I have an Emerson media filter cabinet and it came with a MERV 8 White-Rodgers filter. It says to change it every 3 - 6 months. Do higher efficiency filters need changing less often? Would it be worth getting the MERV 11 filters?

We run our fan all the time to improve air circulation. When do I know it's time to change the filter? I read somewhere that you can't tell just by looking at it.

Thanks,
Mindy