# Why does smoke sink?



## Tinstaafl (Jan 6, 2008)

Wondering if any of you chimney guys have ever looked into a situation like this.

3-4 years ago, my neighbor tore down the existing house and built a new one. The chimney is 25-30' tall built to code, and draws nicely for his basement woodburner. However, under almost all weather conditions, the smoke exits the top and immediately curls downward. In less than one heating season, the top 5' of the chimney was completely black.

Last fall, he added a several foot tall metal extension, but the smoke still falls immediately. The chimney on the old house didn't behave that way, nor do any of the neighbors'.

Barometric pressure doesn't seem to have much effect at all. The only factor I can think of that's significantly different from when the old house was there is that he has cut down a large percentage of the trees on his lot (we're in an oak forest on a mountainside).


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## superseal (Feb 4, 2009)

quite possible prevailing winds and new house design (roof) may be aiding in this downdraft. Any pics?


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## JBM (Mar 31, 2011)

What size is the flue?


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## MAULEMALL (May 16, 2010)

It has an inadaquit draft.. And if it is black tell him to look down into his flue and see if the joints are still between the tiles..

Get some pics man ...PICS... :laughing:


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## NYCB (Sep 20, 2010)

Does he get smoke when he opens the door to his burner?

Seems like a flue size issue or temperature problem.

Mine will do that also when the fire isn't hot enough or if it is humid out. My chimney goes through the basement wall and up the outside of the house.

My dads chimney goes straight up through the house and out he roof and he never has issues with his, smoke always goes straight up. I believe mine is more susceptible to cooling before exiting the top.


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## dakzaag (Jan 6, 2009)

Tinstaafl said:


> The only factor I can think of that's significantly different from when the old house was there is that he has cut down a large percentage of the trees on his lot (we're in an oak forest on a mountainside).


Less trees equal more wind. I suspect the flue gasses are just making it out the heated chimney before they cool enough to become heavier than the outside air and immediately drop onto the chimney. If the chimney is on the outside of the house it would experience more windshield temperatures with the new construction than before.

Burn the stove hotter, and or more damper/fresh air to see if he can solve the problem. It could become a decision of more wasted wood vs black soot on the chimney. 

Since he cut all those trees, I supose he saved the wood, which could be different than what he burned in the past. ? Maybe as the wood dries out more it will get better.


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## JBM (Mar 31, 2011)

If the flue is an 8x12 it will not have the same velocity as an 8x8 flue, nor will it be as hot, which in turn provides velocity.


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## Tinstaafl (Jan 6, 2008)

Left my camera at the current jobsite, so all I can do is a crappy phone pic. Prevailing wind is from right to left in the pic, but it happens even when the wind is going 180° opposite.



dakzaag said:


> Less trees equal more wind. I suspect the flue gasses are just making it out the heated chimney before they cool enough to become heavier than the outside air and immediately drop onto the chimney.


I'm thinking you have a point there. Not the wind so much; as I said, it seems to happen in all kinds of weather. But it's a pretty tall chimney on the outside of the house, so the smoke would have time to cool on its way up.

I'm not sure if he's burning slightly green wood or not, but he lived in the old house for a couple of years with the same usage pattern. The 20+ trees he harvested this past year from storm damage, he sold because he was already sitting on plenty of wood.

Don't know the flue size. He claims to have great draft and no smoke issues inside.

He actually doesn't seem too concerned about it, other than the cosmetic issue. It bugs me because I have to look at it. And I live downwind. :laughing:


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## JBM (Mar 31, 2011)

It doesnt look like the chimney was tall enough initially. It needs to be 10 and 2 or it will get down drafts, and the top of the chimney will end up black even


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## Tinstaafl (Jan 6, 2008)

JBM said:


> It doesnt look like the chimney was tall enough initially. It needs to be 10 and 2 or it will get down drafts, and the top of the chimney will end up black even


That's my point, it was tall enough. And now, even with that tin stack on top, the same thing happens.


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## dakzaag (Jan 6, 2009)

Tinstaafl said:


> Don't know the flue size. He claims to have great draft and no smoke issues inside.
> 
> He actually doesn't seem too concerned about it, other than the cosmetic issue. It bugs me because I have to look at it. And I live downwind. :laughing:


Does the HO know your living in his attic...

I would suggest that he try running his fire hotter and observing the change. Once they get in their grove, those wood burners are like a well oiled machine and they run the stove the way they like it. Often it has to do with house temp. Wood supply and getting up at night to feed the fire. Not so concerned about smoke direction and stains.

My guess is it's gonna be black for a long time.:laughing:


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## Morning Wood (Jan 12, 2008)

I thought the top of the chimney is supposed to be 2' above the peak of the roof.


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## jkfox624 (Jun 20, 2009)

Morning Wood said:


> I thought the top of the chimney is supposed to be 2' above the peak of the roof.


If i remember right as long as its 10' leveled in to the roof its fine also.


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## loneframer (Feb 13, 2009)

Morning Wood said:


> I thought the top of the chimney is supposed to be 2' above the peak of the roof.


The rule we always were required to adhere to was 2' above any part of the structure within a 10' level line, or a minimum of 2' above the ridge if it was closer than 10' of the ridge.


