This paper considers the influence of heat exchangers to the efficiency of a household refrigerating system. A steady state mathematical model is used to compare three most commonly used heat exchanger designs. For each design, an optimal inner diameter of the heat exchanger, subject to the compressor's capacity and the heat exchanger's length is found. The influence of operating conditions, such as condensation and evaporation temperatures, superheat in the evaporator and sub-cooling in the condenser, to optimal dimensions of the heat exchanger is also analyzed in the paper. Presented guidelines and recommendations can be used for design and modernization of household refrigerators and freezers. (C) 2003 Elsevier Ltd and IIR. All rights reserved.