An　experiment　has　been　performed　to　investigate　the　natural　convection　heat　transfer　coupled　with　the　effect　of　thermal　conduction　from　a　steel　plate　with　discrete　heat　sources.　Two　boundary　conditions,　with　constant　heating　flux　and　constant　heating　temperature,　were　obtained　by　controlling　the　heating　flux　or　temperature　of　the　heat　sources　mounted　on　the　back　of　the　plate.　The　heat　transfer　and　temperature　distribution　of　the　plate　were　measured　with　different　heating　spaces.　By　defining　the　average　heating　temperature　of　the　plate　as　the　characteristic　temperature,　simple　expressions　for　the　average　heat　transfer　are　correlated　from　the　experimental　data　as　a　function　of　the　relative　heating　space　and　Rayleigh　number.　The　error　is　5%　in　the　Rayleigh　number　range　from　5　x　10(8)　to　5　x　10(9).　(c)　2006　Elsevier　Ltd.　All　rights　reserved.