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Heat is one of the major game mechanics in MechWarrior Online and something that sets it apart from other shooters. To be successful in the game you must have an understanding of the heat system and its various aspects. The system can be broken down into three major components; Generation, Capacity and Dissipation.

Generation is any creation of heat from one of many sources. Primarily heat will be created through the firing of weapons which have an associated heat value, when you fire that weapon that amount of heat is added to your mech. There are other less common ways to add heat to your mech such as heat transferring weapons like the Flamer or environmental effects such as lava pools.

Capacity is the amount of heat a mech can store at any one time before overheating. The capacity for any mech starts at the base value of 30 and is increased for each heat sink added to the mech.

Dissipation is the rate at which heat is removed from a mech. This rate is entirely based on the quantity and quality of heat sinks equipped on the mech.


If at any time your mech passes 100% heat capacity it will shutdown until the excess heat is dissipated. While you are shutdown due to overheating the HUD will disappear and your screen will turn red. If you exceed the heat capacity by a large amount you will also take incremental internal damage on your center torso. You can tell when you are receiving this damage due to a yellow strobe light that will flash from within your mech's cockpit. Note that this damage is applied directly to your internal structure and therefore ignores any armor.

Override Shutdown

It is possible to prevent the automatic shutdown that occurs when a mech overheats using the override toggle. By activating the toggle ('O' by default) your mech will no longer shutdown after reaching 100% heat and will continue to function. However the drawback to overriding is that your mech will take severe internal damage every second that it remains active while over 100% heat. This internal damage is randomly assigned to any section of the mech aside from the cockpit. It may be tactically beneficial to stay powered on and take the override damage rather than shutdown in a vulnerable position.

Heat Scale

Heat Scale is a system that penalizes equipping your mech with multiple of the same or similar weapons (Boating) and firing all of those weapons within a small time frame (Alpha Striking). While it is still possible to do such actions the system will add extra heat to your mech proportional to the type and amount of weapons fired. Weapons are separated out into different penalty groups, some occupy a group by themselves while others are group with others that have similar firing profiles. You are able to tell if any specific weapon type or combination of weapons will cause a penalty when fired in an Alpha Strike by checking the Load-out Error panel as seen in the example on the right.

A list of the current Heat Scale groupings and penalty rates can be found on Smurfy.

Loadout error screen showing a heat penalty warning for equipped ATMs/LRMs

Heat Sinks

Heat sinks are a type of equipment that dissipate built up heat and increase maximum heat capacity when mounted on a mech. There are two types of heat sinks; Single heat sinks which are more compact but offer weaker benefits and double heat sinks which occupy larger space but provide greater benefits. You can only equip one type of heat sinks at a time and in order for a mech to have a valid load-out in the Mech Lab it requires at least 10 heat sinks to be equipped.

Internal Vs External

Heat sinks can either be internal as part of an engine or externally in other locations on the mech. An important distinction is that internal heat sinks are only the ones that come with the engine's base wight and do not include any you place in engine heat sink slots for engines of 275 rating or higher. Any heat sinks placed in those engine slots are considered external heat sinks for their dissipation and heat capacity values. You can determine the amount of internal heat sinks within an engine by looking at it's rating; for every 25 rating an engine has, it gains an additional internal heat sink up to the maximum of 10 at 250 rating. Past 250 the engines will instead gain heat sink slots for every 25 rating, and as mentioned above heat sinks in those slots count as external heat sinks. These are shown on the Mech's stats as external/(internal) as highlighted in the image on the right.

See the page on Engines for a list of how many internal heat sinks are provided by each engine rating.

Mech stats showing standard heat sinks equipped with 1 external and 9 internal heat sinks.

Single Heat Sinks (SHS)

A basic equipment that weighs 1 ton and occupies 1 critical slot. Each SHS provides an additional 0.12 heat per second dissipation and 1.2 maximum heat capacity for the mech. These values are identical for both internal and external heat sinks as well as the different tech bases of Inner Sphere and Clan. The small size of SHS allows them to be fitted in cramped spaces and provide more dissipation per critical slot than their double heat sink counterpart. However heat dissipation per ton is typically more important to the majority of Mechs with only specific Assault Mechs able to utilize SHS in a sufficient quantity. Therefore it is standard to upgrade almost every mech with double heat sinks.

