Abstract In this study, combined effects of length and heat flux of the coil as well as the effects of temperature dependence of thermophysical properties on entropy generation rates and optimal operation of uniformly heated helical coils with laminar forced convection have been analyzed analytically. For these purposes, comprehensive analytical formulas, which could be used for any duct shape and flow regime, are derived for thermal, frictional, and total entropy generation rates, and the effects of involved parameters on the entropy generation rates are examined for laminar forced flow of water through uniformly heated helical coils. Then, using the minimal entropy generation principle, the inlet Reynolds number is optimized for various values of the involved parameters, and some correlations are proposed for optimal values of this parameter which extend and modify the existing correlations of water. It is found that the entropy generation rates are highly dependent on the combined effects of length and heat flux of the coil, introduced by the parameter η C , and temperature dependence of thermophysical properties, such that all of them noticeably augment with increase in η C and the inlet temperature.