Flame variation

We have a Keystoker90 with direct vent and rheostat. With the same exact settings, we seem to get big variations in the flame size. Running at 50%, the flames easily hitting the top of the fire box, other times it's 6-8". Using bagged Blaschek coal. My only thought is that some bags of coal are wetter than others. Any ideas?

Depends on the feed rate, coal size and how much air passes thru the coals, our Keystoker/DV 90K does the same thing. Ours Varies quite a bit, from glowing orange to hitting the top too. Just depends on how it stacks up in the fire grate. The rice coal can vary in size and as it packs along the fire grate, less air can get thru, bigger sizes will let more air thru and burn differently. I run a small mix of Buckwheat (30%)/Rice (70%) or so, I just thow some handfulls of buckwheat to help elminate the clinkers/cakes from forming.

Nothing to worry about. The dampness of the coal shouldn't affect it, it will burn it off quite quickly as it's feeding.

I'm not sure how the direct vent affects it, but the flames in my unit vary depending on the weather. On days where it is clear and crisp there is more draft, even with the barometric damper wide open and it will pull a harder draft and make larger flames.

The DV should maintain a constant draft independant of the weather conditions, mine stays right at .03-.04 almost all the time, warm, cold, wind, etc....shouldn't make that much difference on the flame height, except the coal itself.