This new line of heaters uses direct steam injection to rapidly and accurately heat water and water-based slurries in a variety of process applications, such as boiler feedwater preheating, heating fibrous slurries for pulp stock and biomass treatment, paper-starch processing, sanitization and tank cleaning, anaerobic treatment of organic waste, and others. By using all of the sensible and latent heat of steam to heat the fluid, these systems can provide heating equal to that of an indirect heat exchanger with 20–30% less energy consumption.