creosote fire or downdraft?

[sarahf]

I have been using my heritage for about 4 weeks now - nearly 24/7. Today, I had been burning a moderate fire (around 250 on the top of the stove) for 4 hours. I put in two logs to get the temp up some, got the fire going (it was up to 350), and smoke started coming back into the house. It was leaking out through the seams in the stove pipe.

I shut the air control down and opened some windows. The smoke stopped coming in right away. I was worried that I had a creosote fire so I took the stove pipe off to clean it. There was between 1/16 to 1/8 inch of black soot and creosote (I guess), most at the seams. There is some of this black stuff down in the firebox (where the stove pipe hooks into the stove at the top). There is also soot/creosote in the chimney (the part that I can see into).

So did I have a creosote fire or was that due to a downdraft? Today was fairly warm (47 or so), rainy, and gusty.

Is the soot/creosote build up too much? Do I need to clean the soot from inside the box??

After reading a bunch of posts, I don't understand this "shoulder" season burning. What should I do when it is 50 outside. I have had a hard time getting the stove up to 350. I have to work hard to get it up there. I get it up to 300-350 2x a day for 30 minutes or so and then let it settle at about 250-280. It keeps the house a great temp because it is warm out. At night I burn it a little hotter (300-325) to last through the night. Is this too low of a stove temp?

I got some oak this year but it wasn't seasoned as much as I thought it should be (about 24% moisture on the fresh interior), so I used a little of it but mostly some dry mixed hardwood. I think that I am starting to get the hang of the fire and can get it hotter, but now I am worried that with all this soot I am doing something wrong (wrong wood, not hot enough fire). I have turned off my stove until I can feel safe about my technique.

Oh, I do get a secondary burn with beautiful blue flames at the top of the stove (up in the baffles).

Thanks for any input.

Missing my nice warm stove,
Sarah

 

[begreen]

Sounds much more like poor draft, not a creosote fire. A crappy split or two may have carboned up things, but from the description it sounds like a lot of soot. Generally in this circumstance you want to do the opposite, open up the air control. Better to burn shorter, hotter fires when the weather is moderate.

 

[sarahf]

So probably not a creosote fire. Would a creosote fire go out right away or would it just keep on going? There was no unusual noise associated with the smoke.

As for small and hot fires, ok. Does that mean get them going and hot (above 350 I guess) and then turn the air down and let the fire go until the house gets cold and start another fire? I had a feeling that I might be at too low of a temp. I hoped the 300-350 burns would burn out any creosote but I guess I need to get hotter. Can't wait to see what the top of the chimney looks like!


Sarah

 

[stoveguy2esw]

BG is correct , better to have shorter hotter fires than a low smouldering one.
here's the physics in basic terms;

stack temperature must be maintained about 212 degrees in order to keep any moisture present (and there will be some present) in its gassious state. if temps drop below water's boiling point you start to condense back into its liquid form. this runs back down the flue and evaporates when it gets closer to the fire and heats up a couple degrees (evaporation is a cooling function, just like when your body sweats to evaporate heat away from your body) this cools the flue more and the cycle can continue weakening draft (which is dependant on a high degree of diference of temperatures between the temp in the stack and the temp outside) a weakened draft may not be able to lift the smoke (which has weight) out the top of the flue. the failure to do this causes the heavier smoke to start to descend as it cools and force smoke coming behind it backwards or out through leaks in the pipe. also the outside temperature being warmer means you need a higher stack temp to make a really solid draft( think about a hot air balloon, it rises due to the air being hotter (and less dense) than the air around it, if the air around it is hot , the air inside must be that much hotter to create rise, and that difference must be also high enough to lift the weight of the balloon itself as well, just like your hot air in the flue must lift the heavier smoke from a low fire)

essentially , you didnt have a flue fire , you would have known , its an ungodly sound, and the pipe would have possibly even started glowing red. i'd say you had downdrafting due to the following factors.

