Having key advantages of higher heat transfer and compact size, helical tubes have been commonly adopted in major industry applications especially heat exchangers and chemical reactors. On top of their encouraging industrial adoption, helical tubes have attracted significant attention from researchers worldwide due to its complex flow behavior. This study addresses the flow characteristic and heat transfer performance of a laminar flow inside helical tubes with various curvature diameters. The laminar flow of a Newtonian fluid inside helical tubes is investigated by utilizing a computational fluid dynamics approach. Both constant wall temperature and constant wall heat flux conditions are examined. Their heat transfer performance is numerically evaluated and compared by utilizing the concept of Figure of Merit (FoM). In addition, the inefficiency of the helical tube is analyzed by utilizing entropy generation analysis. The results indicate that heat transfer performance increases as the curvature radius decreases. Albeit higher pressure drop, helical coil generate lower entropy than straight tube. © 2017 The Author(s).