One of the primary goals of the radiant heating and cooling community for the past two decades has been the fair and accurate comparison of radiant space conditioning systems with conventional forced air systems. The desire of the community was to give architects and engineers the ability to compare the energy consumption of different system types while requiring the systems to produce equivalent thermal environments. Unfortunately. radiant systems, though relatively simple in concept, are relatively complex from a modeling standpoint. A rigorous model must include fundamental laws of thermodynamics and properly account for heat transfer due to radiation, convection. and conduction. In addition. the model must do this in a Generic way within a program that is capable of modeling buildings of any size and type and their associated HVAC systems. Such challenges are not easily overcome and require careful attention to detail as well as a solid foundation from which to build. This paper summarizes a model which addresses these concerns and provides a radiant system model within a popular building energy simulation program. (C) 2004 Elsevier B.V. All rights reserved.