I would probably change the oil the first time at about three hours of good cycling. After the oil is changed the first time,you should probably change it every couple months if you use it pretty heavy,if just on occasional use change once a summer,just to keep fresh oil in it.Just remember it doesn't have a pressure lubed system so as long as you use like a pennzoil 5-30 or an equivalent non-detergent oil,you should have no trouble with humidity . The humidity or temp. changes don't seem to effect them much ,so as long as its not -20 or -30 below you should be fine.Enjoy your compressor!!