TEXT: ASC – Converting Heat Errata v1.1 
  CONVERTING HEAT 
  Only units that track heat follow this step. For units that 
  do not track heat, round their damage subtotals up to the 
  nearest tenth place (e.g., 0.401 becomes 0.5). These are 
  referred to as the unit’s heat-modified damages, even 
  though the unit does not track heat. Such units then skip 
  directly to Determine Final Damage Values on the next page. 
  For units that track heat (’Mechs, aerospace fighters, Small 
  Craft, DropShips, JumpShips, satellite support vehicles, 
  space stations and WarShips), the unit’s damage values may 
  be adjusted based on the heat their weapons and 
  equipment generate in a BattleTech turn versus how much 
  of that waste heat they can dissipate. Units that possess 
  more firepower than their heat sinks can handle will find 
  their maximum potential damage reduced as a result, but 
  may also receive an Overheat Value that can be used to 
  deliver more punch as needed. 
   
  Heat Output 
  To begin, find the unit’s maximum heat output. This is the 
  heat generated by firing all weapons, as well as the special-
  case heat rules described further below. 
  ’Mech units must also add the maximum heat generation 
  possible for their most heat-intensive movement mode. This 
  added movement heat is +2 if the unit is a BattleMech that 
  lacks jump jets, or +1 per 2 inches of jumping Move if the 
  unit is a BattleMech or IndustrialMech that has jump jets (to 
  a minimum of +3 heat for such jumping units). None of the 
  other heat-tracking units covered by these rules (including 
  non-jumping IndustrialMechs) add heat for their movement 
  actions. 
  The following additional special-case rules apply to heat 
  output calculations. 
  Anti-Missile Systems: Add 1 point to the unit’s heat 
  output for every Anti-Missile System, 5 points for every Clan-
  made Laser Anti-Missile System, and 7 points for every Inner 
  Sphere Laser Anti-Missile System the unit possesses. 
  Rear-Firing Weapons: Do not include heat for weapons 
  that face into the unit’s rear unless the unit possesses no 
  front-firing weapons at all, or is a unit type capable of 
  delivering attacks into multiple firing arcs (such as a 
  DropShip, space station, or WarShip). If the unit’s front-firing 
  weapons deliver less damage than its rear-firing weapons, 
  count the heat for its rear-firing weapons instead of the heat 
  for its front-firing weapons. 
  Rocket Launchers and One-Shot (OS) Missiles: Do not 
  include the heat generated by rocket launcher weapons or 
  one-shot missile launchers of any type. 
  Stealth Systems: If the unit features stealth armor, the 
  Null-Signature System, or the Void-Signature System, add 10 
  points to its heat output. If the unit features the Chameleon 
  Light Polarization Shield, add 6 points to its heat output. 
  XXL Engine: A BattleMech or IndustrialMech unit with an 
  XXL engine ignores the regular movement heat calculations. 
  Instead, it has a movement heat of 6 if it does not mount 
  jump jets, or 2 per 2 inches of jumping Move if it does (to a 
  minimum of +6 heat for such jumping units). 
   
  Improved Jump Jets: A unit with improved jump jets 
  reduces its jumping movement heat by half, rounding up (to 
  a minimum of +3 heat for jumping). The movement heat for 
  a BattleMech with both improved jump jets and an XXL 
  engine is +1 per 2 inches of jumping Move, to a minimum of 
  +3 heat. 
   
  Heat Dissipation 
  Next, determine the unit’s heat dissipation rate by adding 
  up all of the heat modifiers shown in the Heat Dissipation 
  Table. The heat modifiers for heat sinks and coolant pods are 
  applied for each sink or pod the unit mounts, while the heat 
  modifiers for other equipment like the partial wing, radical 
  heat sink system, and RISC emergency coolant system apply 
  only once. For example, a unit with 10 double heat sinks and 
  a coolant pod would have a heat dissipation rate of –21 ([10 
  double heat sinks x –2] –1 [coolant pod] = –21). 
  If the unit’s heat dissipation rate is equal to or greater 
  than its total heat output – 4, simply round each damage 
  subtotal up to the nearest tenth place (e.g., 0.901 becomes 
  1). The result is each bracket’s heat-modified damage. 
  Proceed to Determine Final Damage Values on the next page. 
   
  Heat Dissipation Table 
   
  Equipment 
  Heat Modifier 
  Heat Sink, Standard or Compact 
  –1* 
  Heat Sink, Double or Laser 
  –2* 
  Coolant Pod 
  –1** 
  Partial Wing 
  –3 
  Radical Heat Sink System (RHS) 
  –1 
  RISC Emergency Coolant System (ECS) 
  –1 
   
  *Multiply this by the number of heat sinks the unit has 
  **Multiply this by the number of coolant pods the unit has 
   
  Heat-Modified Damage and Overheat 
  If the unit’s heat dissipation rate is less than its total heat 
  output – 4, the overall damage the unit can reliably deliver 
  may be reduced. 
  First, take the unit’s Short range damage subtotal. Round 
  it up to the nearest whole number. 
  Second, take that same damage subtotal and, instead of 
  rounding it, run the heat-modified damage formula on it:  
   
  Heat-Modified Damage Formula 
   
  Heat-modified damage = (Damage subtotal × total heat 
  dissipation) ÷ (maximum heat output – 4) 
   
  The result is rounded up to the nearest tenth place, then 
  rounded up again to the nearest whole number. 
  Lastly, subtract the value derived in the second step from 
  the value in the first. If the result is 1 or more, then the unit’s 
  actual Short Range damage value drops by that amount. 
  Once this is done, repeat the above process with the 
  unit’s Medium-range damage to find the unit’s final 
  Medium-range damage. 
  
