A vapor-to-air heat exchanger for an aircraft powerplant that includes: a pressurized vapor source supplying vapor; and a condenser including a condenser inlet in fluid communication with the pressurized vapor source to receive the vapor, a condenser outlet, and at least one pneumatic vessel defining a cavity in fluid communication between the condenser inlet and the condenser outlet. The pneumatic vessel is reversibly inflatable to be configurable between a collapsed vessel configuration and an inflated vessel configuration. A volume of the cavity is greater in the inflated vessel configuration than in the collapsed vessel configuration. The pneumatic vessel is inflatable from the collapsed vessel configuration to the inflated vessel configuration when the cavity is pressurized by the vapor.