Fire inside my Double Wall Stove Pipe?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

rosen431

New Member
Feb 1, 2021
14
Boston, MA
If there is fire in your stove pipe, it means there is fuel in your stove pipe. That should not be there. This means your burning practices may need changing, whether it is the air/damping, or the fuel. Please be safe.

Yeah I think this is the open question.... was it actually a fire in the double wall stove pipe.....?
 
  • Like
Reactions: Highbeam

stoveliker

Minister of Fire
Nov 17, 2019
1,955
Long Island NY
Yeah I think this is the open question.... was it actually a fire in the double wall stove pipe.....?

I wasn't there. But my thoughts are that when you close the damper, you decrease the flow, meaning you also decrease the flux of your transport "vehicle" (gases) with which you move heat into the flue.

Hence a fast increase in temp seems inconsistent with that, but consistent with heat being produced there (that has a hard time leaving its location).

Bottomline, when you don't know for sure what happened, it's safest to assume that the most dangerous thing happened, until you can conclusively rule that out...

It's your home after all...
 

moresnow

Minister of Fire
Jan 13, 2015
1,848
Iowa
Just wondering? I understand you have a long vent but have you run the stove without utilizing the pipe damper? Does it function fine, or does it get uncontrollable? Assuming you added the damper because you needed it? Curious.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,612
South Puget Sound, WA
600F stove top and 500F flue - sounds like you had a pretty good rippin' fire going, then snapped everything closed and the cat lit off?
That is a pretty normal temp for our stove, 3 times a day. Maybe even a little low.
 
  • Like
Reactions: JimBear

rosen431

New Member
Feb 1, 2021
14
Boston, MA
Just wondering? I understand you have a long vent but have you run the stove without utilizing the pipe damper? Does it function fine, or does it get uncontrollable? Assuming you added the damper because you needed it? Curious.

Yeah I've generally run it without the pipe damper most of the time. Right now I'm using 4 year seasoned beech and ash, which has been sitting in my basement for 4 months. So that wood is crazy dry and crazy dense. I filled the ideal steel to the brim with it (twice), and each time it creeped up on me and once it started crossing 675 toward 700 next to the flue collar on the back of the stove top, even with the stove intake air lever all the way closed, I started to get concerned and tried to use the pipe damper more aggressively to slow it down. The pipe damper has not really worked to be honest - it really only seems to be useful in gusty wind conditions. I actually added the damper because the guy that was installing it and Woodstock suggested that with such a long flue I may find I need it and so it makes sense to add it just in case.

Woodstock suggested I "measure the draft" which I assume I do by removing the probe thermometer in the double wall and insert a tube tied in to one of the products linked above. The question quickly becomes... ok, what do I do with that information? Add another pipe damper? Seems like the answer is the same regardless of draft -- i need to put less wood in and have shorter fires. That's annoying, but maybe it just is what it is? I'm pretty frustrated by the whole circumstance to be honest.
 

moresnow

Minister of Fire
Jan 13, 2015
1,848
Iowa
Why are you concerned with a STT of 675-700? Did Woodstock give you lessor operating parameters or?
 

rosen431

New Member
Feb 1, 2021
14
Boston, MA
Why are you concerned with a STT of 675-700? Did Woodstock give you lessor operating parameters or?

Woodstock said 650 max is ideal, except at the front of the stove which routinely gets much hotter because of the combustor. Im not concerned about 675-700, but rather was concerned about a rise far beyond that with no other damper control to utilize, since the stove intake air was fully closed and the STT was continuing to rise through 675 toward 700. My concern was that it would keep going and need further restriction of air beyond the intake air being fully closed. This is why I utilized the pipe damper. It's possible I needed to just leave it alone and all would have been well....
 

