Can’t keep the fire going Hitzer 30/95

So usually I light up my coal stove in my garage the weekend before New Years and run it till mid March. This year I lite it the weekend before Halloween as I had a bunch of stuff I had to do in the shop and figured it be more cost effective to burn the coal 24 hours instead of oil for 6-8 hours 3 or 4 days a week.
My issue. Burns quick and hot when it burns and won’t last for a 12 hour shakedown. Otherwise I fight with it to get the fire to come back. Once back, 5-6 hours into the burn stoves @ 550. 8-10 hours into the burn and it’s starting to burn it self out.
It’s getting quite tiring to have to waste the time to recover the fire.
Stove is a Hitzer 30/95. Single wall out the stove into a baro up 13 feet through the wall into double wall insulated which runs 10’ up the outside of the building.
Chimney temp when burning good @ 150
With @ .05 on the Manometer.
Personally I think it’s a temperature issue with the chimney.
I have been contemplating buying more double wall chimney pipe. However I spent a small fortune already as I bought chimney block and flue pipe to erect a brick chimney inside the building.
Tell me what you think , any and all opinions are welcome.

Leaky bottom door gasket or an unknown leak somewhere under the fire is my guess with the temps its running at. Check the hopper gasket while your at it, looking for coal crumbs on the top of the gasket. It should run at a low temp if thats what you want, just by using the bimetallic set low. Your draft is not excessive at .05

Sounds like strong draft and leaks like warm said. How much primary air?

Zero primary air. Ash door slide is keep closed.
As long as it’s burning and the chimney is hot, it has a good vacuum on the chinmey @ .05. Once the chimney temp drops so does the vacuum.
I’m thinking if it was just a lower door issue I wouldn’t be loosing the fire as quickly as I am.

Is the hopper totally full ? Since its losing draft after being warmed up the leak is happening above the coal bed , double check everything ( i have 2 shorter than recommended double wall chimneys 10' and 13' the only issue is I need to start them drafting if it's over 30*'outside ) cover baro with foil when the problem repeats and see what happens

Hopper is totally full.
Chimney is @13’ single wall then double wall through the wall and up another 10’ with double wall insulated.
It burns good and hot once it’s fired up. It just doesn’t like to keep an even fire going. It’s hot or it’s not.
The single wall pipe joints are all taped with metal duct ducting tape.

burning a full load in 8 hours ( should be excessive overdraft, but losing draft too is stumping me ) manometer or using the weight setting for the .05 measurement?

Sounds like all or nothing....did you foil the bar damper? Is the wind knocking down your draft? Is the top of the flue below the height of another nearby roof or tree? What are the outdoor temps? How bout humidity? The flue isn't staying warm enough to keep a good vacuum going. I realize you probably already considered all of what I mention but also make sure there are no leaks in the flu connections or any air being pulled across the top of the fire through the door. 8-10 hrs sounds normal to me.....how many lbs of coal would this be?

Yup burning a full load in less than 8 hours. Otherwise it goes out. All or nothing.
I didn’t foul the baro. I didn’t even think of it. All the chimney connectors are taped. I check the door and tightened up the front door locking pin. It make the door more snug but didn’t make any burning changes. Today has been 50 I’m in new Paltz NY (southern NY) an hour north of NYC and an hour south of Albany. Chimney is @ 6, above the center of the peak with no other roofs in the area. As for humidity- today it rained

Warm rainy days are tougher to keep a coal stove going.

Have you tried opening a nearby window about an inch ? Might be that your house is a bit too airtight ???

Paul

Is anything different from last year? Other than starting earlier? It sounds like strong draft to me. Yeah you say it drops off but that's because fuel is dwindling late in the burn, decreasing temps and draft. Is draft set with manometer? My exhaust temp going into thimble is around 100 when I'm running stove at 475ish. That's 12 ft of pipe though.

Each stove and chimney setup responds differently , My stove will continue drafting at very low stove temps until mid 60s outside than I need to cover baro and open air to keep going .

Double wall pipe outside or class A insulated chimney pipe?

There is a difference.

I replaced an ash pan door gasket last year and I didn’t scrunch it all into the door channel. It’s certainly not as tight as the previous gasket and my draft is just slightly higher on the mano . Upon replacement again, I’ll scrunch it together more and make it tighter next time just for peace of mind.

Sunny boy. Its my garage. It’s 24x40 steel building that is poorly insulated. It has a lot of air leaks and drafts.
Waytoomany? - stove and piping is exactly the same as last year. Same with the insulation on the doors. Only change is the date and temperature. I usually start the garage coal heat the weekend between Christmas and new year’s. The high temp during the day then is typically between 20-30. It burned a lot of coal last year but it would go 12 hours. Between tending.
Hoyt man - class A insulated through the wall kit with 10’ going straight up @ 5’ above the peak.
Both the door and the ash pan gaskets were replaced last year and so was the load door on top. All replaced before I put the stove in service in the garage.

Over all this is why I’m stumped. It doesn’t make much sense.

Little air…little fire.
Excess air…excess fire.
Controlled air…controlled fire

Assumes primary air supplied from bottom of grates. And grates are cleared as not ash bound and restricted of free movement of primary air. And adequate draft not to restrict exiting of exhaust.