A cooling device for rack mount equipment comprises an extensible side duct, open on its inner and rear-facing sides which redirects warm exhaust air exiting vents in the side of a chassis towards the rear of an enclosure holding the chassis. An apparatus incorporating the cooling device may be installed in a rack with the extensible side duct in a retracted position. The extensible side duct may extend under the influence of air pressure, forming a plenum in fluid communication with the interior of a chassis on which it is mounted such that warm air exiting the chassis is collected in the plenum formed by the extensible side duct and directed out towards the rear of the chassis. Use of the apparatus permits conventional front-to-back cooling airflow patterns to be maintained even with chassis having side exhaust vents.