Abstract: An apparatus and method for measuring the air leakage rate of a structure, such as a building, for the purpose of assessing the need to add caulking, weatherstripping or the like to the building to minimize energy loss. The equipment includes a panel which may conveniently fit into a doorway or window frame of the building and seal the same against air leakage except for an air pathway passing through the panel. The pathway has a fan or the like for causing air to flow through the pathway, preferably from the inside to the outside to create a partial vacuum inside the building. Pressure sensors are provided to measure the partial vacuum and the air pressure inside the air pathway. From these measurements and a knowledge of the total internal volume of the building structure, the air leakage rate of the structure can be determined and expressed, for example, as a number of total volume changes per hour. The apparatus is portable and can be used for almost any building without structural modification.