# Odd "Chemical/Acidic" Smell from Wood Burner



## PreFab (Feb 11, 2013)

Hello.
I'm dying for an answer on this one.  I have a prefab wood burner that starts to emit a very odd "chemical/acidic" smell (can't think of any other way to describe it) after burning regular hardwoods for about an hour or so.  Even weirder is that I noticed it happens faster after I've cleaned all the ash out.  If I don't clean out the ash but instead slide the ash off to the sides to allow the embers to breath directly beneath the grate...it doesn't start to smell for hours and the smell doesn't seem to ever get that strong.  But if I have cleaned out the ash completely...it smells within an hour and the smell starts to get bad enough that I have to let the fire die and open a window. 

Some other details:
** PreFab unit was installed when home was built in mid-80's.

** The unit was converted to gas logs prior to me moving in.  I ended up pulling the gas line and logs this year and had a chimney sweep come in and verify all looked good and he cleaned the chimney and box but said it was pretty close to immaculate.  He mentioned he didn't need to come back until after 1 to 2 cords of wood were burned which I'm at maybe about a 1/2 of cord.

** I could see through the top and bottom vents lots of dust which I thought might be the cause.  I took the vents off and diligently cleaned the dust and "sticky" tar like build up on the metal exterior surface on top of box and on bottom.

** I don't see any signs of paint or anything that would be causing it.

** There was a small amount of "caulk" used to fill the 1/2" hole in the very back bottom left corner in the refractory panel where the gas line came in.  I thought the caulk might be the cause but after this much time it seems odd it would still smell.  I also packed a bunch of ash to cover up just where the caulk is and cleaned out the rest just to see if the smell was delayed like I mentioned above but it didn't.  It started to smell just as if I had cleaned the whole thing out.

So that's all I got.  I know it's a lot but I'm just so frustrated and would die for an answer!  I can post photos too if that would help.  I love burning wood so this problem is SO disappointing.

Thanks!!  -- Patrick


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## fox9988 (Feb 11, 2013)

The tar like substance sounds like creosote. If you have creosote leaking out of the firebox, you have a Very dangerous fire hazard. Picture a flue fire on the surface of your stove. The ash may be insulating the bottom of the firebox keeping the creosote from getting hot enough to stink. To me, hot creosote has a burnt popcorn-burnt bean smell + a chemical odor. When you cleaned it, did the tar have the same odor you smell during burning?
Hopefully the "caulk" is furnace cement.


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## PreFab (Feb 11, 2013)

fox9988 said:


> The tar like substance sounds like creosote. If you have creosote leaking out of the firebox, you have a Very dangerous fire hazard. Picture a flue fire on the surface of your stove. The ash may be insulating the bottom of the firebox keeping the creosote from getting hot enough to stink. To me, hot creosote has a burnt popcorn-burnt bean smell + a chemical odor. When you cleaned it, did the tar have the same odor you smell during burning?
> Hopefully the "caulk" is furnace cement.


 


Yeah, I guess the smell could be like burnt popcorn/burnt bean.  That's a tough one as the chemical smell seems to dominate for me.   The tar I cleaned up did sort of have the same type of smell.  It was like a very thin even coating along the entire top metal surface of the box as well as the underside of the box.  Those were really the only places I could reach... the top and the bottom.  But the air space between the box and the foil insulation looked really clean.  Also the "caulk" was put in by the chimney sweep and ensured me it was meant for filling cracks in fireplaces so I really hope it was the right stuff.  I can't say for sure though.

I have a fire burning right now and the smell is here.  If I stick my nose close to the bottom vent... no smell at all.  If I stick my nose close to the top vent...the smell is very strong.  It seems to roll out with the heat that rolls out of that top vent.

There doesn't appear to be smoke leaking out of the box... so how does a firebox get creosote leaking out of it?  I don't get how it would coat the top and bottom surface of the sheet metal of the box??


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## PreFab (Feb 11, 2013)

Here is the front view of the fire place...


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## Gark (Feb 11, 2013)

What is your flue setup? For chimney pipe vertical runs, the bottom of each section of pipe must fit inside of the section below it. The top section is male, that below it is female at each union. This is so any creosote running down inside  the flue pipes stays contained inside the pipe. Perhaps one of your unions is bass-ackwards, letting creosote  leak on your firebox. Did your sweep check for that? Burning gas (logs) would not reveal such a reversed union, because gas doesn't make creosote.


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## PreFab (Feb 11, 2013)

Here is the close up of the top vent.  You'll see the shiny aluminum chimney vent (or whatever it's officially called) called on the right.  You'll also see a thin piece of sheet metal lifted about 2 to 3 inches above the firebox.  I needed to clean this as well as it too had the thin coat of "tar".  And the foil insulating around the outside of the box can sort of be seen...


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## PreFab (Feb 11, 2013)

Here is a close up of the bottom vent.  Again you can see the foil insulation in the back.  Also it too has a piece of sheet metal that is connected to the bottom of the firebox...almost like a hanging bridge.  It needed to be cleaned on the top side as well.  I have no idea how something would have leaked on it as it's completely under the bottom of the box...


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## PreFab (Feb 11, 2013)

Gark said:


> What is your flue setup? For chimney pipe vertical runs, the bottom of each section of pipe must fit inside of the section below it. The top section is male, that below it is female at each union. This is so any creosote running down inside the flue pipes stays contained inside the pipe. Perhaps one of your unions is bass-ackwards, letting creosote leak on your firebox. Did your sweep check for that? Burning gas (logs) would not reveal such a reversed union, because gas doesn't make creosote.


