D20 Mechanic: Healing Surges
Here we discuss healing surges as used in d20.
You have a number of healing surges as specified by the class in which you have the most levels; if you have equal levels in multiple classes, you use the highest number of healing surges from among those classes. If leveling would cause you to have more healing surges than your maximum, you lose only enough healing surges to bring you to your new maximum.
Many powerful healing effects consume your healing surges. Whenever a healing effect would consume a healing surge, it will either specify how many hit points it restores (such as a medic's treat injury ability), or will heal you for your healing surge value (see below).
Some classes, such as the defender, can gain access to abilities that allow them to spend their healing surges on abilities. If you spend a surge in such a way, you do not gain hit points from its expenditure.
Healing Surge Value
Some effects may call upon your healing surge value, which is equal to 25% of your maximum hit points, rounded down.
If an effect simply states that you may spend a healing surge without specifying how much healing it provides, the expended healing surge heals you for an amount of damage equal to your healing surge value.
Once per encounter, you can expend a single healing surge on your own. Doing so is a move action, and heals you for damage equal to your healing surge value.
This ability "recharges" similarly to martial maneuvers; so long as you're out of combat for roughly a minute or so, you can catch your breath and wind down, regaining the the ability to use a second wind in the next encounter.
Outside of combat, you can spend as many healing surges as you like to regain hit points, provided you have at least 1 hit point remaining. Doing so requires at least 10 minutes of downtime, and each healing surge you spend in this manner requires one use of a healing kit (or repair kit, if you are a construct or similar creature that cannot heal naturally).