Mathematical heat transfer equations for finned double pipe heat exchangers based on experimental work carried out in the 1970s can be programmed in a spreadsheet for repetitive use. Thus avoiding CFD analysis which can be time consuming and costly. However, it is important that such mathematical equations be evaluated for their accuracy. This paper uses CFD methods in evaluating the accuracy of mathematical equations. Several models were created with varying; geometry, flue gas entry temperature, and flow rates. The analysis should provide designers and manufacturers a judgment on the expected level of accuracy when using mathematical modelling methodology. This paper simultaneously identifies best practices in carrying out such CFD analysis. Methodology; CFD software was used to simulate different models. Results were tabulated and graphically presented. The investigated mathematical equations were programmed in a spreadsheet, for data entry. Results and analysis; data obtained from the two methods were compared and differences were recorded. Discussions were included explaining the possible reasons for the deviations that surfaced between the two methodologies. Conclusions; this analysis has shown that although mathematical equations are effective and simple tools in producing results, the results may not reflect the actual physical conditions. The analysis showed that the exhaust gas temperature outlet of a double pipe heat exchanger is actually higher than what were calculated using mathematical equations, and therefore, more heat energy is available for recapturing. k-epsilon RNG turbulence model was found to be the most suitable method in analyzing heat transfer in a finned double pipe heat exchanger.