Temporary Hit Points

[Daviot44]

Do they stack? The entry on temp HP doesn't say one way or the other, and the combat chapter talks about bonuses to attacks and defenses and stats and seems to mention everything except HP as far as different types of bonuses stacking. Or is "Temporary" supposed to be considered a "type" of bonus like "deflection" is?

[Quandary]

I would say yes.
HPs, temporary or not, are not 'bonuses'.
HP DAMAGE (i.e. negative HPs) stacks, right? HPs from cumulative Hit Dice is treated as stacking, right?
So I would assume further (Temporary) HPs also stack unless explicitly directed that they don't.

[Maezer]

In 3.5 temporary hit points from different sources stacked. This was a long standing FAQ ruling. I believe the Pathfinder temp hit points SRD entry and the 3.5 entry are identical, so I would assume the ruling remains the same. But there have been threads about this on the paizo boards but I haven't seen an official posting.

WotC 3.5 FAQ wrote:

Do temporary hit points from two applications of the same effect stack? What about from different effects? If I have temporary hit points from multiple sources, how should I apply damage?

Temporary hit points from two applications of the same effect don’t stack; instead, the highest number of temporary hit points applies in place of all others. Temporary hit points from different sources stack, but you must keep track of them separately.

For example, imagine a character who gained 15 temporary hit points from an aid spell. After taking 8 points of damage, she has 7 temporary hit points left from the spell. If another aid spell were cast on the same character granting 12 temporary hit points, this total would replace the other spell’s total, meaning the character would now have 12 temporary hit points (rather than 19). If the character then cast false life on herself, she would add the full benefit of that spell to the temporary hit points from the aid spell.

This also applies to temporary hit points gained from energy drain and similar special abilities. Each successful attack counts as one application of the effect (meaning that an attack that bestows 2 or more negative levels still counts as only one application of the effect). For example, a wight gains 5 temporary hit points each time it bestows a negative level with its slam attack. If it bestows another negative level while it has 2 temporary hit points remaining from the first attack, the new temporary hit points would replace the old ones.

Temporary hit points are “first-in, first-out.” Damage should be taken off the oldest temporary-hit-point-granting effect first; when that effect is exhausted, apply damage to the next oldest effect. For this reason, you must track each supply of temporary hit points separately.

[Rezdave]

Note that, generally, "temporary" hit points are "top points" and thus the first lost in combat, but a few spells or effects give them as "bottom points" and they are effectively lost last, meaning if you haven't healed any damage to them by the time the effect ends you are disabled or dead. Effectively, they are a temporary "reserve tank" that suddenly will leak/evaporate after a time.

Bonus HP from CON effects are exactly this type of "bottom points". If you receive bear's endurance and gain several hp, then are dropped to 1hp by the time the spell ends, you will take at least 2hp of "loss" (if 1st level) and be in negative HP if not dead, depending upon your level.

Spells which give "bottom points" are very specific about that fact in the text. Otherwise, assume that temporary HP are the first lost when any damage is taken.

HTH,

Rez