A three dimensional numerical investigation of steady laminar natural convection in vented enclosures is carried out.  A discrete flush-type heat source mounted on the substrate is used to simulate an electronic component.  Four different vent locations are investigated.  Combined natural convection in the air and conduction in the heat source, the substrate and the enclosure walls are solved for.  Solutions are obtained for Rayleigh numbers ranging from 10 (4) to 10 (6), different substrate thermal conductivity ratios and varied vent sizes.  The calculation domain is extended beyond the cubic enclosure in x, y and z directions.  Appropriate boundary conditions are prescribed on the extended computational domain.  The resulting flow and temperature patterns are discussed.  Also, the local and overall heat transfer and the substrate, in terms of Nusselt numbers and the surface temperatures, are presented to illustrate the vent effects.