U.S. Air Force Staff Sgts. Will Davey and Chris Rundell, Heating Ventilation and Air Conditioning (HVAC) craftsmen assigned to the 633rd Civil Engineer Squadron, loosen bolts on an HVAC system at Langley Air Force Base, Va., Jan. 5, 2016. HVAC craftsmen install, maintain, repair and operate heating plants, systems and equipment. (U.S. Air Force by Staff Sgt. J.D. Strong II)