Best source of sizing and fuel usage would be one of the IR heating mfgs. Sizing is not like heated air systems.
They make a closed combustion tube style and an open radiant burner style. Open radiant is fine in a well ventilated space and tubes for tighter buildings with occupants.
“A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.”
― Robert A. Heinlein