Questions about clay ovens?

Hi:

I am looking for a tandoor clay oven that can be fueled by bituminous 
coals. I've looked at many shops on and off the net. I've not been able 
to find one that I'm sure is safe to use bituminous coals on. Some use 
charcoal but I don't know if its safe to use bituminous coals on these
oven.

I feel gas and charcoal are too bland. They don't give the flavor I 
like. To my nose and taste buds, nothing is more pleasant than garlic 
naan cooked in a clay oven fueled by bituminous coals. The earthy aroma 
of the clay combined with that of the bituminous coal really gets me 
appetite going.

Also, what type of heat is mostly used in clay oven to cook food -- 
radiant, conductive, or convective?


Thanks,

Radium


P.S. I dream of eating some heavily-buttered garlic naan cooked in the 
above manner with some equally-delicious butter [makhni] tandoor chicken 
curry sauce.