What to do with clinkers?

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May 8, 2018
New York
Sorry for this, perhaps, very dumb question. I've been burning in a fireplace insert (Napoleon 1402) for 14+years. Stainless steel lined chimney cleaned annually. This year only, I've been noticing every night I load up the insert and wait for it to be really blazing before I lower the throttle/choke down to 1/4 and go to bed. In the morning, there's few embers left. But a lot of these heavy chunks of black stuff buried in the gray ashes which sound like "clinkers" from what I've read elsewhere on this forum. It almost looks like chunks of asphalt, each are at least 2" thick and of varying length from 2"-4". If I restart a fire, they eventually go away but they're not particularly flammable like charcoal. I've NEVER had this happen before in the years I've been burning. I've included a photo from the ash bucket. Should I just leave them in the stove to be consumed over time? They don't seem particularly flammable. Am I burning incorrectly and getting this as a side effect? Is this an indication of a heavy creosote buildup elsewhere (more than usual)? I'm not sure what wood I'm burning because it's been over a year since I split/stacked that pile and have no clue who gave me the logs anymore.
Any comments appreciated.

Oct 15, 2020
New Hampshire
My only knowledge of clinkers is as a hobbyist blacksmith. They're formed from the garbage trapped inside coal (when forging). They tend to block airways and are removed after a day of forging and discarded. Of course you want to be careful as they can get hot and trap heat. I think you'd be best served removing it from the insert when cooled completely off.

Someone else I'm sure will chime in with a more solid answer. I'm curious where the stuff to make the clinker came from. I didn't think wood produced anything but ash unless you're burning wood with metal in it.


Chimney sweep
Staff member
Jan 14, 2014
central pa
Yeah it happens at times allot depends upon wood species higher silica content wood seem to do it more. Just remove and dispose of the same as ash


Minister of Fire
Oct 16, 2019
I had a lot of them in fall when I was burning silver maple from a yard tree. Then they were rare burning "woods" beech and sugar maple, now I'm burning more ash from a yard tree and getting more of them again. Someone posted in another thread it's from mineral content. Suppose in town more likely to fertilize...


Minister of Fire
Dec 28, 2006
Mt. Rainier Foothills, WA
I get them all the time burning doug fir with bark. It's just minerals like sand in the fuel. If you've ever thrown a beer bottle into the fire you know that a fire is hot enough to melt glass and also melt sand into glass. They like to form where the fire is hottest near the intake. I try to break them up but they remelt and reconnect. The only thing I warn you about is that they can stick very well to firebrick if you don't have sufficient ash layer under your fuel. When they stick to the firebrick you will eventually have to pop them off with a little force and I have lost quite a bit of firebick thickness since the bond to the clinker is strong enough to peel off a portion of the lightweight firebricks in many modern stoves. I don't have that problem with the old school dense firebrick.


Minister of Fire
May 26, 2020
Yeah I've had a similar experience. A lot of the wood I get is former yard trees from tree services so I've seen these a bunch, particularly with one batch of ash I had. I just smash them up and/or shovel them out and move along with burning. Nothing to see here folks!


Burning Hunk
Jan 14, 2015
Weeping Water, NE
We live in limestone country so most woods will produce clinkers but I find elm to be the worst. I have large ones that I just pull out and set aside on the cement floor to cool. Once cool they seem to almost disintegrate into dust when messed with. I just put them in the can and throw them in the garden or barnyard when I dump ashes.

I second what Highbeam said about them sticking to the firebrick. Seems like every once in a while one will try to attach itself permanently to the brick on the bottom of the stove right about in the middle at the front edge.


Minister of Fire
Oct 20, 2018
I walk around the yard with a collander in one hand and ashes in a small paint bucket. I shake ashes onto my lawn and rub and solid pieces into the collander.


Minister of Fire
Nov 18, 2018
Downeast Maine
The floor of my cookstove has about 3" of hard "clinker" because I haven't taken the ash out in months. If the flame of my butane torch hits "fresh" ash it kind of shrinks like melting foam and appears to turn into the dark clinker. My cookstove will run hot if I am baking at high temperatures with the bottom fed air, even if the slider is closed. My grate is mostly closed off with clinker and there is only a small slit where air comes in. In another month I'll have to break out the clinker since it is beginning to cut into the firebox volume in a negative way. Last winter I cleaned the ash into the pan more regularly and didn't get the clinker build up. My goal was to let the grate close off most of the way and it worked.