Direct-vent: These units will always have a sealed glass front with either a safety barrier screen or double glass. They are generally more heat producing (efficient) and have the ability to be vented out the side wall or through the roof. The direct vent draws its combustion air from outside while venting to the same outside atmosphere.
B-vent appliances: These units are open face for a more natural true fireplace look. They will give off radiant heat but are not very efficient. These units must be vented through the roof and restrictions on minimum vent run will always be a factor in determining if they can be used.
Wood burning with gas logs: Due to the fact that wood burning fireplaces can accept/burn more BTU’s these will always be the best looking traditional log style fireplaces with the biggest flames. They also have less restriction on opening sizes. They are open face, must be vented through the roof, and will have either operable glass doors or a power damper.