The total annual costs are compared for standard rectifiers and two-enthalpy feed rectifiers, which condense part of the feed and feed this liquid above the vapor feed. For new equipment total annual costs are very close. However, if condensing distillate requires refrigeration but condensing feed does not, the two-enthalpy feed rectifier has significantly lower total annual costs. Retrofitting from standard to two-enthalpy feed provides a relatively inexpensive capacity increase but with a slightly lower yield. The two-enthalpy rectifier system also has excellent turndown properties. All results were obtained for feeds with low to modest amounts of more volatile component.