A method has been employed to augment the forced convection to ambient air from a horizontal rectangular plate with its upper surface mounted with transverse (to the mean air-flow) rectangular ribs, which are uniformly spaced and heated. The enhancement has been achieved by drilling uniformly-spaced holes in the base plate between consecutive ribs. The steady-state effects of varying the penetration ratio, [beta], (i.e. of the total cross-sectional areas of the holes to the whole base-plate area between consecutive ribs), diameter of the hole, d, ratio of channel's height to rib's common height, H/B, and Reynolds number, Rec, of the air-flow on the rate of forced convection from the rectangular plate were investigated experimentally for both laminar and turbulent flows over the ribs. Heat-transfer measurements were obtained for the ranges: 500[less-than-or-equals, slant]Rec[less-than-or-equals, slant]19,000; 4[less-than-or-equals, slant]H/B[less-than-or-equals, slant]10 and 0.05[less-than-or-equals, slant][beta][less-than-or-equals, slant]0.20. The following correlation applied for the prediction of the average heat-transfer coefficient for this heat-transfer system (i.e. as contained in the wind-tunnel): To achieve the maximum heat-transfer performance with this type of heat exchanger--for a specified application in which the degree of inhibition experienced by the air in flowing through the holes is known--optimised choices of the location, diameter and number of holes, as well as for the materials of the ribs and base, have to be made.