The dryout heat flux applicable to light water reactor fuel elements covered with porous deposits characterized by the presence of “steam channels,” or chimneys, is determined by the “wicking” or “choking” limit. The results of a study of these limits show that the dryout heat flux for thick, dense, or small particle size deposits is controlled by the wicking limit. In contrast, the choking limit is limiting for thin, highly porous, or large particle size deposits. The calculations also show that the choking limit results in dryout heat fluxes that are two to three times greater than dryout heat fluxes on clean surfaces.