This document, the 'THERM 2.1 NFRC Simulation Manual', discusses how to use THERM to model products for NFRC certified simulations and assumes that the user is already familiar with the THERM program. In order to learn how to use THERM, it is necessary to become familiar with the material in the THERM User's Manual. In general, this manual references the THERM User's Manual rather than repeating the information. If there is a conflict between the THERM User's Manual and the THERM 2.1 NFRC Simulation Manual, the THERM 2.1 NFRC Simulation Manual takes precedence. The CD that is included with the manual includes all sample files that are referenced in the manual as well as some additional samples.