In this work steady flow of fluid in shell and coiled tube heat exchangers has been simulated then analyzed. Effect of pitch, coil’s diameter, tube’s diameter, shell’s diameter, coil’s height, shell’s height and Reynolds number on the friction factor of coil side has been investigated using numerical method. Forty cases have been analyzed in numerical work. The working fluid of both sides is water which its viscosity and thermal conductivity were assumed to be dependent on temperature. The standard K-έ model was used for turbulence. Results indicate the diameter of the coil is the most effective geometrical parameter on the friction factor of the coil side so that by remaining other parameters constant, if the coil’s diameter increases 60%, the friction factor will decrease 30.6%. Also by remaining other parameters constant if the tube’s diameter is doubled the friction factor of the coil side will increase 16.5%, if the shell’s diameter is doubled the friction factor of the coil side will increase 11.7% while the effect of other geometrical parameters on the friction factor of the coil side is much less than the effect of coil’s diameter, tube’s diameter and shell’s height. Also a correlation has been proposed for prediction of the friction factor of the coil side that contains the effect of all defined geometrical parameters in addition to Reynolds number. This correlation is applicable for wide range of Reynolds number (2700< Re< 38000) and has been compared with the correlations proposed in previous works.