The heat and mass transport model extended to describe silicon cluster formation in the gas phase is employed for a numerical analysis of SiC CVD in a commercial vertical rotating disc reactor. The growth rate is studied as a function of precursor flow rates varied in a wide range of values. It is found that the growth rate is limited by the gas mixture depletion in silicon atoms due to homogeneous nucleation. The secondary phase formation on the growing surface is analyzed. The SiC growth window depending on the precursor flow rates is calculated, and a significant effect of the homogeneous nucleation on the window width is found. The model predicts that the Si/C ratio on the wafer can considerably differ from that at the reactor inlet.