A simple approach and practicable prediction method of transmission heat loss would significantly benefit to the comprehensive applications in the hot water system design. This paper proposes an empirical prediction method and defines new parameters to simplify the equation to calculate energy consumption in hot water system. The temperature drop mechanism is established by empirical approach to replace multiple factors in the theoretical heat loss equation developed in air conditional technology. As a result, it is proved that the proposed empirical prediction approximates to the results of theoretical calculation in the range for practical applications. (C) 2006 Elsevier B.V. All rights reserved.