Abstract: A system for draining condensate from a temperature regulated, steam operated heat exchanger. A buffer tank having a volume at least equal to that of the steam compartment is connected to the steam side of the heat exchanger, and a drain line extends from the bottom of the buffer tank to a condensate collection pipe located above the buffer tank. The drain pipe from the heat exchanger includes an air venting device and a control pipe having a non-return valve linking the top of the tank to the steam side of the heat exchanger. During low load operation of the heat exchanger, air from the top of the buffer tank can flow back to the steam compartment of the heat exchanger to equalize the pressures and permit drainage of the condensate even during low load conditions.