This would be a new term to me and I was in the business for 15 years!
Sounds to me like they are referring to the differences between white and red ash.
Here's the basics.
White ash is common in the north, it will burn up to a more powder like consistency and generally has a lower ash content. The coal will have a dark black shiny look. The ash content can go as low as 4% and be a very dense product but you're unlikely to see anything like this unless you're getting it from the Hazleton area and they didn't mix it with some higher ash white ash. This can be a problem keeping lit, it's not bad coal but instead too good.
The red ash has a more gray appearance, has more volatiles and will be easier to light and maintain a fire. It will also generally have a higher ash content and the ash will be more "chunky". You may also run into problems with clinkering if you try and fire it real hard.
sharkman8810 wrote:The " medium" for him is superior red ash, and the "hard" is blaschak white ash. For me both are good sources. My dealers comments were the "medium" didnt need as strong a draft and was easier to get going, and the hard was more draft and the stuff lasted longer and burned hotter. I don't necessarily buy his thoughts, superior red ash is a good product and is easy to burn and the blashcak isnt worth the extra $$
Correct, the BTU content on Superior is very high but the ash content is something like 14%.... Generally speaking the BTU content on white or red is going to be in the same area.