1. a low fire not really heating the flue enough to make a strong enough draft
2. note that outside temps werent severely cold so the differential temp inside the flue was not pronounced as it will be when it gets colder outside.
3. you had smoke leaking out of your pipe joints, if smoke can leak out , air can be sucked in, this air has not been heated by the fire and thus reduces your stack temps as well. before the downdraft started you were likley pulling air into the flue through these leaks, you will want to use a sealer to seal the leaks. this will help your draft as well.

another factor can also contribute , a newer house or one that has been "winterized" by adding new windows, tyvek housewrap and siding all these things contribute to making a house tight , not letting air in (thats the idea right). now think about this , if the house isnt letting air in , then the chimney could struggle to pull the air out as it draws. this is called "negative pressure". outside intake air would be the cure for this.
think about it this way , say you have a bottle of soda, and you are drinking it through a straw, easy right? , its easy because as you suck out the soda, air replaces it right through the neck of the bottle. now , if the bottle had a cork in it and the straw was passed through the cork , you would literally suck the straw flat trying to pull out the soda. because the air cannot come in the bottle to replace the soda. now , if you added a second straw through the cork , then it would be easy to drink again. in this analogy the bottle is the house, and the straw , the chimney. adding an intake solves the problem.

hope this helps ya, this is "chimney 101" as simply as i have learned to explain it.

 

[Bryan53]

Chimney fires from creosote will most likely not be able to be stopped until all the fuel has burned up. The pipe would be roaring. It kinda sounds like a train is coming into your house through the chimney.

 

[begreen]

As for small and hot fires, ok. Does that mean get them going and hot (above 350 I guess) and then turn the air down and let the fire go until the house gets cold and start another fire? I had a feeling that I might be at too low of a temp. I hoped the 300-350 burns would burn out any creosote but I guess I need to get hotter. Can't wait to see what the top of the chimney looks like!

Yes, that is exactly correct. Bring the stove top up to 400 or 500 and then let the fire die out. Then maybe have an evening fire the same way.

 

[sarahf]

3. you had smoke leaking out of your pipe joints, if smoke can leak out , air can be sucked in, this air has not been heated by the fire and thus reduces your stack temps as well. before the downdraft started you were likley pulling air into the flue through these leaks, you will want to use a sealer to seal the leaks. this will help your draft as well.

If I seal around the seams, how do I take the pipe off to clean? This may sound really stupid but I can't get the pipe off the stove without unscrewing some of the pieces. If I seal them how do I get the pipe off? It is double walled.


Another question. My chimney is an outside lined masonry chimney. I know, horrible, but it was there already and brand new! The chimney is somewhere between 25 to 30 feet tall. So, I get that it will be hard to heat a stack that tall but shouldn't the draft be crazy? My house is NOT, I repeat absolutely not well insulated. I don't have the problem of an air tight house. It is nice and old with lots of good fresh air coming in to keep us healthy.

 

[Todd]

Sounds like a draft problem. What is the inside diameter of your chimney? If it's larger than your stove exhaust collar it could be effecting your draft especially it being an outside chimney.

 

[begreen]

Another question. My chimney is an outside lined masonry chimney. I know, horrible, but it was there already and brand new! The chimney is somewhere between 25 to 30 feet tall. So, I get that it will be hard to heat a stack that tall but shouldn't the draft be crazy? My house is NOT, I repeat absolutely not well insulated. I don't have the problem of an air tight house. It is nice and old with lots of good fresh air coming in to keep us healthy.

A cold exterior stack is going to need a lot of heat to keep it warm. You definitely want to keep the stove at warmer temps in order to keep the stack warm too. If this chimney can be enclosed in an insulated chase, I would do that. Otherwise it could be a serious creosote generator.
http://www.woodheat.org/chimneys/evilchim.htm

 

[sarahf]

Another question. My chimney is an outside lined masonry chimney. I know, horrible, but it was there already and brand new! The chimney is somewhere between 25 to 30 feet tall. So, I get that it will be hard to heat a stack that tall but shouldn't the draft be crazy? My house is NOT, I repeat absolutely not well insulated. I don't have the problem of an air tight house. It is nice and old with lots of good fresh air coming in to keep us healthy.

