Abstract: A multistage evaporation boiling equipment is disclosed in the form of a single unit, each stage operating at a different pressure. Two or more bundle type heat exchanger units are horizontally positioned along a central column, part of which units protrude from the column. Attached to the protruding part of each unit is a flange which is covered by a sealing tube wall. A cover over a passageway communicating with this sealing tube wall provides a second seal. One or more walls inside the column separate the heat exchanger units. Openings, which may hold a choke means, are found in the separating wall to control passage of vapor.