We propose a method of finding the transient temperature variation in an insulated cooking device. We also report a means of optimising the thickness of insulation. The cooking device is a double walled cylindrical vessel with spacing of 5–20 mm between the vertical walls (width) and spacing of 560 or 870 mm between top and bottom surfaces (height). The height to width ratio (H/L) is between 28 and 174 and Rayleigh number (Ra) is between 907 and 2.61 × 105. First, an energy balance for the cooking device is established. A correlation is developed to predict the heat transfer coefficient (HTC) as a function of Ra and H/L. The method developed for finding the transient variation in temperature has been tested on two cooking device volumes: 120 and 700 lit. Using the optimised parameters, a reduction in heat loss of 22% and 30%, respectively, is observed
