Increasing the use of natural daylight for lighting purposes in buildings may offer savings in total building energy consumption. One technique is the use of lightpipes that can not only bring light into otherwise inaccessible or dimly lit places, but also improve the internal environment without generating excessive heat. This investigation aims to develop a unit combining light pipe technology and passive stack ventilation by utilising the light pipe as an exhaust stack. The performance of two light pipes with diameters of 215 mm and 2.2 m in length, have been continuously monitored in two separate environmental chambers situated outdoors. Measurement of low velocity airflow rates and natural stack ventilation through the test chambers has been carried out using the constant injection tracer-gas method. The results show a good correlation between solar altitude/time of day, internal lux values and the external lux values. Temperature inside the chambers was controlled and stayed at approximately 20°C. Typical air change rate through the passive stack is about 8 air changes per hour in Winter. Computational Fluid Dynamics (CFD) has been used to investigate the simulated performance of the passive stack ventilation through the integrated system. An identical chamber with ventilation stack was created computationally in three dimensions and simulated with typical boundary conditions and operating conditions from experimental results. The simulation results showed that CFD can be a useful tool for the design of passive stack systems. The experimental results show that lightpipes are proficient devices for introducing daylight into buildings and reducing energy costs. An analysis has shown that the use of light pipes can lead to savings in electricity usage of up to 20 – 30 %.