AutoCAD MEP

[#1]

hi, this might seem like a stupid question but i am just learning hvac on mep 2013 and the duct sizes sometimes come out in half sizes such as 13-1/2". i have set the flow rates on the diffusers and no matter what i try, i can't seem to get it to come out in straight sizes. am i missing a step?

[#2]

Sounds like you are using the duct size calculator.  If you are then you can set it to use whole inch increments.  This is done by using the USE CATALOG SIZES dropdown as shown in the picture below and selecting "1 inch increment".