The objective of this work is to design a new system for heating water from the waste heat of the exhaust gas of a power generator. It consists mainly on installing a lamellar heat exchanger to recover the wasted heat of a diesel engine. For thus, we have also developed a numerical simulation to study the heat following the flow of water and exhaust gas in the proposed interchange. The numerical model considered is based on the resolution of the Navier-Stokes equations in conjunction with modified k-epsilon turbulence model. These equations were solved by a finite volume discretization method. We studied four types of diffusers using different inclined angle and we are particularly interested to visualize the temperature, the velocity, the total pressure, the dynamic pressure, the vorticity, the turbulent kinetic energy, the turbulent dissipation rate and the turbulent viscosity. (C) 2015 Elsevier Ltd. All rights reserved.