An air purifier should be placed in an area that is equal or less than the CADR rating. A device that can effectively purify air in rooms less than 250 sq. feet should not be placed in the heart of large houses. You should ensure that the purifier isn't blocked from either its intake or output by placing it in a room with a large number of people. This means that the purifier should be out in open and in an area with consistent airflow.