An evaporator includes a housing, a bottle containing a substance to be evaporated, a wick having a lower portion disposed within the bottle and an upper portion protruding from the bottle, a heating device disposed within the housing at a position proximate to the upper portion of the wick, and an adjustment mechanism within the housing for displacing at least the upper portion of the wick toward or away from the heating device in a direction substantially perpendicular to the longitudinal axis of the wick. In a preferred embodiment, the adjustment mechanism includes a hollow cylindrical portion that engages the upper portion of the wick, and a dial portion for rotating the hollow cylindrical portion about an axis of rotation.