This works well for full 40lb bags...
As far as dust control...cut open bag fully...lift bag up to hopper...with one hand under bag and other hand keeping opened bag closed by overlapping the cut... all in one motion invert bag and lower it (still overlapped) into bottom of hopper and get hand out just before landing it...relax now...all you need to do now is grasp the upper corners of the now landed bag and wiggle and tug gently as you lift the bag while the coal slides out nicely on top of the existing coal or bottom.
I guess if you wanted less than full bag...you could make partial bags up ahead of time outdoors and have them nearby for when needed.
Even a coal hod or coal scuttle, bought at stove and hardware store, would allow the coal to slide out and into the hopper w/ less dust.Pictures of hods and scuttles
coal from the bag over the stove...the free falling coal will always make a lot of airborne dust.