In this paper, numerical study of the gas flow velocity space is presented in a convection type reflow oven. Convection reflow ovens usually apply the nozzle-matrix heater system which generates numerous gas streams perpendicularly to surface of the soldered assembly. The ovens are divided into zones; every zone contains an upper and a lower nozzle-matrix. The temperature can be independently controlled in each zone; however the velocity of the influent streams is usually fixed. The gas flow velocity space is one of the most important parameter of the local heat transfer coefficient in the oven. The gas flow space cannot be examined by classical experimental methods due to the extreme circumstances in the reflow oven. Therefore the effect of the soldered assembly, the different component sizes, the position of the conveyor belt and the vent hood between the zones on the gas flow velocity space was studied by CFD simulations. These results can be useful during the overview of the actual assembly design and manufacturing rules. (C) 2013 Elsevier Ltd. All rights reserved.