On-demand, hand-held vaporizer that operates primarily by convection. The vaporizer is configured to permit very rapid (e.g., within a few seconds) heating of air drawn through an oven chamber to a predetermined or selectable vaporizing temperature to vaporize a material (e.g., loose leaf plant material, etc.) that is held in the oven chamber. The vaporizer provides efficient transfer of air being heated as well as rapid delivery of vaporizable material to a user.