moresnow

Minister of Fire
Jan 13, 2015
1,848
Iowa
Woodstock said 650 max is ideal, except at the front of the stove which routinely gets much hotter because of the combustor. Im not concerned about 675-700, but rather was concerned about a rise far beyond that with no other damper control to utilize, since the stove intake air was fully closed and the STT was continuing to rise through 675 toward 700. My concern was that it would keep going and need further restriction of air beyond the intake air being fully closed. This is why I utilized the pipe damper. It's possible I needed to just leave it alone and all would have been well....
Understand. What temp are you supposed to engage the Cat at? Possibly your setup requires a touch earlier engagement and air reduction to keep everything in reason. Dunno! Keep up the info as you go. Thanks
 

rosen431

New Member
Feb 1, 2021
14
Boston, MA
Understand. What temp are you supposed to engage the Cat at? Possibly your setup requires a touch earlier engagement and air reduction to keep everything in reason. Dunno! Keep up the info as you go. Thanks
Woodstock says to engage the cat (close the bypass) right around 300 STT I believe. I engage it right around then. I find that I can't really start turning the air down until STT crosses past 400-450 otherwise there's just not heat and activity in the fire to get it into more of a cat burn with low secondaries which is the goal. I'll keep y'all posted and appreciate the engagement on this! It's super helpful to get other people's thoughts.
 
  • Like
Reactions: moresnow

rosen431

New Member
Feb 1, 2021
14
Boston, MA
Ok - today I disassembled everything and swept the entire flue. Here are some pictures and questions.... my theory at the end of the thread. I very much welcome anyone’s comments on this continuing saga!

first two are the setup in my basement. Double wall stove pipe comes out of the stove, 90 into flue connecting directly to the liner which curves to go straight up to the roof. That first 90 (where you can see the stickers melted off during the incident) is

5BA22A2C-A31F-4FC8-803F-37294FE6D60C.jpeg 6ECFFA65-AC9A-4EF9-B8DF-B7B7960A0C25.jpeg

here’s what I saw when I disconnected for cleaning.

CAD6BA8F-4F8C-49E1-805D-3AC254682DB4.jpeg 0A70F40B-EA5B-4DB0-8723-965FE83E0A3F.jpeg

So clearly a bunch of creosote falling down from the liner. Seems unlikely there was a fire since clearly there’s plenty of fuel right there?

9667EB91-96AD-464E-98E1-FC83ABCCC26C.jpeg
Does this connection between double wall and liner look ok to you guys?
11A45749-6D57-48C4-AEA1-76DD4DFB9EBA.jpeg
There’s a little ding or dent in the liner... anything to worry about ?
BC51837A-96F2-44B0-A40E-BC5D4BC5B67C.jpeg

after sweep

9DD709D5-D65D-43ED-ABE8-623C33766DEE.jpeg
And here is the double wall 90 after I swept it (was a little dirty and sooty.
Should the color change make me nervous / does it mean anything?

DD0F7200-74BE-4C02-87BB-20BD1D0C5925.jpeg
 

gthomas785

Minister of Fire
Feb 8, 2020
530
Central MA
Wait so does your liner do a 90degree bend inside the chimney before it reaches the thimble? That's odd I would have expected a tee in there. Anyway it probably works fine as long as it didn't get crushed on the way in.

The color change means your pipe got hot hot hot.. but shouldn't compromise the integrity of it.

BTW, my pipe is also the same color on the inside

aa26ff754633c9b9f886ef2c354f4f9c.png
 

rosen431

New Member
Feb 1, 2021
14
Boston, MA
Wait so does your liner do a 90degree bend inside the chimney before it reaches the thimble? That's odd I would have expected a tee in there. Anyway it probably works fine as long as it didn't get crushed on the way in.

The color change means your pipe got hot hot hot.. but shouldn't compromise the integrity of it.

