This document gives recommendations on dimensions of ducts with circular and rectangular cross selections. The previous edition published in 1993, based on various national manufacturing or contracting standards, was used as a basic document for the preparation of the European Standards in the CEN/TC 156. This second edition of the Eurovent Recommendation 2/3 is in full accordance with European Standards pr EN 1505 and pr EN 1506. This document is available in English.