Channeling energy affects both the living and the undead at the same time. Releasing a burst of positive energy will heal all living creatures in its radius and damage all undead. Likewise, channeling negative energy will damage all living creatures and heal all undead creatures in its radius.
Deities and Clerics
Unless otherwise stated, evil deities and only evil deities grant the ability to channel negative energy. All other deities grant the ability to channel positive energy.
Neutral clerics do not select whether they will channel positive or negative energy. Instead, they channel based on the alignment of their deity.