BTW, my pipe is also the same color on the inside

View attachment 273878

yeah it basically just makes a 90 degree curve. I guess they could have / should have put a T in, but I’m not sure how they would have accomplished that without doing a bunch of masonry demolition. Does it make a big difference / any difference? Does the connection between the double wall and the liner look ok? Any issues with those dings and dents? And finally -I guess I could replace the 90 double wall, but if it doesn’t matter I won’t. I have been wondering - there are a few screw holes where the pipe never really lined up — maybe air is getting sucked in there? Seems possible but you are talking about a hole covered by another overlapping piece of metal.....
 

gthomas785

Minister of Fire
Feb 8, 2020
530
Central MA
yeah it basically just makes a 90 degree curve. I guess they could have / should have put a T in, but I’m not sure how they would have accomplished that without doing a bunch of masonry demolition. Does it make a big difference / any difference? Does the connection between the double wall and the liner look ok? Any issues with those dings and dents? And finally -I guess I could replace the 90 double wall, but if it doesn’t matter I won’t. I have been wondering - there are a few screw holes where the pipe never really lined up — maybe air is getting sucked in there? Seems possible but you are talking about a hole covered by another overlapping piece of metal.....

When installing the liner you can use one of these tees with the removable snout

1612663502143.png


But if it's not crushed or torn I wouldn't mess with it. And yes it looks fine to me but I'm not a liner expert. The screw holes don't make a difference, especially with double wall.

1612663500022.png
 
Last edited:

ABMax24

Minister of Fire
Sep 18, 2019
1,216
Grande Prairie, Alberta, Canada
Wait so does your liner do a 90degree bend inside the chimney before it reaches the thimble? That's odd I would have expected a tee in there. Anyway it probably works fine as long as it didn't get crushed on the way in.

The color change means your pipe got hot hot hot.. but shouldn't compromise the integrity of it.

BTW, my pipe is also the same color on the inside

View attachment 273878

That chart is way below the operating temp of a chimney. Every double wall I've looked at is rated for at least 1000F continuous operation, mine is good for 1200F continuous, and rated for brief forced firings to 1700F, and tested to 2100F in the event of a chimney fire.
 

gthomas785

Minister of Fire
Feb 8, 2020
530
Central MA
That chart is way below the operating temp of a chimney. Every double wall I've looked at is rated for at least 1000F continuous operation, mine is good for 1200F continuous, and rated for brief forced firings to 1700F, and tested to 2100F in the event of a chimney fire.
That's true, and under normal operating temperatures it is normal for the pipe to become discolored due to the high temperature. However the flue temperature and skin temperature are different things, so when the flue is 1000F, the metal of the pipe may be 500-600.

I imagine the color is affected by more than just temperature. It could also be surface finish, oxygen levels, duration etc. That chart is not from the woodstove industry.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,216
Grande Prairie, Alberta, Canada
That's true, and under normal operating temperatures it is normal for the pipe to become discolored due to the high temperature. However the flue temperature and skin temperature are different things, so when the flue is 1000F, the metal of the pipe may be 500-600.

I imagine the color is affected by more than just temperature. It could also be surface finish, oxygen levels, duration etc. That chart is not from the woodstove industry.

This is double wall, I'm not convinced the skin temp is half that of the flue gas, I think they'd be much closer. Or if he had a chimney fire the flue gas could have been 1200F and the skin temp could have been higher from burning creosote. Either way I wouldn't use the color as an indicator.

Now if there was a picture of the double wall prior to cleaning and it was full of white ash left from burning creosote, I would take that as a reasonable indicator of a chimney fire.
 

MMH

Feeling the Heat
Jan 21, 2019
406
NV
I’ll admit I’m skeptical a bit also as if there is fuel in there it makes me think it wasn’t a fire, again curious about your draft. However, with that said, I’m also still skeptical that you may have had a brief chimney fire; if I’m understanding correctly you basically have a 90 to a 90 then vertical, if so I’m wondering if the fire could have been in the vertical portion and during that crusted up the creosote causing it to fall off landing in the section of turns/90s where it would have been difficult to burn it etc. perhaps unlikely but I think a possibility. Yes the discoloration is likely temp related, as long as the structural integrity is not compromised you should be fine and as others pointed out are rates for high temps etc. now that you’ve cleaned it play with it and see what you get. If your able to measure your draft post that update for the experienced people in here. Remember when it comes to creo it really doesn’t take a lot of build up to light it off, especially in glaze form.