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## dom-mas (Nov 26, 2011)

loneframer said:


> The rule we always were required to adhere to was 2' above any part of the structure within a 10' level line, or a minimum of 2' above the ridge if it was closer than 10' of the ridge.


2'11' above the roof line or 2' above a 10' level line in Ontario.

To me it looks like the chimney needs to be higher. It looks just barely high enough with that metal topping. I'm thinking the wind whips over that hollow in the trees, whichever way it's travelling and no matter what speed, takes a dip when it hits the hollow then rises again on the far side. Tree lines are super important when building a chimbley (yeah i know how i spelled it) It's the same as when a tall building is built beside or near an existing. Draft changes dramatically

I can't surmise why it would be worse after he removed more trees except that perhaps before the hollow didn't influence the wind as much as it does now. Oh and there's no way that chimney is approaching 30' high, which is where it should be. it could also be too cold a fire which also promotes creosote and chimney fires. Black cold smoke is no good


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## onthelevel (Apr 6, 2011)

*Chimney is the problem*

Chimney needs to be taller. I always thought the rule was 3' above the ridge of the roof. 
But usually no chimneys are built high enough.
The gasses are probably cooling quickly once they hit the metal extension and then even more from the breeze. 
Had a water heater do that once years ago. Had to go about 4' above the roof the prevent downdraft.

Also if he's burning green wood that could be a big part of it too.


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## JBM (Mar 31, 2011)

The rule is a minimum of 3' over the roofline, 2 feet over the ridge ,or 10 and 2. What this means is that chimneys that come out the center of the peak need to be 3' above the ridge if it is a normal 36" stack, chimneys that are offset should be 2' over the ridge, which in turn makes them naturally more then 3' over the roof. 10 and 2 is you need to go up until you are 10 feet away from the roof, then go 2 feet more


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## superseal (Feb 4, 2009)

yes 2-3-10 rule around here also


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## JBM (Mar 31, 2011)

Every once and a while I will see a squatty little chimney coming out the middle of the peak I lol, duhm arses.


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## dakzaag (Jan 6, 2009)

10-2 is the only rule I have ever heard, but my wife claims I can't hear jack...:whistling

HO has great draft, the chimney is plenty tall to function, whether it meets code or not. (it does appear to be short, but picture angle and distance could be decieving.) The smoke has cooled to the point of just escaping the chimney before dropping. As the fire die's down it is most severe and probably when a majority of the staining occurs. 

If the HO keeps it swept regularly I suspect it will give him many years of service. If I were to purchase the house, I would figure adding height til it meets code and then expect the stains to disappear.

I'm guessing it will remain as is for some time.


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## cdkyle (Jul 12, 2009)

In my past experiences, the chimney always needed to be at least 1' taller than I could reach from that particular scaffold. Almost never failed.:laughing:


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## knucklehead (Mar 2, 2009)

you need more wind


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## griz (Nov 26, 2009)

The 2' more than 10' out is pretty standard.

That chunk of tin pipe needs to be replaced with triple wall flu.

Single wall pipe cools the smoke & chokes the draft.

Also try one of those wind directional flu caps.


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## Tinstaafl (Jan 6, 2008)

dom-mas said:


> To me it looks like the chimney needs to be higher. It looks just barely high enough with that metal topping. I'm thinking the wind whips over that hollow in the trees, whichever way it's travelling and no matter what speed, takes a dip when it hits the hollow then rises again on the far side. Tree lines are super important when building a chimbley (yeah i know how i spelled it) It's the same as when a tall building is built beside or near an existing. Draft changes dramatically
> 
> I can't surmise why it would be worse after he removed more trees except that perhaps before the hollow didn't influence the wind as much as it does now. Oh and there's no way that chimney is approaching 30' high, which is where it should be.


With the metal extension, it's at least 2-3' above the ridge. And even without that, it's 25' if it's an inch--the camera angle is indeed deceiving. That isn't a small house. It's big enough to have a swimming pool in the basement, which it does. :laughing:

As for wind whipping over the hollow, dead calm days are the worst--though that could be related to barometric pressure. Another detail I didn't mention is that the ridge on this house runs roughly 90° off what the old house and those neighboring did/do.

I mentioned the tree harvesting because I do know that while some locations seem to deny the normal laws of physics in terms of chimney behavior, that's the only variable other than a new structure that seems to have any relevance.



dakzaag said:


> HO has great draft, the chimney is plenty tall to function, whether it meets code or not.
> 
> ...
> 
> I'm guessing it will remain as is for some time.


Trust me, it meets code. They're nuts about that around here.

And I agree; you've obviously dealt with wood guys before. :thumbsup: He'll do what he can to have a nice place, but when push comes to shove, practicality will win.


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## Tinstaafl (Jan 6, 2008)

griz said:


> That chunk of tin pipe needs to be replaced with triple wall flu.


Good point, I don't know what it actually is. I suspect he threw it up there just to see if it would solve the problem before going through the expense of extending the masonry. We really don't talk all that much, and I was throwing this question out just from intellectual curiosity more than a real job problem. :thumbsup:


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## lukachuki (Feb 11, 2005)

Tinstaafl said:


> That isn't a small house. It's big enough to have a swimming pool in the basement, which it does. :laughing:


Yowsers!


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## nailkiller1 (Jan 15, 2009)

Most common problem around here is 
The flue or chimney is way to small for the firebox


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