Heat recovery systems play an important role in waste to energy and biomass processing. An efficient approach that follows a recommended hierarchy in design, process as a whole (e.g., incineration) -> subsystem of the process (e.g., heat recovery system) -> equipment (e.g., air pre-heater), is shown. Important factors have to be taken into consideration in processes for incineration (combustion of biomass), especially available energy, specific features of hot process fluid (flue gas), type of waste/biomass, fouling, and environmental impact. A combination of intuitive design, know-how, and a sophisticated approach based on up-to-date computational tools is shown. Some novel types of heat exchangers (e.g., air preheaters for high- and low-temperature applications, heat recovery steam generators and/or heaters, and those for specific applications) that can be substituted for conventional ones are presented. An improved or even optimum design of heat exchangers requires computational support in the following areas: a simulation based on energy and mass balance, the thermal and hydraulic calculation of heat exchangers, a CFD (computational fluid dynamics) approach, optimization, and heat integration. Some examples are presented. An approach that ranges from an idea to an industrial application is demonstrated on the novel design of integrated compact equipment (combustion chamber installed inside heat exchanger) for the thermal treatment of waste gases, including heat recovery. This approach involves simulation for obtaining basic process parameters, thermal and hydraulic calculations, design of experimental facility, the manufacture of the equipment and building of this facility, operation and functionality testing, data acquisition for validating and improving the CFD model, and the utilization of feedback from industrial applications.