Recent ecological and political developments have created an increased focus on sustainable energy sources. The purpose of this paper is to examine a passive ventilation device, the windvent, and evaluate its potential against current British Standards BS5952:1991 [British Standards, Ventilation principles and designing for natural ventilation, BS5925:1991 (1991)] recommended fresh air delivery rates. The results provide useful information for both engineers and architects when examining ways to reduce new and existing buildings running costs, and conform to new legislation. Numerical analysis is carried out using a commercial Computational Fluid Dynamics (CFD) code, to investigate the effect of various external wind velocities (1-5 m/s) and directions (concurrent and counter current) on the device performance. The results show that the windvent is capable of providing recommended rates of fresh air supply even at relatively low incident wind velocities. The performance indications show that the device warrants further analysis and provides a sustainable alternative ventilation system. (C) 2008 Elsevier B.V. All rights reserved.