Abstract Heat transfer enhancement and pressure loss of a fin-and-tube heat exchanger with rectangular winglet pairs has been numerically investigated by solving the conservation equations of mass, momentum and energy. The flow is assumed to be laminar at different Reynolds numbers. The winglets are placed in common flow up configuration which increases the heat transfer in the wake region of the tube. It was found from the numerical investigation the rate of heat transfer is increasing with number of winglets. It was also found that the placement of winglets near the central tube is more effective in transferring heat compared to entrance and exit of the heat exchanger. Keeping other parameters fixed it was found from the numerical experiment that the heat transfer performance was increasing significantly with the attack angle (β) of winglets. There also exists an optimum stream wise distance (ΔX) for placement of winglets for which the heat transfer is found to be highest. An optimum value of span wise distance (ΔY) could be decided where the heat transfer to the fluid was found to be maximum.