Electric utilities are under pressure to reduce emissions and increase efficiency, and this means that coal-fired power plants must meet new challenges such as switching to coals for which the units were not designed. Ash deposition in coal-fired power plants reduces heat transfer and can cause the plant to be shut down. Ash deposits on convective heat transfer surfaces are generally removed mechanically by soot-blowers. On-line cleaning is practical as long as the ash deposits are not highly sintered. The sintering behavior of deposits is complex and depends on flue gas temperature, ash particle size, and ash composition. In this paper, a method is presented for estimating, for a specific coal, the maximum Rue gas inlet temperature that allows the convective heat exchanger to be cleaned using conventional means. The calculation was carried out for conditions that represent the steam superheater section of a conventional pulverized coal-fired power plant, and the results are consistent with observations from existing plants. The method was then applied to the design of a novel air heater being designed fur the Combustion 2000 HIPPS program.