73* and stovetop always at 500 to 550 minimum,PS my wood is primo nothing less than 3 years.To answer your question you are correct an increase of 3 increases a 12 foot run by 25%.


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## oconnor (Dec 12, 2013)

It occurs to me that 14 feet with an offset box is essentially a 9 foot flue. The rule of thumb for direction changes is a flue is a loss of five feet for each 90 degree bend.


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## oldspark (Dec 12, 2013)

oconnor said:


> It occurs to me that 14 feet with an offset box is essentially a 9 foot flue. The rule of thumb for direction changes is a flue is a loss of five feet for each 90 degree bend.


 
That sounds good but with two stoves and two chimneys going from removing 2 90's to straight up  the difference was marginal I question those figures.


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## brenndatomu (Dec 12, 2013)

Yeah, 5 ft. sounds a lil strong. I've always heard it was more like 3-4 ft. per 90.


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## oldspark (Dec 12, 2013)

brenndatomu said:


> Yeah, 5 ft. sounds a lil strong. I've always heard it was more like 3-4 ft. per 90.


 
I even question the 3 to 4 feet, if I had to guess with my real world expeirence it would be 1 to 2 feet, I removed 2 90's and it make a slight difference.
Of course it depends on how crappy the draft is in the first place.


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## dafattkidd (Dec 12, 2013)

Ok. I spoke with a chimney guy I work with. It's probably a bad idea to cut out that steel box. He said there's a good chance it will make my fireplace be out of code and probably void my homeowners insurance.

I think the only options are: 1 get a different insert with an exhaust system that is more suitable for my insert. 2 install an exhaust fan at the top of my chimney. Crap!

I'll probably opt for 2 as he offered to give it to me at cost saving me $700. Honestly, I'm probably not going to do much about this any time soon.


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## oconnor (Dec 12, 2013)

brenndatomu said:


> Yeah, 5 ft. sounds a lil strong. I've always heard it was more like 3-4 ft. per 90.



Regardless of 2 or 5 feet per 90, the offset box is two 90* turns, so between 4-10 feet of effective chimney height reduced. He only has 12 feet to start with, so it's not going to work well, and as the OP has stated isn't.


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## oconnor (Dec 12, 2013)

dafattkidd said:


> Ok. I spoke with a chimney guy I work with. It's probably a bad idea to cut out that steel box. He said there's a good chance it will make my fireplace be out of code and probably void my homeowners insurance.
> 
> I think the only options are: 1 get a different insert with an exhaust system that is more suitable for my insert. 2 install an exhaust fan at the top of my chimney. Crap!
> 
> I'll probably opt for 2 as he offered to give it to me at cost saving me $700. Honestly, I'm probably not going to do much about this any time soon.



What did he say about modifying the throat of the fireplace to take the offset box out of the equation? Seems to me it's done fairly regularly.


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## mellow (Dec 12, 2013)

I would double check to see what code it would void,  I would try to find something in writing before discounting that.  If it is clearance to combustibles and we are talking about a ZC insert I would understand but pure masonry it shouldn't be an issue.


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## oldspark (Dec 12, 2013)

oconnor said:


> Regardless of 2 or 5 feet per 90, the offset box is two 90* turns, so between 4-10 feet of effective chimney height reduced. He only has 12 feet to start with, so it's not going to work well, and as the OP has stated isn't.


 
Just saying losing the 2 90's might not make it into a hoover, the 12 feet is probably the issue.


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## dafattkidd (Dec 12, 2013)

oconnor said:


> What did he say about modifying the throat of the fireplace to take the offset box out of the equation? Seems to me it's done fairly regularly.



The problem is the lintel sits directly above the exhaust of the stove.  I'm not sure I follow how modifying the throat of the fireplace would help. Can you further explain how you think this would help?  Thanks.


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## dafattkidd (Dec 12, 2013)

oldspark said:


> Just saying losing the 2 90's might not make it into a hoover, the 12 feet is probably the issue.



Even with the added 4 foot of stove pipe it was little improvement.  I'm pretty convinced it's the offset box.  16 foot interior chimney should draft pretty well.  Do you have any suggestions? I'm thinking my only option is a very expensive exhaust fan.


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## oconnor (Dec 12, 2013)

dafattkidd said:


> The problem is the lintel sits directly above the exhaust of the stove.  I'm not sure I follow how modifying the throat of the fireplace would help. Can you further explain how you think this would help?  Thanks.



Sometimes by cutting away some of the metal associated with the original damper you can make more room for the liner to connect to the stove. You need to pay attention to clearances, but usually there is only the masonry of the fireplace nearby. You can wrap the liner with ceramic fibre blanket to keep heat from radiating thru masonry to any combustibles.


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## brenndatomu (Dec 12, 2013)

oconnor said:


> Sometimes by cutting away some of the metal associated with the original damper you can make more room for the liner to connect to the stove. You need to pay attention to clearances, but usually there is only the masonry of the fireplace nearby. You can wrap the liner with ceramic fibre blanket to keep heat from radiating thru masonry to any combustibles.


^^^ This and a 15 degree stainless elbow could give you some flexibility?


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## dafattkidd (Dec 12, 2013)

brenndatomu said:


> ^^^ This and a 15 degree stainless elbow could give you some flexibility?


 
Nope. I have 2 3/8" from the top of the insert to the lintel and the lintel is directly over the exhaust of the insert.


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## oconnor (Dec 12, 2013)

Could a custom fab offset box be made that would give more flow? Have it made from 316 stainless.


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## dafattkidd (Dec 12, 2013)

oconnor said:


> Could a custom fab offset box be made that would give more flow? Have it made from 316 stainless.


 I was thinking the same thing. It may be a slight improvement. I'll see. I have a buddy who has a decent set up. We could possibly fabricate something, but I still think ultimately I will need an exhaust fan.


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## Oregon aloha (Dec 13, 2013)

What if you used one of those chimney caps they use in high wind areas that are closed on one side and rotate with the wind.. They improve draft even when there is no wind.


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