How does non-lethal damage interact with temporary HP?

Question

I need to figure out how temporary HP and non-lethal damage interact. I am an unchained Summoner who has been allowed to take the Synthesist archetype from summoner. This allows me to wear the Eidolon as armor and basically get most of its abilities as my own. This allows me to treat the Eidolon's HP as temporary HP. Now as I keep this temporary HP until its depleted or the Eidolon is unsummoned, how does non-lethal damage interact with it?

So when you are damaged it reduces your HP, and when you take non-lethal damage you count it, and when non-lethal equals you are staggered, and greater you are knocked out. I must again thank this answer for clearing this up so nicely.

So does temporary HP get counted in? Would I add both temporary HP and HP together to determine when I am staggered or knocked out from non-lethal, or do I still only consider HP? This is important because there are ways for me to replenish my temporary HP and sacrifice my HP to keep the Eidolon around.

Answer 1

Short answer: temporary HP count towards determining when a character is staggered by taking nonlethal damage.

A creature with nonlethal damage exactly equal to its current hit points gains the staggered condition.

Before adding temporary hit points into the mix, the way it works is that a fully-healed creature has their max HP and 0 nonlethal damage. As they take damage, they deduct lethal damage from their current HP and add nonlethal damage to their nonlethal damage total.

Action           | HP | Nonlethal Damage | Condition
wake up          | 10 | 0                |
take 2 dmg       |  8 | 0                |
take 2 nonlethal |  8 | 2                |
take 6 nonlethal |  8 | 8                | staggered

Temporary Hit Points:

Certain effects give a character temporary hit points. These hit points are in addition to the character’s current hit point total and any damage taken by the character is subtracted from these hit points first. Any damage in excess of a character’s temporary hit points is applied to his current hit points as normal. If the effect that grants the temporary hit points ends or is dispelled, any remaining temporary hit points go away. The damage they sustained is not transferred to the character’s current hit points.

When temporary hit points are lost, they cannot be restored as real hit points can be, even by magic.

(emphasis mine)

Temporary hit points are real hit points, and they affect when a creature is staggered.

Action              | HP | Nonlethal Damage | Condition
wake up at full hp  | 10 | 0                |
take 2 damage       |  8 | 0                |
take 2 nonlethal    |  8 | 2                |
take 6 nonlethal    |  8 | 8                | staggered
gain 2 temporary hp | 10 | 8                |
take 1 damage       |  9 | 8                |
temporary hp ends   |  8 | 8                | staggered
heal 7              | 10 | 1                |
gain 9 temporary hp | 19 | 1                |
take 5 damage       | 14 | 1                |
take 13 nonlethal   | 14 | 14               | staggered
heal 1000           | 14 | 0                |

Answer 2

Your temporary HP is considered into your Current HP when deciding how much non-lethal damage is required to knock you out.

Think of non-lethal damage as damage to your minimum health level... essentially it raises your '0' HP to be a higher level. Until your non-lethal is greater than your current HP but less than your (base) current HP+temporary HP, your question won't even come up since temp HP is (generally) lost first.

Generally, if this case does happen, your temporary HP still counts as current HP for keeping you awake when taking non-lethal damage.

Certain effects give a character temporary hit points. These hit points are in addition to the character’s current hit point total and any damage taken by the character is subtracted from these hit points first.

A strict RAW reading might deem that "These hit points are in addition to the character's current hit point total" does not mean temporary hit points are considered into current hit points, but instead they are their own pool that is not 'current hit points. However, I feel like the word 'addition' indicates that RAI is adding them for a new 'current hit point total'.