Clunkers ?

I have a Newmac combo wood - coal stove and am getting clunkers building up forcing the fire out about every 3 days. Am shaking a couple times a day , but why am I getting these clunkers?

Welcome to the forum.

Clinker build up usually is due to a few things, one is coal with a high level of impurities (anything that isn't actually coal, attributed other elements present in the coal vein), another is burning the coal bed at too high a temperature, making it easier for these non coal components to form clinkers. There may be other reasons that I can't think of, other members may reply with them.

Maintaining moderate stove temperatures and burning high quality coal will minimize clinker formation.

I doubt that clinker formation can be eliminated completely.

you're probably burning your coal bed too shallow which causes higher coalbed temps when trying to get a large amount of heat out of a shallow bed. the bed should be as deep as your furnace will allow you to make it, and adjust heat output with the air only.

Yes, I meant to say clinkers but I am a rookie at this ! I will try to fill up the bed of coals and see if this works. My furnace has a draft fan that blows down and under the grates so maybe a full bed of coals is better. It has a large firebox 16 x 24 and about 12 inches deep , so it holds alot of coal. It also has a plenum with a blower that comes on at a certain temperature. Ductwork is hooked together with oil furnace . Yes , I want my fire to last all winter without going out and I appreciate everybody's input , thanks.

Hello Vermonter, does the firebox in your stove have 'V' shaped, sloped sides acting like a funnel to funnel the ash down to a narrow center grate??

Clinkers are formed when the VERY hot coal ash is forced together by either poking the fire when hot, or shaking the fire when very hot.. anything that will cause the fine powdery ash to fall away, and let the super-hot ash to bump into other super-hot pieces of ash will cause clinkers to form The pieces of super-hot ash are molten sand, glass, and other minerals, and they stick together.

In a designed-for -coal firebox, the sides of the box are vertical, and the entire bottom of the firebox is composed of shaker grates... The ash will settle down without the ash being funneled toward the center grate which concentrates the super-hot ash together, creating clinkers.

The best way to reduce clinkers is as berlin said,, build a deep fire, and reduce the amount of shaking... to maybe only twice a day.. you want to be shaking cooler ash at the base of the fire, not red-hot ash that will stick together..

If your firebox is 'V' shaped, you will probably still need to clean clinkers out of the firebox every week or two.

This is what I had to do with my hand feed boiler with a 'V' firebox and central grate.

Greg L
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I have three grates that are 21 inches long and about 5 inches wide and are flat on one side. Firebrick lines the sides about 16 inces high. Maybe I shouldn't shake when they're hot and wait for the fire to die down a bit. I should shake at least a little every day though , right? I have been experimenting on how much to put in the fire box , everybody is saying to max out the fire box. Should I keep it flat and even or mound it a little in the center? There are times when it's burning solid red , is this too hot?
Mark

So are the three grates side-by-side? the grate area being approx 21"x 15" ? Are the firebricks lining the firebox vertical or nearly vertical?? If so, then you have well designed firebox for burning coal..

Yes, I would recommend filling the firebox to the top of the firebrick, mounded or level, really doesn't matter.. If the whole bed of coal is burning, then cut back the air to the fire some. With coal you want to control the heat output with the air to the fire, not by trying to control the quantity of fuel.

I would shake only often enough to keep the air passages through the grates open.. they tend to fill up with ash over a period of hours... I'd try shaking just twice a day, and see if this works or maybe three times a day.. But shaking when the fire is not at peak heat will help reduce the clinker formation.

It sounds like your are pushing the boiler for maximum heat output... when the coal fire is burning really hot, then you will get more clinkers... not much you can do about it. All coal has ash, and if the ash is very hot from a very hot coal fire, then it can and will fuse together some... Some coals more than others, and some grate/firebox designs more than others.. Can you try a few bags of a different brand of coal and see if it clinkers less??

Hope this helps... Greg L

My boiler has a V shaped fire box, I found the deeper I run the bed, the less clinkers I get. Like Berlin said, fill it. The larger mass doesn't have to burn as hot and you will probably use less coal. Coal isn't like wood where it takes a roaring fire to make heat. Coal wants to be a big mass of throbbing heat, more of it stays in your appliance and less goes up the chimney that way.

Thanks guys , I have been having better luck recently . I haven't lost a fire all week , still getting clinkers but I guess I always will. Leaving the ash door open for a bit helps get the fire going good on fill-ups , and you don't lose your fire. The warmer weather doesn't help right now , but will be ready for next year! Thanks again !
Mark