Rear door heat exchanger

A rear door heat exchanger, or RDHx, is a chilled water coil on the back of a server rack that cools exhaust air before it reaches the room. Vertiv calls its version a cooling door. Passive doors use only the airflow from the servers' own fans. Active doors add built-in fans that pull exhaust air through the coil, supporting higher heat loads at the cost of fan power.

Vertiv's Liebert DCD passive door is rated up to 35 kW in the DCD35 and up to 50 kW in the DCD50, and Vertiv says an active door may be recommended at 50 kW depending on conditions. Its data sheet rates the DCD35, DCD47 and DCD50 at 35, 47 and 50 kW, the DCD47 as an active model only, with 21 °C room air and 12 °C entering water. The active fan module draws up to 980 W on the DCD35 and 1,185 W on the DCD50.

Compare doors only at the same rating conditions, since capacity depends on entering water temperature and rack airflow. A passive door relies on server fans, so check the installed hardware's airflow before choosing passive over active.

Sources

Last verified October 30, 2026.