Are Hard ash / clinkers problematic?

[Jason H]

Hi there, first post on this site! First clean out of my wood burning insert revealed these beauties. From what I've read, they're called clinkers.


I've burnt almost exclusively elm so far this season which had been standing dead for many years.

Are they bad for my catalytic insert?
Is there anything that I use them for?

 

[Highbeam]

Sometimes they fuse to the firebrick so when you take them out you lose a chunk of firebrick too.

 

[moresnow]

How long has your dead standing Elm been split and stacked prior to burning? I've had it still take a year at least to season. Curious.
Clinkers aren't completely abnormal or unheard of. No real use for them that I am aware of! Chuck them out.
What make/model insert are you running?
Welcome to Hearth.

 

[ckr74]

Seems like Elm is the worst. I've never had them stick to a brick but I keep a layer of ash in the bottom. They don't seem to hurt anything but I don't have a catalytic stove.

 

[Jason H]

How long has your dead standing Elm been split and stacked prior to burning? I've had it still take a year at least to season. Curious.
Clinkers aren't completely abnormal or unheard of. No real use for them that I am aware of! Chuck them out.
What make/model insert are you running?
Welcome to Hearth.

Thanks for the comment. It's a regency 2700. With both burn tubes and a cat.

I split it early spring, stacked open in the sun and breeze, so it's been only 6 months. Havent checked the moisture of the logs yet either.

 

[begreen]

Clinkers are formed from fused silicas that were in the wood. Bark will have the most. They don't affect stove performance.

 

[huauqui]

Clinkers are a regular occurrence for me with Elm. All the elm I have has no bark, has been cut, split, and stacked for a couple of years and tests between 15-19 percent. I have found no way to burn it without getting them regularly so I simply clear them with my ash shovel prior to reloading. I had almost a whole rack last winter that was sub 15% and burned exceptionally fast but left clinkers too.

 

[Orerockon]

Sometimes they fuse to the firebrick so when you take them out you lose a chunk of firebrick too.

I'm just starting to get these but I put new firebrick and combustors on and I'm finally getting hot enough fires to light them off. I get that it's gonna happen reading posts here but some of it is just impossible to get off the firebrick. It's new brick (I replaced all of it when I installed the combustors) so I really don't want to be breaking it and replacing with more new bricks (too expensive to keep buying new boxes). Any tips on how I might prevent this? Leaving a few inches of ash like Firecat suggests on their combustor FAQ doesn't stop it. FWIW I'm burning all thoroughly seasoned maple (tested with a moisture meter at 7-10%).

 

[Grizzerbear]

I don't know of any way to stop them. It's a characteristic of the wood you are burning. Fwiw I have them every time I empty the ashes and I burn nothing but hickory and oak. I have never had one fused to the firebricks.

 

[moresnow]

Normal. Gently remove the easy stuff with your poker when removing ash, then work around the tuff parts during burning season. Not worth busting fire brick over unless your a finger nail chewer kinda personality

 

[begreen]

They come from silica in the wood getting fused together. The silica can be concentrated in the bark. They are common. Some wood species create more than others.

 

[David.Ervin]

I get those when I have a really hot pile of coals on top of ash left by something with bark on it, usually right in front of the air inlets where it'll get blast-furnace hot. Just whatever minerals in there melting together I guess.

 

[Orerockon]

I don't know of any way to stop them. It's a characteristic of the wood you are burning. Fwiw I have them every time I empty the ashes and I burn nothing but hickory and oak. I have never had one fused to the firebricks.

Yes I think it was the tree itself. It was a large maple I got for free, I burned through most of it then started on another maple from a different person. The clinkers more or less stopped, but I still occasionally get one. I found another site that referenced a paper about it, it's very thorough (and confusing, and boring). They basically chalk it up to mineral-y wood and hot temps. If the ash has enough mineral content and the fire gets hot, they tested 1400 deg. which is about the max I get when the combustor is on. The ash fuses if there's enough calcium and potassium in the wood. Which makes sense for me because I replaced the old combustors in my stove and probably didn't get a really hot fire for 10 years. And I'm not sure how i works but I would guess the temperature of the large mass of coals, that is what is actually keeping the combustor hot enough to be working, may get hot enough to fuse the ash. They tested several tree species, the only one I burn is oak. They didn't say which one produced the most clinker. At the end they say that more work needs to be done, apparently it's not something that has been studied very much. Their paper focused on large biomass burners, like you see at a lumber mill where they burn the bark and scrap to make steam for the mill. Interesting stuff indeed.

