CTHE is a simple but powerful tool for the thermodynamical design and rating of a concentric tube heat exchanger or a coaxial heat exchanger. It can extimate the capacity of the exchanger and it can evaluate the required surface. CTHE allows the use of several common liquids, gases and refrigerants, plus user defined fluid. The fluid database is the best available. The current release is dedicated to the single-phase thermal exchange (liquid or gas/vapor).