Circulation in the industrial boiler is the continuous supply of water to the boiler heated tubes in order to sustain steady steam output without overheating tubes. Adequate circulation occurs when there is sufficient flow of water into tubes for adequate cooling. In the natural circulation industrial boiler system the rate of flow in the circulation system is governed by flow resistances and differences in density between downcomer tube circuits and heated riser circuits. Control of these resistances allows adequate flow of water to parallel circuits. Adequate water flow through the boiler's heat-absorbing circuits is necessary to cool the tubes. To insure proper boiler circulation, a simple, clear, and comprehensive approach is described in this article covering all aspects in boiler circulation analysis. The analysis details all boiler circulation circuits, explaining all forces imposed on them, including thermosyphon as well as friction forces.