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A while back I posted a discussion asking if anyone had ideas for making a healing surge system for 3.5e. Ghostwheel delivered, and his system can be found here. It's a fine system, and it's undergone quite a bit of changes over time. My variant rule will be pretty similar. The goal of my healing surges will be to take some of the burden off clerics (and anyone holding a wand of cure light wounds), and get everyone back in the fight.
A healing surge is that kick of adrenaline in combat that can get you back in the game. A healing surge is defined as one quarter of your total maximum hit points, rounded down. If Tordek has 64hp, each of his surges is worth 16hp. If Lidda has 42hp, each of her healing surges is worth 10hp. Your number of healing surges per day is limited by your Constitution modifier, plus a number assigned based on your class. You may not use your healing surge to gain HP beyond your maximum. If you do not need all of the HP, they are wasted. HP from a surge cannot be saved until later.
Every character gets a number of healing surges per day. To calculate the number of healing surges per day you get, divide the number of sides on your HD in half. That means if you're a wizard (or anyone else with a d4 HD) you have 2+your CON modifier surges per day. Multiclass characters use the most common HD they have. If you are a Wizard/2, Rogue/3, Sorcerer/2 then you have 4 d4 HD, so you get 2+COn surges a day. However, if you are a Wizard/2, Rogue/2 and have equal number of HD, you may use the higher number.
Using a Surge
There are a few instances in which you can use a healing surge. Each of them will be described in detail below. No matter what condition allows you to use a healing surge, you don't have to use a healing surge, and you must still have surges in order to use one. That is to say, for example, if you have already used your daily allotment of healing surges you can't take a second wind.
A character can take a standard action, which does not provoke an attack of opportunity, to use their "Second Wind", allowing them to take a healing surge. This can only be done once per encounter. For example, Tordek is fighting a red dragon, and is hit by 2 claw attacks. He decides he wants to take his second wind. On his turn he may spend a standard action to gain one quarter of his hit points instantly. There are no rolls or checks for taking a second wind.
After a cure spell
If a character is the target of a cure spell, they may spend a healing surge as a free, and immediate, action to cause the healing spell heal double, up to a maximum of the target's normal surge value. This is purely optional. For example, Ember the monk was hit by a lightning bolt spell. On the cleric's turn, he decides to cast Cure light wounds (normally 1d8+5) on Ember. Ember decides to use a healing surge at this time, so she gets 2d8+10 hp, up to a maximum of 14 (her normal surge value).
Out of Combat
If you are doing something considered non-stressful, such as camping, riding a cart, or even walking or riding at a leisurely pace, you may spend a healing surge. For example, after getting through all the traps, Lidda decides to rest on her pile of gems and nurse her wounds. She may spend a single healing surge and get back a quarter of her hit points.
Camping for the night
If you have decided to camp for the night, you can take one full hour, and spend as many healing surges as you would like. If you are interrupted before the hour is complete by anything deemed stressful (a random encounter, for example) you gain no hit points, but none of the daily uses are expended, so you may try again. For example, Krusk has spent all day being arrowbait for his party, and at nightfall he decides it's time to tend to his wounds. He can spend an hour spending as many healing surges as he wants/can, assuming he doesn't enter combat or do anything else stressful.