AC register box openings

[Michael Vasquez]

I had a question on the size of the duct board cutouts at register boxes. The duct work throughout the attic was constructed of duct board. Some of the cutouts visible through the vents were small; not the size of the register box. Should these openings be large enough for proper air distribution? Thanks

[Jim Luttrall]

Should these openings be large enough for proper air distribution?
The answer to your "stated" question is yes, but I think you really want to know if the cutout openings should be the same size as the registers for proper air flow.
The answer to that question is "it depends or not necessarily."
The cutouts "can" be used to balance the air flow like an adjustable damper would in a traditional duct system. Then the grills are larger to make the system quieter.
Bottom line, I would not be concerned unless there was an apparent lack of airflow for the room the vent(s) were serving.