Health over Time (HoT) is a statistic that increases the rate at which a player character regenerates HP. All characters have an innate Health over Time rate, which increases (or "ticks") HP every six seconds. Each point of HoT thus increases the HP regenerated every six seconds by one point.
HoT may be increased in two ways: via class masteries and via item bonuses. The way that HoT functions and stacks differs in both cases.
HoT acquired via CMs will stack with itself and with gear. For instance, if a player purchases a CM that provides +4 HoT, and then a subsequent CM that provides +4 HoT, the player will have gained 8 HoT in total.
HoT acquired via multiple items suffers from diminishing returns. The item that provides the highest HoT will always provide HoT at its full value. A second item equipped that provides HoT will only provide 50% of its statistic value in actual HoT. And each additional item providing HoT equipped after a second one will provide only 1 HoT value, regardless of its actual HoT statistic. For instance, if a character equips 4 items that each provide 20 HoT, the character's overall HoT total will only increase by 32 (20 HoT for the first item, 10 HoT for the second, and 1 HoT for each additional piece.)
HoT is typically not considered a valuable raiding statistic at level 60. It can, however, be of use while leveling, especially during the early levels while solo (or otherwise without a traditional healer), saving the time and costs associated with using food items to heal between battles.
HoT may be increased via the following class masteries:
For classes that ensure substantial lifetaps as a consequence of some abilities (such as a necromancer's lich form which incurs a 199 dmg DoT) HoT can provide a valuable means to mitigate that damage and avoid the need for healing.