To design a compact centrifugal fan with parallel wall volute, the ratio between the impeller exit width (B2) and volute width (B5) is kept high. In the present study, a detailed numerical simulation of parallel wall volutes for backward curved centrifugal blower with different (B5/B2) ratios (4 and 5) is carried out. These simulations are done for varying mass flow rates. By increasing the ratio from 4 to 5, the material required by the volute can be reduced by 15%. The analysis of the flow field shows that an increase in the B5/B2 ratio causes a slight decrease in the pressure ratio and efficiency at higher mass flow rates. At the outlet of the impeller, higher ratio volute generates a more uniform flow distribution which reduces the structural load on the impeller. Copyright © 2012 by ASME.