Preventing fires at chimney cap

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Deb_in_MN

New Member
Jan 11, 2021
1
Bruno, MN
Hello, first post here. I have been running a professionally installed Lopi Liberty wood stove for about 12 winters now. The stove is located in the main room of the house with a cathedral ceiling about 26' high at the peak. The chimney goes straight up to the peak, taking only a greater than 90 degree turn to avoid a roof beam. I try to burn only seasoned hardwoods (mainly oak this year). When my first husband died in 2017, one of the first things I did was to have the chimney professionally cleaned and inspected; the inspector found no issues. We had never had a chimney cap fire prior to then.

Fast forward to yesterday (and a couple times since I remarried). Yeah, it happened. Scared the hell out of me, but I do have a steel roof and there is snow on the ground so we were safe. My husband went up and pulled the cap afterwards and threw it on the ground. It looks like a lot of creosote had built up right at the cap. For now we're running it without the cap, no chance of any wildlife etc getting in there for now. But, this is not the first time this has happened, and I would not like it to happen again. My husband does clean the chimney 1-2x a year, but somehow we're getting creosote building up at the cap.

My husband is the main wood stove tender and I appreciate that, but he has this annoying habit of closing the damper at night, or even any time he gets a good fire going during the day. There is a magnetic thermometer on the stove pipe, and I was always taught to keep the fire going at 300 degrees F or so. When he closes the damper, of course it runs cooler than that. And he pushes logs in there side by side, so I think air flow is restricted.

Could the burning at cooler temperatures be contributing to creosote buildup at the cap? Could throwing in wood that still literally has snow on it have any effect? Trying to win an argument here. ;) Any other tips for preventing creosote buildup at the cap?
 

gthomas785

Minister of Fire
Feb 8, 2020
530
Central MA
Yes, and yes. Run the stove hotter and only use dry wood.

One thing that concerns me is that you used the words "seasoned" and "oak" in the same sentence. How long has it seasoned? Oak is notorious for drying slowly and can take several years to be fully dry. Do you have a moisture meter? If not, getting one and learning to use it correctly (bring wood inside for 48hours, then re-split it and test the moisture on the freshly split face) may open your eyes to the true moisture content of your wood. And they are pretty cheap.

And regardless of how dry the wood is in the inside, snow/ice on the outside of the wood is not going to help your situation.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
90,612
South Puget Sound, WA
Is the stovepipe that goes up inside the house to the chimney support box single-wall or double-wall stovepipe? It sounds like single-wall when really should be double-wall for that long run. Single-wall connector shouldn't be used on runs longer than 8'. The single-wall pipe is losing too much heat and cooling the flue gases to the point where they are condensing as creosote at the top of the chimney.
 
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xman23

Minister of Fire
Oct 7, 2008
2,352
Lackawaxen PA
If i'm understanding correctly it was not a chimney fire, but just the cap? How are you cleaning? When the cleaning was done was the cap removed and cleaned? Is there a screen in the cap?
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,612
South Puget Sound, WA
There is a magnetic thermometer on the stove pipe, and I was always taught to keep the fire going at 300 degrees F or so. When he closes the damper, of course it runs cooler than that. And he pushes logs in there side by side, so I think air flow is restricted.
You are correct. If the stove pipe is single-wall then keeping it at about 300º surface temp until the wood is at the coaling stage is a good idea.
 

peakbagger

Minister of Fire
Jul 11, 2008
6,616
Northern NH
If he loads it up and cranks the air down before going to bed he is setting up for heavy creosote formation.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
90,612
South Puget Sound, WA
If he loads it up and cranks the air down before going to bed he is setting up for heavy creosote formation.
Yes, there's a good chance that the fire was in more than the cap too. That could just be where the creosote was the thickest and took the longest to burn off.
 
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Stinkpickle

Minister of Fire
Jan 13, 2015
587
Iowa
There is a magnetic thermometer on the stove pipe, and I was always taught to keep the fire going at 300 degrees F or so.

I have about 8' of single wall on an old smoke dragon, and I try to keep it at least 400 degrees. It makes a big difference.