Here are pictures of the Coal Bear with bricks removed and grate supports showing along with the angled ash deflectors directing ash into pan;
View attachment 286403
View attachment 286404
Coal grates need to set in a frame to fit the firebox which is 20 inches deep x 18 1/2 wide. This makes the frame 19 1/2 x 18. Grate support frame will rest on the horizontal existing supports. This allows 351 square inches of grate area which can be loaded approximately 6 inches deep. This is well over 100,000 btu max, and would normally operate near 60,000 btu burning efficiently. (6 inch pipe and chimney with barometric damper)
The choice of grate design and how it is cleaned make the difference between easy cleaning, good operation and forming clinkers, and causing airborne fly ash.
My favorite grate system is the Gibraltar which changed to Glacier Bay. They are long, extremely heavy duty cast iron grates that resemble cam shafts. They mate and mesh together like gears that roll and grind the ash off coal with a minimum of burning coal falling through, and I’ve never formed a clinker in one.
Flat plates that rock tend to build up ash in the center and when rocked too far are designed to dump the fire through, or get coal stuck easily between when rocked too far, then wait it out to burn out before it can be shaken and grates level again. There is a learning curve of the best shaking method and motion depending on how deep the ash is.
With any type movable grate if only touching up a fire before bed or leaving for 8 or 10 hours a short jerky motion, short stroke, allowing the play in shaker linkage or loose handle fit “knocks” with a vibration to clean until very few coals are seen dropping in ash pan. After many hours when coal burns down and has lots of ash under it, a slower, longer stroke rocking motion dumps a lot of ash quickly
European grates do not move, and are cleaned with a slider knife. They are the easiest to make and don’t require any means to shake or rock. They require slots in the front to pass the thin sliced knife through and normally have little gravity doors on the back that tilt upward when the knife is inserted and slid the knife sideways across the flat grate surface. It resembles a long thin letter opener. I find ash leaks out of the holes during cleaning becoming the dirtiest type. Slots are usually smaller to burn pea size coal, which gives a much longer duration fire between cleaning at a lower output.
You will get the same btu output per pound of any size coal, the difference is how much space for oxygen between each piece making larger pieces burn faster. Any grate for Chestnut size coal is fine.
Always stoke ( the act of shoveling or pouring in fresh coal with a hod) leaving a shallow spot, not entirely level so there is blue flame like a pilot light to ignite coal gas as it is expelled from fresh coal. Loading in the shape of a horseshoe works fine, or a hollow spot front and center that ignites quickly so it has an ignition source on top. Secondary air is needed from upper air control to allow oxygen on top of the fire for secondary combustion of coal gas. That is a lot of heat and pollution to let out without igniting it in the stove. The upper intake only needs to be cracked open slightly. More than that allows indoor air up stack cooling it, decreasing draft. If you don’t have ignition from lack of air, you will get it when opening door. It can be a scary flash of blue flame in the entire firebox area leading up the stack that you learn real quick to open slowly and avoid. No denying, it is a mini explosion. Coal dust can ignite the same way when heated and conditions are right, so keep things clean of coal dust inside.