Forced draft vaporizers are designed for customer station, distribution and plant back up applications where high flow rates are required and space is at a premium. It utilizes forced convection as the heat transfer mechanism. Multiple fans mounted at the top of the vaporizer force high velocity air downward through the heat exchange array providing maximum heat transfer and high evaporation rates. The vaporizers comprise a number of individual multi-finned heat transfer extruded elements connected in various series and parallel paths to meet the exact requirements of individual applications.