Heat Scale is a system that penalizes a mech with extra heat generation when multiple weapon systems of the same or similar types are fired within a short time frame. It is commonly referred to as "Ghost Heat" by the community due to a lack of in-game information on how the system works and UI notifications when a penalty occurs. The goal of the system is to limit the practice of taking large quantities of the same or similar weapon systems ("Boating") and firing them at the same time ("Alpha Striking").
Weapons that have similar firing profiles are likely to be used together in an alpha strike and therefore are typically linked into a penalty group. For example all types of the large laser (Regular, Pulse, Extended Range and Heavy) are linked together into a single penalty group. The penalty for firing more than the allowable limit of linked weapons will still occur even if you mix and match the several different types of that weapon. However an important aspect of this is that allowable limit from one group doesn't effect the allowable limit for another group. If you take a range of weapons from different penalty groups that are individually under their allowable limits, all of the weapons can be fired at once with no penalty. A common example is the combination of the large laser group and the medium laser group such the large pulse laser and the extended range medium laser. Both of these weapons have almost identical range and duration making them perfect candidates to be combined in this way. This is why you will see experienced players taking specific quantities of different weapons on their mechs.
Heat scale penalties are calculated based on how many weapons within a predetermined group are fired together.
Some weapons have no limit and can be fired without penalty
Some weapons are in a penalty group by themselves and can be mixed with any other weapon without a penalty
Some weapons are in a penalty group with other weapons and will generate a penalty if mixed with those weapons.
Each weapon within a group has its own number of weapons before a penalty is applied, however when mixing weapons the lowest number is used.
For example, while 2xMRM30 are allowed without penalty, only 1xMRM40 is allowed without penalty.
If a pilot mixes 1xMRM30 and 1xMRM40 a penalty will be incurred since the lower limit of 1 from MRM40s is used instead of the 2 from MRM30s.
To calculate the penalty heat from firing some combination of weapons you must know three pieces of information for each weapon over the allowed firing limit: The base heat of the weapon, the penalty rate and the penalty multiplier. The penalty calculations are done separately for each weapon past the allowable limit then added together to get the final result.
When dealing with mixed weapon groups the base heat used in the calculation will be the highest value from the weapons involved. For example PPC and Gauss type weapons are linked in heat scale with an allowed limit of 2. If a combination of Gauss and PPC would cause a penalty, the calculations will be based on the heat value of the PPC as it is the higher of the two.
The penalty rate depends on the allowed limit of the weapons involved and how many weapons over the limit were fired. Knowing those you can use the table below to determine the penalty rate for the calculation. With our previous example of Gauss and PPC we know that the allowed limit for those weapons is 2. If a third weapon of that type is fired its penalty rate will be 0.18, a fourth weapon would have a 0.30 penalty rate and so on.
The penalty multiplier is
Total Heat = Base Heat + (Base Weapon Heat x Penalty Rate X Multiplier)
Each of these are calculated separately for each weapon past the allowed limit.
For example PPCs have a base heat of 9.5, multiplier of 7 and allowed limit of 2.
Firing 2xPPC is within the allowed limit and only base heat is applied.
Firing 3xPPC is 1 over the allowed limit and penalty heat is applied. The penalty rate for a 3rd weapon is 0.18
Therefore the calculation is Base Weapon Heat x Penalty Rate X Multiplier or 9.5 x 0.18 x 7 = 11.97 heat.
Adding that penalty to the base heat of 3xPPCs (28.5) equals a total of 40.47 heat.
Firing 4xPPC is 2 over the allowed limit and penalty heat is applied. The penalty rate for the 4th weapon is 0.30
Therefore the calculation is Base Weapon Heat x Penalty Rate X Multiplier or 9.5 x 0.30 x 7 = 19.95 heat.
Adding that penalty to the base heat of 4xPPCs (38) and penalty for the 3rd PPC (11.97) equals a total of 69.92 heat.
This process is repeated for each weapon past the allowed limit.
When weapons are mixed these calculations will be done with the highest base heat of the weapons involved.
If in the above example instead of 4xPPC being fired, 3xPPC and 1xERPPC were fired the heat penalty calculation would use the base heat of the ERPPC.
Big table showing the heat scale penalties and groupings of weapons
Total Heat Penalties per Weapon Grouping
No penalty = Green Text
Penalty = Orange Text
|AC/20 Linked Group: Limit = 2, Penalty Rate = 24|
|- |AC/20 | | | | | | | | | | | |