In this study, thermal aspects, e.g. convective heat transfer coefficients were evaluated and modelled in open and greenhouse pond systems (natural convection). Values of the constants C and n were determined by linear regression analysis from the experimental data. It was observed that the ranges of the convective heat transfer coefficient were strongly dependent upon D/H (Diameter/Height) ratio of the container. It was also observed that the uninsulated container 5 (D/H = 5.240) and the insulated container 1 (D/H = 0.196) indicate minimum and maximum convective heat transfer coefficient in winter and summer months, respectively. Predicted and experimental values of convective heat transfer coefficients, verified in terms of root mean square of percent deviation, correlation coefficient and error bars (+/- SD), exhibit fair agreement. The model has been validated for the composite climate of New Delhi. Copyright (c) 2006 John Wiley & Sons, Ltd.