In this study, a focus on geometry & elements is taking place with open expansion tanks (OETs) to reduce the energy loss in the system. A new model based on the inlet and outlet flow control in the tank is developed by a semi-spiral coil. A fully numerical comparison of the proposed new OET and the conventional system is done in assistance with Computational Fluid Dynamic (CFD) modeling that has been utilized by QuickerSim CFD toolbox. In order to approve the data, an experimental set up was installed in the laboratory, which includes: three types of OETs (conventional, optimized twin container, and optimized by the coil). Finally, the economic analysis of the new design tank has been performed. The Net Present Value (NPV) in all the three scenarios (international, without subsidy and with subsidy) for optimized models is more than zero and Internal Rate of Return (IRR) is concluded 38%, 113.3% & 303%, respectively. Furthermore, the value of the Simple Payback (SPB) is half a year accordingly in the international energy price calculation based scenario. The results demonstrate the proposed OET that uses a coil, avoids the energy losses as much as possible. As an overall achievement, the energy losses in the OET with the coil are reduced in the range of 80% to 95%. Additionally, replacement of the conventional models by the new proposed design results in the annual energy saving of 857.1 cubic meters of natural gas per household.