The FV20 0 B-Vented model (4" B -Vent) is particularly well suited for replacement of wood stoves as it can utilize the existing wood stove chimney. The unit has a spill safety switch, which will shut down the appliance in case of a blocked flue or downdraft occurs.The FDV200 Direct Vent Model provides sealed combustion where it draws outside air for combustion. This model can be vented either horizontally or vertically.