This paper experimentally investigates the performance of an absorber tube with heat transfer enhancer in solar flat plate water heater. The objective of the work is to increase the convective heat transfer by reducing the cross sectional area between the absorbing fluid and inner wall of the tube. The heat transfer enhancers are frictionally engaged with the inner side of the tube wall, and it is kept in the axial flow direction of the fluid flow path. Two types of heat transfer enhancers, namely, rod heat transfer enhancer and tube heat transfer enhancer, are used herein and compared with each other. The efficiency, heat transfer coefficient and pumping power for flat plate solar collector were analyzed, and it was found that, the rod heat transfer enhancer provides higher heat transfer with a small increase in pumping power than tube heat transfer enhancer and plain tube flat plate solar collector. The maximum increase in pumping power is 1.081 and 1.044 times higher for rod and tube heat transfer enhancers respectively, compared to plain tube solar collector. © 2016