CPV code 71321400 designates Ventilation consultancy services in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
71321400 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 71321000 (Engineering design services for mechanical and electrical installations for buildings).