Chi Kung and breathing

You are correct.
Sometimes it is out of nose, and sometimes it is out of the mouth.

Breathing out the mouth is better for detoxification purposes,
which is why we breathe the sound out the mouth when we do the
Six Healing Sounds. Toxins are more effectively eliminated,
stuck qi, stale air, etc.

However, you release a lot of qi when you do this, i.e. detoxify.

If you breathe out the nose while keeping your mouth shut,
you retain more of your qi /energy. By harvesting qi from the air,
and by retaining your energy supply in this way, you can build up your energy.

To summarize:
If you are trying to detoxify, you should
breathe out the mouth. If you are trying to “build-up”, you
should keep your mouth closed and breathe out the nose.

Neither one is exclusively correct. It is good to detoxify
from time-to-time. Lots of environmental, emotional, etc.
toxins accumulate over time and can lead to disease. It is
good to flush those out. But you can’t detoxify all the time, as
it fatigues your body. Building-up is consequently also important.

Balance is key.

Qi,
Steven

Ondine’s curse, also called congenital central hypoventilation syndrome (CCHS) or primary alveolar hypoventilation, is a respiratory disorder that is fatal if untreated. Persons afflicted with Ondine’s curse classically suffer from respiratory arrest during sleep.
-http://en.wikipedia.org/wiki/Ondine’s_curse

Sorry, but in my opinion it would be beneficial if one is serious with one’s practice to add carefully more varied program of breathing exercises.

So for example nadi shodhana pranayama (alternating nostril breathing), uyyaji pranayama, sheetali and sheetkari pranayama etc. could be used.

None of these should be particularly dangerous unless one starts too violent retention of the breath too early.

But whatever one is doing one should not, in my opinion, be too schematic with one’s conceptions, but try to develop more subtle perceptions and as a result better understanding what one is doing and why.

HOWDY