Helical Coil Heat Exchanger (HCHE) is a type of heat exchanger which has a shell called annulus and inside it, there is a helical coil. It occupies less space and provides more surface area for effective heat transfer as compared to shell and tube heat exchanger. HCHEs find their use in compact nuclear reactors, e.g., Small Modular Reactors (SMR). With the help of our project work, the industry will become familiar with the benefits of HCHE. That’s why, HCHE is designed by taking essential parameters like heat load, inlet and exit temperatures of both coil and the annulus and the velocity inside the coil from industry (Altern Energy Ltd). In the present work, an HCHE with a heat load of 25kW is designed and developed. Pressurized hot fluid in the annulus side at 106 Pa is used as a heating medium that transfers heat with cold fluid at 105 Pa in counterflow configuration. Both inlet and outlet temperatures have been taken from the power plant. Stainless Steel material is chosen with grade 304 (SS304) because of its good anti-corrosion characteristics and ease of availability. Water is used as a working and primary fluid. For this purpose, a helical coil of a 19 mm pitch with an average helix diameter of 305 mm is used. Temperature and flow rate of water is varied in the annulus side and helical coil, and the heat transfer characteristics of the helical coil are investigated. The design of the heat exchanger in current work provides a full range of data on helical coil heat exchanger outlet conditions as a function of input parameters. The input parameters include the amount of constant heat flux, flow rate and temperature of primary and working fluids. Results have shown the fact that there is a rise in overall heat transfer coefficient and heat transfer rate when the mass flow rate of cold water in coil or hot water in the annulus is increased. It is found that the helical coil is good in terms of heat transfer.