Double Heat Sinks (DHS)

An advanced piece of equipment that weighs 1 ton and occupies 3 critical slots for IS tech and 2 critical slots for Clan tech. Each DHS provides an additional 0.15 heat per second dissipation and 1.5 maximum heat capacity for the mech. These dissipation values are identical for the different IS and Clan tech bases but differ between internal and external mounting. External DHS provide the standard dissipation as listed above however internal DHS have their heat dissipation boosted to 0.2 heat per second. This means that an engine with 10 internal DHS has a total of 2.0 heat dissipation compared to SHS with 1.2 heat dissipation. This is approximately 67% more heat dissipation with no downside of increased critical slots as internal heat sinks are built into the engine and the increased critical size of DHS is not a factor.

A 300 standard engine with 2 external heat sinks placed into the engine slots.

Effects of Map Environments

Heat Dissipation Modifiers
HPG Manifold -0.15
Frozen City -0.13
Boreal Vault -0.13
Polar Highlands -0.11
Alpine Peaks -0.1
Boreal Reach -0.1
Grim Plexus -0.08
Ishiyama Caves -0.08
Grim Portico -0.07
The Mining Collective -0.02
Crimson Strait -0.01
River City 0
Steiner Colosseum 0
Emerald Taiga 0.01
Hellebore Springs 0.02
Forest Colony 0.03
Viridian Bog 0.04
Canyon Network 0.05
Mech Factory 0.08
Sulfurous Rift 0.09
Liao Jungle 0.10
Rubellite Oasis 0.11
Caustic Valley 0.12
Tourmaline Desert 0.13
Vitric Forge 0.14
Terra Therma 0.15

There may be environmental factors on the map that effect your mech's current heat and heat sink efficiency. These can range from Lava flows that will add heat to your mech or pools of water that will increase your heat sink's dissipation rate.

Map Temperature

The ambient temperature of a map will effect the dissipation rate of a mech's heat sinks. While the temperature displayed on the map loading screen is entirely cosmetic, it does give an idea of what the actual dissipation modifier will be. Each map has it's own global modifier that is in effect for the entire map area and possibly regional modifiers that effect only a small portion of a map. For example while Caustic Valley may already have an increased global modifier it is further increased in the region of the volcano's caldera. So far regional modifiers have only increased heat compared to the global modifier.


Submerging a section of your mech in water will increase the efficiency of any heat sinks that are installed in that section proportional to the amount it is submerged by. For example having two single heatsinks in your right leg and your right leg being 75% submerged in water will give those two heatsinks a 75% cooling boost. This cooling boost is highly dependent on the size, hit-boxes and technology base of the mech in question. Lighter and smaller mechs will be able to submerge a higher percentage of their sections within a body of water compared to a heavier and larger mech. Also since legs are typically the only parts to be submerged within shallower waters, Inner Sphere mechs that upgrade to double heat sinks will be unable to utilize this cooling effect as their heat sinks would no longer fit within the 2 slots of a leg.


So far the only map to have lava pools present is Terra Therma. Standing in pools of lava will slowly increase your mech's heat up to a maximum of 90% and cause incremental leg damage. Your heat will not pass that 90% capacity so there is no fear of overheating and shutting down solely due to the lava and being stuck unable to restart your mech and move out of the lava pool.

External Heat Transfer

A few mechs have a unique quirk that reduces the effects of these environmental modifiers by a percentage. So far this is limited only to the Night Gyr chassis at 100% and Battlemaster's Hero "Hellslinger" at 25%. This can be either a positive or a negative depending on the situation. While the negative effects of a hot environment will be reduced, the beneficial effects of a cold environment will also be reduced. In general this quirk makes the mech more consistent so it performs similarly no matter the environment being fought in.

Effects of Movement

Engine Throttle

Just by moving a mech it creates a small amount of heat. These penalties are the same going forwards or backwards and only consider what percentage of the top speed the mech is traveling at and not the absolute value of that speed.

  • At 66% throttle the engine generates heat up to the equivalent of 1 single heatsink.
  • At 100% throttle the engine generates heat up to the equivalent of 2 single heatsinks.

As detailed in a breakdown post.

Effects of Equipment

Jump Jets

Firing a mech's jump jets will add heat at a constant rate to your mech depending on how many jump jets are being used. On a mech with low dissipation rate this will actually cause heat to build up over the time span of jumping.


Flamers will add heat to an enemy mech for each second they are hitting their target.

Stealth Armor

Similar to jump jets, stealth armor will add heat to your mech at a constant rate. While the majority of designs will slowly increase in heat while stealth armor is active it is possible to dissipate heat if enough heat sinks are taken.


A temporary heat management tool, the coolshot consumable can be used in emergency situations to quickly dissipate a large amount of heat.