  ASC – Converting Heat Errata v1.1 
  If the unit is a ’Mech or aerospace fighter, the amount the 
  unit’s Medium-range damage was dropped by becomes the 
  unit’s Overheat (OV) value (if the ’Mech or aerospace fighter 
  cannot deliver damage at Medium range, use its Short-
  range values instead). If this difference is more than 4 points, 
  the unit receives an Overheat Value of 4. 
  For ’Mechs and aerospace fighters, then move to Heat-
  Modified Damage—Long directly below. Otherwise, calculate 
  the heat-modified Long-range value as normal. 
  For units that possess the ability to fire multiple weapon 
  attacks in the same arc (e.g. WarShips and DropShips with 
  standard weapons, capital or sub-capital weapons, and 
  capital missiles), the heat-modified damage must be 
  computed separately by weapon class. 
   
  Heat-Modified Damage—Long 
  If the unit is a ’Mech or aerospace fighter and can deliver 
  damage at Long range (or better), the unit may receive the 
  OVL (Overheat Long) special ability. 
  To determine if this is the case, first calculate the unit’s 
  Long-range damage subtotal and round it up to the nearest 
  whole number. 
  Second, calculate the unit’s Long-range heat output. This 
  is done as normal, except that the heat from any weapon 
  with no Long-range damage value is not included. 
  Third, calculate the unit’s heat-modified Long-range 
  damage, using the normal formula, but with the above heat 
  output value. Round the result up to the nearest tenth, then 
  round up again to the nearest whole number. 
  Compare the two Long-range damage values. If the heat-
  modified Long-range damage is lower than the rounded 
  Long-range damage subtotal by at least 1 point, the unit 
  receives the OVL special ability (see p. 116). 
  Note: the above calculation is used solely to check if the 
  unit qualifies for the OVL special ability. If it does qualify, the 
  unit’s actual Long-range damage is calculated using the 
  exact same procedure and unit heat output as for the Short- 
  and Medium-range brackets (including heat generated by 
  weapons that cannot reach Long range). 
  If the unit does not qualify for OVL, then simply take its 
  unmodified Long-range damage subtotal, round it up to the 
  nearest tenth, and proceed to Determine Final Damage 
  Values. 
   
  If you have a ’Mech with a long-range damage subtotal of 
  4.5, producing 50 heat at Long range, and with a heat 
  dissipation value of 40, this is how you would check to see if it 
  had OVL and then determine its long-range damage value. 
  Step 1 involves rounding the unit’s Long-range damage 
  subtotal up to the nearest whole number. 4.5 rounds up to 5. 
  Step 2 requires you to total up all sources of heat (walking, 
  stealth armor, etc.) except for weapons that don’t have a Long 
  range damage value. For our ’Mech, this is 50 weapon heat, 
  plus 2 more for running (52 heat total). 
  Step 3 requires us to calculate the unit’s heat-modified Long 
  range damage value. (4.5 x 40) / (50+2-4) = 3.75. Rounded up 
  to the nearest tenth gives us 3.8, and that rounded up to the 
  nearest whole number gives a result of 4. 
  We then compare our two values. The heat-modified value is 
  at least 1 lower than the non-modified value. As such, the unit 
  gains the OVL special ability. 
  As for its actual Long range damage, this is calculated by in 
  the same way you calculated the ’Mech’s short and medium 
  range damage values. If the ’Mech makes a total of 53 heat 
  from all sources, then its actual Long-range damage value 
  would be (4.5 x 40 / 53+2-4) = 3.52, rounded up to 4. 
  The ’Mech has a Long-range damage value of 4, and the OVL 
  special ability. 
   
  DETERMINE FINAL DAMAGE VALUES 
  For standard and sub-capital weapons (including sub-
  capital missiles), round the unit’s heat-modified damage up 
  to the next whole number to find the unit’s final damage 
  values at each range bracket. If you already rounded your 
  damage up to the nearest whole number during the Heat-
  Modified Damage and Overheat step, do not do it again. 
  Capital Weapons: Capital weapons and capital missiles 
  are each added together and recorded separately by group 
  (one for capital non-missile weapons, and another for capital 
  missiles). Round the heat-modified sums for each of these 
  weapon classes up to the next whole number. 
  Minimal Damage: As noted under the general 
  conversion rules for weapons (see p. 99), any weapon 
  bracket that delivers more than 0 points of damage, but less 
  than 0.5 damage (before rounding), receives a Minimal 
  Damage value (0*) at that range bracket. 
  Special Ability Damage: For these values (such as AC, 
  FLK, IF, LRM and SRM damage), round the sum of these 
  abilities’ heat-modified damage values normally (not up to 
  the nearest whole number) for each range bracket. 
   
  
SOURCE: textdata/thevault/BattleTech [multi]/Core Rulebooks/errata/Alpha-Strike-Companion-Converting-Heat-Errata-2018-06-06-v1.1.pdf