 

[Woodsplitter67]

Iv gotten a few here and there. Mostly happens when I go longer in between clean outs.. and don't rake the ash

 

[SpaceBus]

I get a lot of clinker in my cookstove, but I like to let the ash build up for a few months before I take it out. The clinker makes a great traction aid/ice melt for my driveway.

 

[NickW]

I seem to get a more clinkers in shoulder season burning silver maple or burning "town" trees. This year I burned an ash & silver maple from town, and beech and sugar maple from woods. No clinkers from the beech and sugar maple...

 

[stoveliker]

I have burned mostly maple, oak, sassafras and a bit of cherry. The sassafras consistently gets me a lot of clinkers (as in half the ash surface is "clinkered").

So certainly this has to do with wood type. And likely temperature as well.

 

[Grizzerbear]

Yes I think it was the tree itself. It was a large maple I got for free, I burned through most of it then started on another maple from a different person. The clinkers more or less stopped, but I still occasionally get one. I found another site that referenced a paper about it, it's very thorough (and confusing, and boring). They basically chalk it up to mineral-y wood and hot temps. If the ash has enough mineral content and the fire gets hot, they tested 1400 deg. which is about the max I get when the combustor is on. The ash fuses if there's enough calcium and potassium in the wood. Which makes sense for me because I replaced the old combustors in my stove and probably didn't get a really hot fire for 10 years. And I'm not sure how i works but I would guess the temperature of the large mass of coals, that is what is actually keeping the combustor hot enough to be working, may get hot enough to fuse the ash. They tested several tree species, the only one I burn is oak. They didn't say which one produced the most clinker. At the end they say that more work needs to be done, apparently it's not something that has been studied very much. Their paper focused on large biomass burners, like you see at a lumber mill where they burn the bark and scrap to make steam for the mill. Interesting stuff indeed.

If it's any consolation I've been getting mega clinkers this year. I had a guy spread lime in some pastures that have a lot of broomsedge in them. The lime raises the ph of the soil and therefore reduces broomsedge. Well right before he was entering the field he turned his spreader on.....just so happens some of my stack are right there...and completely covered one side of two stacks. I knock off as much as possible before bringing it to the porch but that stuff sets up pretty hard so inevitably some goes in the stove. Clinker city and I'm going to have to deal with it next year too. Live and learn. I'll make sure that guy waits until he is in the pasture next time lol.

 

[jetsam]

They're harmless for wood burners.

Coal stoves have air intakes on the bottom and do not like clinkers.

 

[SpaceBus]

We burn about 90% fir and spruce and they seem to give us plenty of clinker. Like Jetsam said, it can be a problem if you have a grate with air moving through it, but I use this to my advantage. I let the clinker cover up all but a small pilot hole on the cookstove bottom grate. Same with my Morso, but it doesn't have an air inlet through the ash pan so I just let the grate totally cover up.

I suspect the clinker is forming due to high Calcium/Calcium Carbonate in the wood/bark. After you burn that wood/bark it leaves behind a nice white fluffy ash. From what I can tell the clinker is formed from burning that ash a second time. I noticed it when lighting my cookstove with a larger butane torch. The white ash in the path of the butane flame visibly shrank, appearing to burn again.

 

[Orerockon]

I seem to get a more clinkers in shoulder season burning silver maple or burning "town" trees. This year I burned an ash & silver maple from town, and beech and sugar maple from woods. No clinkers from the beech and sugar maple...

I burn some town trees too, when I can beat the Craigslist sellers to them. I've seen some big trees that they got to first and took all of, then ina week or so listed for sale. I could tell because they were ornamental trees like sweetgum (ew). Even saw an Alianthus go right back up. Like burning paper lol. I haven't paid for firewood in many years except I bought a few whole trees cheap (like a 200 year old oak for $200 and sold the 4 foot wide trunk to a speciality wood seller for more than that).

 

[Woody Stover]

I leave them in the stove sometimes and pull them to the front. They seem to prop the wood up out of the ash, and those splits in front get burning fast with air underneath them.