A cold exterior stack is going to need a lot of heat to keep it warm. You definitely want to keep the stove at warmer temps in order to keep the stack warm too. If this chimney can be enclosed in an insulated chase, I would do that. Otherwise it could be a serious creosote generator.
http://www.woodheat.org/chimneys/evilchim.htm

What is the chase? The chimney is a 7-inch square terra cotta and has some sort of cement-like insulation poured between it and the concrete block. Do you mean that I should wrap the outside of the block? Is there something out there to do this yourself?

Thanks

 

[LeonMSPT]

I'll admit a bias toward a stainless liner... higher flu liner temperatures, better draft, cleaner overall.

A problem with terra cotta and brick is, it takes a sustained fire over a few days to heat it up appreciably. Meantime, it's condensing away... forming creosote. Couple that with a small smokepipe coming from an airtight stove... low stack velocity. Junk accumulates.

 

[begreen]

Another question. My chimney is an outside lined masonry chimney. I know, horrible, but it was there already and brand new! The chimney is somewhere between 25 to 30 feet tall. So, I get that it will be hard to heat a stack that tall but shouldn't the draft be crazy? My house is NOT, I repeat absolutely not well insulated. I don't have the problem of an air tight house. It is nice and old with lots of good fresh air coming in to keep us healthy.

A cold exterior stack is going to need a lot of heat to keep it warm. You definitely want to keep the stove at warmer temps in order to keep the stack warm too. If this chimney can be enclosed in an insulated chase, I would do that. Otherwise it could be a serious creosote generator.
http://www.woodheat.org/chimneys/evilchim.htm

What is the chase? The chimney is a 7-inch square terra cotta and has some sort of cement-like insulation poured between it and the concrete block. Do you mean that I should wrap the outside of the block? Is there something out there to do this yourself?

Thanks

This is something generally done by a professional carpenter. The chimney is boxed in a wooden, insulated chase that maintains an air space between the wood and the chimney.

 

[sarahf]

Another question. My chimney is an outside lined masonry chimney. I know, horrible, but it was there already and brand new! The chimney is somewhere between 25 to 30 feet tall. So, I get that it will be hard to heat a stack that tall but shouldn't the draft be crazy? My house is NOT, I repeat absolutely not well insulated. I don't have the problem of an air tight house. It is nice and old with lots of good fresh air coming in to keep us healthy.

A cold exterior stack is going to need a lot of heat to keep it warm. You definitely want to keep the stove at warmer temps in order to keep the stack warm too. If this chimney can be enclosed in an insulated chase, I would do that. Otherwise it could be a serious creosote generator.
http://www.woodheat.org/chimneys/evilchim.htm

What is the chase? The chimney is a 7-inch square terra cotta and has some sort of cement-like insulation poured between it and the concrete block. Do you mean that I should wrap the outside of the block? Is there something out there to do this yourself?

Thanks

This is something generally done by a professional carpenter. The chimney is boxed in a wooden, insulated chase that maintains an air space between the wood and the chimney.

1) The box would be built the whole way up the chimney? I don't think that I have ever seen that but I guess it would look like part of the house anyway. Would that really help or just be a so-so fix that would eventually have to be replaced with a metal chimney?

2) In the mean time. The chimney has a clean-out at the bottom so I can just run the brush up the chimney every couple of weeks. Would that be sufficient?

3) And I have seen a few references to fans that pull the smoke up the chimney from the top. Any thoughts on these? I think that my draft really isn't bad. Smoke has always shot right out of the wood stove and sometimes the match waivers on going out. Just this last time smoke came into the house, but the creosote build up flipped me out.

 

[mtnxtreme]

Another question. My chimney is an outside lined masonry chimney. I know, horrible, but it was there already and brand new! The chimney is somewhere between 25 to 30 feet tall. So, I get that it will be hard to heat a stack that tall but shouldn't the draft be crazy? My house is NOT, I repeat absolutely not well insulated. I don't have the problem of an air tight house. It is nice and old with lots of good fresh air coming in to keep us healthy.

A cold exterior stack is going to need a lot of heat to keep it warm. You definitely want to keep the stove at warmer temps in order to keep the stack warm too. If this chimney can be enclosed in an insulated chase, I would do that. Otherwise it could be a serious creosote generator.
http://www.woodheat.org/chimneys/evilchim.htm

Is this why interior chases are preferred over exterior, does it actually keep the chances of fire or creosote formation down?