The effect of jet-to-jet spacing on the local Nusselt number for confined circular air jets vertically impinging on a flat plate is investigated. Five jets in equilaterally staggered arrays are considered. The surface heat flux on the plate is 1500 W m(-2). The jet diameter is 3 mm. Three different jet Reynolds numbers (Re = 10,000, 20,000 and 30,000) are individually considered. The influence of jet-to-jet spacing, Re and jet height on the stagnation Nusselt number of the center jet is experimentally investigated. An optimum ratio of jet-to-jet spacing to jet diameter, (s/d)(opt,) is obtained. The existence of the (s/d)(opt) is attributed to jet interference before impingement and/or formation of jet fountain between two adjacent jets. The stagnation Nusselt number is correlated as a function of Re, s/d and H/d.