Tracer gas measurements of the total ventilation rate were made in an unoccupied test house in which an exhaust fan was cycled on and off for four-hour intervals. The exhaust was operated at a flow rate equivalent to 0.85 air changes per hour, and the house leakage configuration - varied by window opening and flue blocking to produce natural infiltration rates - was from 0.1 to 0.5 air changes per hour. Several simple theoretical models for combining fan and natural ventilation flows were compared to the measured data. Direct linear addition of the exhaust and natural flow rates was found to give a superior estimate of the total flow compared to other formulations, including the quadrature superposition recommended in ASHRAE Fundamentals (ASHRAE 1985).

Units: SI