This paper describes the contents of two technical publications by the CIBSE Mechanical ventilation Task Group. The first, provides information on air leakage testing in order to produce 'airtight' buildings for energy efficiency and better ventilation control. The second, describes the main factors associated with the design of efficient mechanical ventilation systems. Both form part of the Task Groups strategy, which is to promote energy efficient and effective ventilation design. The paper discusses the main features of the technical notes.