Very few loss coefficients are available in ASHRAE databases for flat oval duct fittings. The use of CFD instead of lab experiments to determine loss coefficients for duct fitting has been validated using comparisons to existing data for round and flat oval duct fittings. Experimental data for a variety of fitting geometries and flow rates were all within 20% of CFD results. Following the benchmark, loss coefficients for flat oval mitered 90° fittings and a flat oval three gore 45° fitting were determined. For future work, surface roughness will be added to the CFD model to improve accuracy, and a wider range of fittings will be evaluated.