While at PFS today, the GM and I entered an arguement about Purifying Channel
You can choose whom to affect when you channel energy.
Prerequisite: Cha 13, channel energy class feature.
Benefit: When you channel energy, you can choose a number of targets in the area up to your Charisma modifier. These targets are not affected by your channeled energy.
Normal: All targets in a 30-foot burst are affected when you channel energy. You can only choose whether or not you are affected.
Your healing energy also damages your enemies.
Prerequisites: Cha 15, Selective Channeling, channel energy class feature.
Benefit: When you channel positive energy to heal, one creature that you exclude from your channeling takes an amount of fire damage equal to the die result you roll for healing, and is dazzled for 1 round by the light of these flames. A successful saving throw against your channel energy halves the fire damage and negates the dazzled effect.
Can I use the damaging effect from Purifying Channel on constructs?
My GM was arguing that because it's a channel, it can only effect living targets, not constructs. Likewise, he said that constructs aren't legal targets for channels, so you can't exclude them via Selective Channeling, therefore the damage can't be applied to constructs.
I was arguing that it should effect constructs because the energy in question is no longer positive energy, but fire. Likewise, while constructs are uneffected by channels, they're still targets within the channel's area and thus can be excluded and set on fire with Purifying Channel.
I'm going to have to agree with your DM; sorry. The text for Channel Energy states that 'This energy can be used to cause or heal damage, depending on the type of energy channeled and the creatures targeted', from which I infer that channeling positive energy to heal targets only living creatures, so constructs are not valid choices for Selective Channeling (they are not 'a target in the area' because they are not a target).