An air handling unit for a data center, a data center comprising such a unit, a method of operating such a unit and a method of cooling IT equipment in a data center using such a unit is disclosed. An indirect air handling unit (IDAHU) (101) for a data center comprises an external air flow path (102) arranged to be in fluid communication with air outside the data center; an internal air flow path (103) arranged to be in fluid communication with air inside the data center, wherein the external air flow path (102) is separated from the internal air flow path (103); and a plurality of heat tube panels (106).