Healing Amplification

Healing Amplification increases the hit points cured by healing spells and effects. It stacks with effects that increase the power of healing spells, such as metamagic feats (e.g. Empower Healing), class enhancements (e.g. Cleric Life Magic), item enchantments (e.g. Devotion), scroll mastery enhancement, etc. Incoming healing is simply multiplied by character's total healing amplification.

Healing amplification comes from race, class, items, and miscellaneous sources. These stack, but special rules apply.

Total heal amp = racial amp * class amp * item amp * misc (* misc) (* misc) ... + Fleshmaker

Racial bonus
Most races don't have racial bonuses to healing amplification, i.e. their racial multiplier is 1.
 * Human Improved Recovery has three stacking tiers of 10% each for a maximum multiplier of 1.331.
 * Half-elves can take two tiers of Human Improved Recovery for a maximum multiplier of 1.21.
 * Warforged start at 0.5 and can take Healer's Friend enhancements three stacking tiers of 10 each (10/20/30) increasing racial multiplier to 0.80.
 * Docent of Blood is an item, but stacks differently than most items. Its 0.1 (10%) is added to Warforged racial heal amp, for a total of 0.90 (when Healer's Friend is maxed)

Class bonus
Class bonuses from different classes stack (are multiplied).
 * Monk Improved Recovery has three stacking tiers of 10% each for a maximum multiplier of 1.331.
 * Half-Elf Monk Dilettante enhancements (Half-Elf Improved Recovery) has two stacking tiers each for a maximum multiplier of 1.21. (This is a class bonus, stacks with racial, locks out monk's amplification)
 * Paladin prestige enhancement Hunter of the Dead (10% per tier of the PrE, stacking separately for a total of 33.1% at tier 3)

Item bonus
The healing amplification item enhancement comes in three levels (10/20/30 %). Items with the same level do not stack. Items with various levels of healing amplification stack. The bonuses are multiplied, for a total of 1.1 * 1.2 * 1.3 = 1.716. (71.6% total amplification)

Healing amplification 10%
 * Dragontouched Armor, Eldritch
 * Greensteel Weapon - Tier 1
 * Lesser Convalescent random loot
 * Vengeful Protector

Healing amplification 20%
 * Tira's Splendor rune arm
 * Convalescent random loot
 * Dragontouched Armor, Tempest
 * Greensteel Weapon - Tier 2
 * Levik's Bracers (From Hound of Xoriat raid)
 * Can be crafted on Tower of Despair Rings (Incredible Potential)
 * Epic Bejeweled Letter Opener
 * Wall of Wood (Level 22)

Healing amplification 30%
 * Greater Convalescent random loot
 * Greensteel Weapon - Tier 3
 * Epic Gloves of the Claw
 * Purple Dragon Gauntlets
 * Wall of Wood (Level 23)

Miscellaneous bonus

 * Paladin Passive Past Life Feat (stacks additionally 3 times, for a total of 5%, 10% or 15%)
 * Jidz-Tet'ka - +25% insight bonus for Monks in fire stance.
 * House Jorasco Healer Contract from Guild Airships (10 %)

Fleshmaker
The Fleshmaker item enchantment adding 10% has a unique mechanics and stacks in a different way. For best effect, equip the Fleshmaker item first and then add other sources of healing amplification. In most cases the net result will be slightly over 10%, and as high as ~17% if you equip all three tiers of standard healing amp after your fleshmaker item.

healed hp = base heal amount * heal amp +  base heal amount * heal amp sources equipped after fleshmaker * 0.1 (fleshmaker)

For example, when you equip heal amp 10 %, fleshmaker, and heal amp 20% and use a heal scroll:

healed hp = 110 * 1.1 * 1.2 +  110 * 1.1 * 0.1 = 145 + 12 = 157 (If fleshmaker gave only 10%, the expected value would be 156.) (If it stacked like healing amplification items, the expected value would be 110 * 1.1 * 1.2 * 1.1 = 159.)


 * Healing Amplification guide by vyvy3369, explains the unusual way Fleshmaker works