A system for producing fluids from a subterranean zone comprises a tubing string disposed in a well bore, the tubing string adapted to communicate fluids from the subterranean zone to a ground surface. A downhole fluid lift system is operable to lift fluids towards the ground surface. A downhole fluid heater is disposed in the well bore and is operable to vaporize a liquid in the well bore. A seal between the downhole fluid lift system and the downhole fluid heater is operable to isolate a portion of the well bore containing the downhole fluid lift system from a portion of the well bore containing the downhole fluid heater. A method comprises: disposing a tubing string in a well bore; generating vapor in the well bore; and lifting fluids from the subterranean zone to a ground surface through the tubing string.