 

I see what you mean.  That makes sense.  Would I be able to see this or would the chimney sweep be able to tell?


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## Gark (Feb 11, 2013)

I gotta agree with the previous response that possible creosote, a flammable (carcinogen?) On the human side of the firebox is dangerous. I wouldn't burn again until the issue is resolved. The chimney service we had visit here did have a camera to inspect the flue, but I don't know if they could see a reversed union. Maybe with a cold stove they would just dribble some colored water down the inside surfaces of the flue pipe to see if the water ended up inside the stove or on top of it.


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## fox9988 (Feb 11, 2013)

Thin even coating doesn't sound like creosote leaking. The firebox looks fairly clean. Burnt popcorn/beans may not be a good description, a very chemical smell (fumes?).
Do you get the smell when the fan is off?


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## Gark (Feb 12, 2013)

Do you have a chimney cap on top of your flue pipe?


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## PreFab (Feb 12, 2013)

Thanks for your responses on this so far!

@fox9988 -- there is no fan.

@Gark -- yes, there is a chimney cap on top of the flue pipe.  And now that you mention that... it had an exterior rust you could see so about 3 years ago I had the chimney company look into replacing it but it was not a standard cap and was alot of money for a stainless steel replacement.  So after he told me it was structurally in good condition, he suggested to just wire brush the exterior rust off and paint it black which he did.  Still looks like it's holding up good today.

Couple of questions/thoughts -->

* Any chance the paint on the cap is smelling and somehow drafting down the flu when I'm burning?  Seems hard to believe but what do I know.

* What do you all think makes sense... should I schedule another visit with the chimney guy but this time have the fire burning so he can smell the smell first hand?  Then maybe he could come back again after taking note of it with no fire going to check things out?  Is that crazy?

* I'm still struggling with understanding how the cresote would get on the bottom of the fire box.  The same stuff I cleaned from the top was on the top surface of that bridge piece thats attached to the underside of the bottom of the box.  If you saw it, you'd see it's almost impossible for something to get to that surface from the top of the flu pipe.  Could it be years of dust that literally melts and causes a thin coat of smelly "tar"?  Either way...I'll definitely run the theory by the chimney guy to verify the vertical flu pieces were connected correctly to not allow leaks to the outside surface of the flu.


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## Backwoods Savage (Feb 12, 2013)

Creosote will get all over and it does stink bad. If you have it in the stove, you also have it in the chimney and probably worse there.

Big question is the fuel. Can you describe what you are burning? When was this wood cut? When was it split? How long has it dried since being split? Did you put this wood up yourself or did you buy it?


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## PreFab (Feb 12, 2013)

Backwoods Savage said:


> Creosote will get all over and it does stink bad. If you have it in the stove, you also have it in the chimney and probably worse there.
> 
> Big question is the fuel. Can you describe what you are burning? When was this wood cut? When was it split? How long has it dried since being split? Did you put this wood up yourself or did you buy it?


 
Had a cord of split seasoned hardwood delivered and thats what I'm making my way through.  It's mixed oak, cherry, maple, ash, and looks like some poplar as well. I wouldn't know exact dates as it was delivered. I did end up splitting most of it again so I didn't have such large pieces. It seems to burn great... good loud pops and not overly smokey.


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## Backwoods Savage (Feb 12, 2013)

What is "seasoned" firewood?

The fact that you bought the wood tells us that the wood is not as dry as it should be. They usually split the wood just before delivery and sometimes even cut it to length just before delivery. That is not dry.

Splitting it again will help it dry faster for sure....if you stack it out in the wind. If you ever get hold of some good dry wood, wood that has been split and stacked for 3 years or more, you will be amazed. One of the best parts of this will also be that you get more heat from less wood burned. You also won't get creosote.


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## ohlongarm (Feb 12, 2013)

PreFab said:


> Hello.
> I'm dying for an answer on this one. I have a prefab wood burner that starts to emit a very odd "chemical/acidic" smell (can't think of any other way to describe it) after burning regular hardwoods for about an hour or so. Even weirder is that I noticed it happens faster after I've cleaned all the ash out. If I don't clean out the ash but instead slide the ash off to the sides to allow the embers to breath directly beneath the grate...it doesn't start to smell for hours and the smell doesn't seem to ever get that strong. But if I have cleaned out the ash completely...it smells within an hour and the smell starts to get bad enough that I have to let the fire die and open a window.
> 
> Some other details:
> ...


I don't know if this helps but I had the same thing a few weeks ago,smelled like plastic burning with an odd chemical smell. What it turned out to be was the underside of the chimney cap caught on fire when it burned itself clean the smell went away.The next day I cleaned the cap it had crusty creosote in it,funny thing though the chimney was spotless,look forward to anyone else's input.


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## PreFab (Feb 13, 2013)

ohlongarm said:


> I don't know if this helps but I had the same thing a few weeks ago,smelled like plastic burning with an odd chemical smell. What it turned out to be was the underside of the chimney cap caught on fire when it burned itself clean the smell went away.The next day I cleaned the cap it had crusty creosote in it,funny thing though the chimney was spotless,look forward to anyone else's input.


 
Hmmm... interesting.  So the smell did travel all the way down from the cap.  I'll definitely have that checked.  Thanks!


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