This paper presents the results from the 1998 Interlaboratory Comparison Round Robin Testing. The fenestration thermal performance ratings (U-factors) were determined in accordance with NFRC 100 (1997), Procedures for Determining Fenestration Product U-factors and NFRC Test Procedure for Measuring the Steady-State Thermal Transmittance of Fenestration Systems (April 1997). A total of nine NFRC-accredited testing laboratories participated in the 1998 test round, and this paper presents the results. The round robin involved thermal performance tests on an aluminum-clad wood fixed window with high-performance glazing. Each participating laboratory received the same window product, which was shipped via common freight carrier. Each laboratory was directed to keep all test results confidential. The testing began in May and was completed in December of 1998. The results of each thermal test were reviewed and placed in a spreadsheet for analysis and data comparison. The expected results, or the relative position of data of any participating laboratory, was not divulged until all testing and data analysis was complete. Specific data regarding various measured and calculated performance values as required by the NFRC procedures and program documents are presented in this paper.

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