The moisture content of paper will vary depending how it is stored. During printing, the paper is heated rapidly and warm, moist air will rise from the paper. When it encounters cooler air, water vapor or steam is produced. This is normal behavior and should not cause concern, the vapor will quickly dissipate and print quality will not be affected. You can minimize this occurrence by ensuring the machine is in a well-ventilated area, and paper is stored in a low humidity environment.