Harman Magnum Post Burn Clog

Hello. I recently bought a home with a Harman magnum coal stove and have a small issue. At night the coal burns and condenses into large chunks that end up clogging the exit way to the ash pain. This creates a very unfriendly smell. Any advice or what causes such an issue? Using anthracite rice coal that forms into large grey ash chunks/bricks during burning and post burning. Thank you

What kind of coal are you using?

Are the ashes white or red?

using anthracite rice coal, ashes are grey/white are large chunks or brick like during burning/becoming ash

They're called clinkers...melted/fused ash due to excessive heat.
Too much air...block off more intake at combustion fan.

I don't think you have anthracite coal .

Sounds more like your burning Bit coal.

the 'unfriendly smell' if it is like rotten eggs or a sulfur odor is most likely co seeping out of the stove and you should shut down until you figure out the cause. do you have co monitors?

as mentioned if it is anthracite coal, some varieties will clinker up more than others when given too much air. do you know what brand coal it is (name on bags) or if bulk which breaker the delivery came from?

too much combustion air being blown through the grates can cause exhaust to seep out places other than the flue. the space around the glass, back through the hopper are places it will come out. there should be a plate that rotates to cover the inlet on your combustion fan. do you have one and how much of the fan inlet is open? mine is open about an inch at its widest from the arc of the round inlet.

do you have moisture on the underside of your hopper lid? that would indicate exhaust coming back through there.

what are the settings on your control box? what does the burn pattern look like on the grates at full burn and during 'idle' mode? how much ash is at the end of the grates during a full burn, about an inch?

The issue may not be "clogging". He may have poor draft and or too much combustion air and it's backing into his house. He may think it's clogging because the ash builds up on the grate in piles when not at a higher heat output as we all know. If you read his post he states it is his opinion that the build up is causing the backup into the room. That may not be the case. A manometer is called for here.
Hopefully it is just bad coal and or improper feed rate and or combustion air adjustments.

Some Magnums somehow end up w/o any combustion fan adjustment plate/flap...for sure too much air.

The fused rice coal ash comes off the grate like it were extruded and sometimes gets long before snapping off, and may snap back aways and pull some of the fire w/ it into ash pan.

I'd say too much air.......