A cabinet for housing telecommunications equipment in outdoor locations includes an enclosure for containing the telecommunications equipment. A subrack is mounted within the enclosure. A duct directs ambient air from outside the cabinet to the subrack. The duct includes an inlet disposed in a lower portion of the cabinet and a subrack inlet plenum disposed immediately below the subrack. A subrack exit plenum is disposed above the electronic subrack for exhausting air heated by the electronics equipment. A fan draws ambient air into the inlet through the duct into the subrack inlet plenum, through the electronic subrack into the subrack exit plenum, and out of the enclosure through the subrack exhaust plenum. A heater is provided for heating inlet air when ambient temperatures are low. The fan and heater are controlled by a thermal controller. At low ambient temperatures, the air flow is maintained constant by the fans and power to the heater is varied to maintain the subrack inlet temperature constant. At moderate temperatures, the heating element is turned off and the fan speed is varied up to the maximum fan speed. At high temperatures, the fans operate at full speed to maintain maximum air flow.