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Grizzlyman
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# Posted: 18 May 2025 08:34pm
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I noticed this weekend a discoloration on our chimney.
It was 85 last weekend but only 45 this weekend and 34 at night. We ran the stove all day yesterday with the door open (so basically just like a fireplace)- not a real hot flue. did not hear any significant sucking or other indication of a chimney fire- I doubt it was from this weekend but idk. it’s possible I just never noticed the discoloration before.. I did clean the chimney out last year from the bottom toward the end of the year. I did run it a few times last year after the cleaning - it’s possible I didn’t get the very top of the chimney cleaned. We did notice what might have been a small chimney fire last year at the very end of the year with some sparks but it didn’t last very long.
Is this heat discoloration? I think it probably is but don’t know. Read a bunch of stuff online where it might just be smoke discoloration and washes off.. but I’m not sure. It looks to me like there was a hot spot and it radiated outward from the center of the mark.
What do the wood stove experts here have to say?
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travellerw
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# Posted: 18 May 2025 09:37pm
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Correct me if I'm wrong... but that is a insulated pipe?
Its my understanding that modern insulated stacks don't get hot (on the outside) at all. You can touch them and they might be slightly warm.
Anyway.. If it was my chimney, I would go up , take the cap off and check things out.
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Grizzlyman
Member
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# Posted: 18 May 2025 10:25pm
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Correct! It’s insulated and isn’t supposed to get hot!
That why I’m wondering what is going on with it. I will definitely be checking it out.
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gcrank1
Member
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# Posted: 18 May 2025 10:39pm
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Looks like the discoloration I got on my stainless steel motorcycle muffler  , for sure from the heat.
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DRP
Member
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# Posted: 19 May 2025 06:49am
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Looks like heat and possibly settled insulation. look near the tops of each section as you go down.
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Grizzlyman
Member
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# Posted: 19 May 2025 07:45am
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DRP meaning the insulation settled inside the pipe and therefore the top part is no longer insulated?
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gcrank1
Member
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# Posted: 19 May 2025 08:17am
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Im thinking that if that is the case it wont matter way up there.
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FishHog
Member
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# Posted: 19 May 2025 08:19am
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Bit of a downdraft heated the top of that pipe would be my guess. But yes sure looks like heat discolouring
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Brettny
Member
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# Posted: 19 May 2025 08:42am
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Insulated pipe does get hot..that's why theres a minimum to combustibles. A bit of change of color isnt out of normal. Your chimney cap still looks new so that's prob hardly used/hot.
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Grizzlyman
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# Posted: 19 May 2025 10:18am - Edited by: Grizzlyman
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DRP
The other top section is inside the storm collar. Can’t inspect it from the outside. I would think if the other section had a hotspot near the top it would have discolored the storm collar as well. That’s just thin gauge galvanized steel. But idk.
FishHog
That’s what I was pondering too. Downdraft heated the outside of the pipe. Agree it probably doesn’t matter up there.
Brettny
You’re right It does get hot still-but can usually touch it still- even if it’s just for a second. need
2” clearance for that reason, but shouldn’t be anywhere near hot enough to discolor outside. I think stainless needs 600* plus to discolor that way.
Would have to be a downdraft wouldn’t it? -being as it’s at the very top. A chimney fire even in double wall should still be not anywhere near hot enough to get through the insulation.
The only thing I can reason is hot gases flowing out and down the side.
BUT if that were the case, shouldn’t the discoloration START at the top and work its way down? Looks kind of like there’s a hot spot about 2-3” below the opening.
EDIT: Now that I look at it again there is a small collar on the chimney cap. Gas would need to flow down and around the collar to touch the pipe… which makes sense that the hot spot is not directly at the top.
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DRP
Member
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# Posted: 19 May 2025 08:40pm
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My comment was from a few failures I've heard of. Those joints are little danger, what I was wondering about was the inside joints, can you see them and are they discolored at the top? If so I would check the temp of nearby combustibles when you're under fire. I would say no matter what to have 600 at the top of the stack there was probably a flare outta it. Its usually hard to get the "load it and choke it" folks to keep it above 190, creosote, at the top. There is a UL standard, I think a class A survives 3 2200 degree events? That is fuzzy.
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Grizzlyman
Member
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# Posted: 20 May 2025 12:38am - Edited by: Grizzlyman
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DRP
I only have one joint. I have black pipe up to the cathedral ceiling box. Then one double wall through the box and roof assembly. The one joint in the double wall i have is inside the storm collar above the roof.
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Brettny
Member
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# Posted: 20 May 2025 07:39am
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Harbor freight sells a temp gun and I believe there under $25. There also usefull for a ton of other things.
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