This paper presents analytical and numerical predictions of heat and pressure drop characteristics of a floor with the ventilating ducts. The experimental results are used to validate the models. An acceptable accuracy between the computational simulation and measured performance data is obtained. The analytical method is implemented as the computer program, which is a useful and accurate tool in designing heating system with underfloor air distribution. The bar chart of the design process and the diagrams for sizing the specific system of underfloor ventilation ducts are presented in the paper, too. (C) 2005 Elsevier B.V. All rights reserved.