To save energy through improved building operations requires determining frequent problems that have the largest savings potential. Most operations- and maintenance-related energy waste falls into four major categories. First, equipment scheduling – equipment runs when it is not needed. Second, outside air usage: economizer does not function optimally, or excessive outside air causes increased heating and/or mechanical cooling. Sometimes too little outdoor air compromises indoor air quality. This presentation will focus on these two topics, but will also address a third problem – sensor error:  erroneous sensor data causes increased heating, cooling, or equipment operation which can affect occupant comfort. The session also will include details on a fourth problem – simultaneous heating and cooling: the same air gets heated and cooled, or hot and cold air streams get mixed together to achieve the correct supply temperature. Gain information to help tune-up your building effectively.