Controlling HVAC system noise is essential to the quality of the listening environment in classrooms. The American National Standards Institute Standard S12.60-2002 — Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools calls for a maximum background sound level of 35 dBA for classrooms less than or equal to 20,000 ft³ (566 m³), and 40 dBA for classrooms that are greater than 20,000 ft³ These levels are much lower than previously recommended. Careful attention to the design, selection, and detailing of HVAC systems in schools is required to achieve these lower levels.