CIC's and vents

What determines the size of a vent in a CIC. Is it just how much room the shell has left after the guts are in there or does something else determine the size? Thanks, Howie:confused:

The vent size is determined by your loss. As a general rule, the more low frequency hearing you have, the larger the vent need to be.

It is of course also determined by the physical size of your ear, and the physical size of the components in the hearing aid.

Unless an aid has a very sophisticated anti-feedback system built in, there is also a reality that the larger the vent, the more likely the aid is to feedback. So sometimes one has to compromise the desired size a little based on a variety of these factors.