Senior Airmen Jose Hinojasa (left) and David McMillen, 28th Civil Engineer Squadron heating, ventilation and air conditioning technicians, install an exhaust stack into a new boiler system in the base Exchange at Ellsworth Air Force Base, S.D., Aug. 15, 2013. HVAC personnel work hard to provide suitable working conditions for more than 3,500 base personnel. (U.S. Air Force photo by Airman 1st Class Zachary Hada/Released)