Coal and charcoal have nearly the same BTU value per pound (my pocket reference lists 24.74 million BTU/ton for coal and 25 million BTU/ton for charcoal). However charcoal is much less dense so you will be feeding the fire more often and use a greater volume of charcoal. They both have an upper limit of around 4000 degrees F which is much hotter than anything you would normally need. Coal puts out more smoke when is cokes off (charcoal is already "coked"). Charcoal needs much less air to get hot and really works better with side blast and good insulation.
I use coal for 3 reasons. 1 I can make it myself so cost is time invested, 2 my current set up won't adequetly vent the coal smoke without a fan and 3 goo coal can be a real bear to find 'round these parts.
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