Solar Chimney is a potentially effective low carbon technique that uses solar energy to heat and cool buildings or to enhance ventilation. Proper design of a solar chimney requires a reliable model to estimate the airflow rate generated by the heat of solar irradiation. Existing analytical models ignore density variations either for the whole channel or across the channel gap. This paper presents a plume model based on energy balances and the thermal boundary theory and thus considered density variations in both horizontal and vertical directions. This plume model, expressed implicitly as a function of heat flux, can be solved easily through simple iterations. The performance of the model was verified by using experimental data in the literature. Results show that the plume model outperformed existing analytical models. Recognizing the challenges in airflow measurement, we suggest that further tests and calibrations of this plume model be done by using more concrete and accurate experimental data. Simple in form, the plume model has its potential in building simulation programs. (C) 2016 Elsevier Ltd. All rights reserved.