This electronic document summarizes HTRI calculation methods, provides design recommendations, and offers practical design tips. Topics covered include basic methods for single-phase pressure drop and heat transfer, condensation, boiling, two-phase flow, fouling, flow-induced vibration, and design guidelines for shell-and-tube, air-cooled, and non-tubular exchangers. This publication provides the basis for understanding HTRI software results and contains references to research reports for detailed study. The Design Manual is the comprehensive reference for HTRI’s latest research-based thermal design recommendations for all types of heat exchangers.