The purpose of this recommendation is to provide a comprehensive overview of features that determine highly efficient operation and correct service of air handling units, which in other words are a measure of the AHU quality. The document addresses a wide range of aspects, such as properties of the casing and individual components, energy efficiency and controls requirements, maintainability, and the content of technical documentation. Detailed recommendations based on the expertise and many years of experience of Eurovent members indicate what distinguishes a good air handling unit. The guidelines in this document are intended to help investors, designers and end-users to assess whether the unit meets all practical expectations and requirements.