Developments in heating, transportation and power sectors facilitate the creation of an integrated power and heat system, which can provided better solutions compared to operating each system individually. The scope of this paper is to provide a detailed procedure on the modeling of a modern heat and power integrated system. Two methods are being investigated: a sequential procedure and a merged procedure. Comparisons are made in terms of accuracy and computational cost to highlight pros and cons of each method. Simulations results are obtained with MATLAB software and validated through commercial software PSS SINCAL and DIgSILENT PowerFactory.