A large number of potential noise sources appear in building HVAC&R systems installation. Noise generated in central plant can be confined within installation rooms, located in the basement or on top of a building, and be treated properly. But ductwork still remains as an effective sound transmission path within a building, inside which turbulent flow is a source of broadband noise. Air distribution system including fan, straight pipe, elbow, branch take-off, grilles, diffusers, terminal boxes, manifolds, etc. should be designed carefully with acoustical calculation to minimize sound transmissions. However, the methods for ductwork noise regeneration and attenuation calculation recommended by Practical HVAC Design Manual, China (2008) (PDM) [5] and ASHRAE Handbook (2015) (AAH) [1] are not fully identical. Therefore, these two methods are compared and a ductwork is taken to exemplify their differences. Airflow noise through fan, straight pipe, elbow, branch take-off, etc. and noise attenuations of these components are calculated in terms of two methods, respectively. It is found that the method used in China is mainly based on empirical formulae, with some figures and tables. Few empirical formulae are given in related chapters in AAH, but mainly figure and table based. Result indicates that the airflow noise of elbow as well as noise attenuations of elbow, branch take-off from two methods are almost identical, while the values of airflow noise of branch take-off and noise attenuations through straight duct at low frequencies are obviously different. The differences even reach 26dB and 1.74dB for the case studied. We referred to the method provided in CIBSE Guide B4 (2016) [3] and found the airflow noise of branch take-off calculated by method of PDM is more closed to the measured values, but the number of cases measured is very limited. Thus, a lot more research should be carried out in this direction to better the calculation method. And the method to determine noise attenuation through straight duct used in China should be updated and that used in USA can also be better gradually.