Air preheater is one of key elements in today's energy-saving technology. Its performance deeply depends on the underlying configuration for heat transfer. In this paper, the pressure drop and heat transfer characteristics of a high-efficiency plate-fin structure used in an air preheater are experimentally investigated under a large variety of conditions. In particular, the critical Reynolds number for the conversion from laminar to turbulent flow in the system is obtained, and the heat transfer coefficients in the gas and air sides of the heat exchanger are successfully separated from the overall heat transfer coefficient using Genetic Algorithm method. The main conclusions drawn from this work will be helpful for future development and design of a high-efficiency heat preheater involving plate-fin structures. (C) 2011 Elsevier Ltd. All rights reserved.