Condensate Return Lines

All condensate lines should be pitched down 1/4" per 10 feet (5 mm/m) to allow for drainage of the condensate by gravity.

The most efficient return systems are, by design, not completely full of liquid and are not vented to the atmosphere. They are referred to as dry-closed systems. They handle condensate at steam temperature (i.e. not sub-cooled). Condensate return lines are specified to carry a condensate load, in pounds of condensate per hour (kg/hr). In fact, most of the condensate flashes to steam in the relatively low-pressure return line. Because the volume of flash steam is so much greater than the volume of the condensate, the return lines actually carry about 96% to 99% flash steam by volume. Therefore, condensate return lines should be sized to maintain a reasonable velocity of flash steam (under 7,000 fpm/30 m/s) at an acceptable pressure drop for the specified condensate flow rate.