Hellfire Warlock hellfire infusion question

[Faolin]

When I reach 2nd level of hellfire Warlock, do I need to select an energy type for energy substitution? All the ability description says is that I can apply energy substitution, nothing about what type of energy I substitute with.

[Thurbane]

From my reading, you can pick whatever type of Energy Substitution you like, each time you use the ability.

[Darrin]

"Special: You can gain this feat multiple times, choosing a different type of energy each time."

Based on this text, I would say that you have to pick one energy type when the feat is selected, and you stick with that selection for the rest of your career. If you want to substitute a different energy type, then you would take the feat again and select a new energy type.

[Thurbane]

But you're not actually taking the feat, you're using an X times/day ability that simulates certain metamagic feats when using magic items.

Just as you could chose to simulate either empower, enlarge or widen with each use, I see no reason you couldn't select a different iteration of the energy substitution feat.

[Tytalus]

I'm with Thurbane on this: since you don't actually gain the feat, you don't have to commit and can decide anew for each use.