The standard way of quantifying a noise level is with a decibel or dB(A) measurement. The lower the dB(A) level the quieter the system. Indoor units run from 19 dB(A) at low speeds to 49 dB(A) at high speeds (for reference, the quiet library has a noise level of 40 dB(A). Ductless mini-splits are not any louder than a standard AC unit. They are designed to be quiet and therefore ideal for living spaces and environments such as classrooms, libraries, theaters, healthcare facilities or places of worship.