An experimental program was initiated to determine the friction factor in a straight duct and the loss coefficient of either a single elbow or two elbows places in close proximity. The tests were performed in accordance with ANSI/ASHRAE standard 120-1999. Loss coefficients C were measured for six kinds of single elbows. Likewise , identical pairs of elbows were considered in the close-coupled elbow experiments. For long separation lengths, the loss coefficient for two close-coupled elbows approached to within approximately 10 % of the value of 2*C for a single elbow, for most cases considered in this study. The single-elbow data were also compared with those published in the 2002 Ashrae Duct Fitting Database.