Most often with ALL pianos, the keys will sometimes stick. The comments on Humidity are the most correct.
1) First, do NOT EVER place your piano close to doors to the outside.
2) Also keep away from vents in your studio or home. if you don't have a choice, Close the vents
3) Mostly with humidity being of low levels I would suggest a contraption called a "Dampp Chaser" this will humidifiy your piano.
4) Sometimes damppchasers come as humidifiers and/or dehumidifiers, so if you live in a humid area, I would suggest to get a Dampp Chaser that is a dehumidifier.
DO NOT EVER USE HUMIDIFIER IN HIGH HUMIDITY
NEVER USE DEHUMIDIFIER IN LOW HUMIDITY ENVIRONMENTS...
THIS could have SERIOUS, Expensive, and sometimes even IRREPARABLE Consequences. Always buy from a Professional, and READ ALL DIRECTIONS OF USE AND OWNERS MANUAL