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It's Getting Hot In Here


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#1 TheRAbbi

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Posted 24 November 2013 - 12:51 PM

Total newblet mechwarriors of the Inner Sphere, we've got to have a little chat about HEAT.

As was pointed out in another thread about weapons, HEAT is bad and you need to know all about it.

First, the basics.

Heat in a battlemech is generated in a few ways. Your mech's fusion engine produces heat in the process of generating the electrical power needed to operate all of the mech's systems. That's an almost negligible amount. The power plant ALSO produces heat when its power is used to move the various myomer actuators that make your battlemech move. And more importantly, most weapon systems on your mech create heat when they're fired.

SYSTEMS: The overall load for operating your mech's sensors, life support, and so on, is very low. This doesn't really warrant any further discussion, as any healthy battlemech will deal with that heat VERY easily.

MOVEMENT: Depending on how you're moving your mech, a certain amount of heat will be generated above and beyond the above SYSTEMS heat. At a walk (up to about 60% of your maximum movement speed, which includes forward and backward movement) you'll generate a small, manageable amount of heat. At a run (beyond 60% or so of maximum forward movement speed), that amount increases up to double the walking rate. Movement by Jump Jets also creates a significant amount of heat. Once a healthy battlemech comes to rest, this heat should dissipate fairly quickly.

WEAPONS: Each weapon generates considerable heat. With the exception of machine guns, ALL weapons generate SOME heat when firing. This heat will begin to dissipate almost immediately after firing. Some weapons' heat is incurred immediately (ballistic weapons, PPCs), and others throughout the firing cycle (energy weapons other than PPCs). In the case of a large laser, for instance, heat will begin to generate as the weapon is first fired, and will continue to build as the beam continues firing.

So, what to do about all that heat?

HEAT SINKS! Every battlemech contains heat sinks. A mech's engine contains between 4 and 10 heat sinks, depending on its size, and engines beyond the 275 rating may have additional heat sinks added to them. Heat sinks do for a mech's engine what a radiator does for an automobile's engine--they remove heat from the engine and exchange it with the ambient environment, all in an attempt to keep the engine's temperature within an acceptable range for optimal operation.

There are two types of heat sinks: single and double. Any battlemech may only have heat sinks of one type or the other at any time, and never a combination of both.

SINGLE HEAT SINKS: These are the millenium-old standard, mechwarriors. A single heat sink dissipates ONE point of heat over a certain period of time. Each SHS weighs one ton, and those outside of a mech's engine occupy one critical slot.

DOUBLE HEAT SINKS: These are a newer technology. They remove significantly more heat from a battlemech over the same time as a SHS, weigh the same as SHS, but occupy three times the space when installed outside the engine. DHS inside the engine remove 2 points of heat over that same certain period of time, and outside the engine they remove 1.4.

So, the consideration when outfitting your battlemech for selecting heat sinks:

If you produce less heat, but need the critical space, then use single heat sinks.
If you produce more heat and have less need of critical space, use doubles.

You'll notice that, since they take up three critical slots each, DHS cannot fit in the mech's head, center torso, or legs. Single heat sinks can fit in any of the mech's eight components (head, CT, side torsos, arms, legs). On maps that have water (all except Tourmaline Desert and Terra Therma/Mordor), SHS provide another distinct advantage. When a mech's legs are in water, the cooling efficiency of heat sinks IN THOSE LEGS ONLY increases to as much as twice normal. Thus, a SHS in the leg may cool at the same rate as a DHS in the engine, and roughly 140% that of a DHS OUTSIDE the engine, if the leg is submerged. Some maps, like River City, Crimson Strait, and Forest Colony, have a LOT of water on them. The water on Caustic Valley, on the other hand, is scarce and not in high-traffic parts of the map.

In general, light mechs have more critical space than they can use to mount weapons systems, and so DHS are a no-brainer. Assault and Heavy mechs have a lot more free weight to play with, and thus use heavier (more critical space) weapons. SHS might be a better option for those.


There is an interesting problem with weapon heat. We call it "ghost heat". When a mech mounts a number of the same weapon (6 ML, for instance), and fires them together or in rapid succession, the heat that builds up is greater than the sum of the heat for those weapons. There has yet to be a reasonable physical explanation for this, but it was done instead to balance game play a bit. The idea is that it would encourage mechwarriors to diversify their mechs' load outs. There was a time when it was not uncommon to see a JM6-DD carrying 4-6 AC/2s. But the AC/2, due to its high rate of fire, builds up a lot of heat pretty quickly (though a single shot from one builds little heat). Adding the "ghost heat" to an array of multiple AC/2s, even when chain-fired, makes it difficult to sustain a volume of fire on a target for long, and it is now often a better idea to carry only one or two of them. A favorite unconventional build for the JM6-DD was to have 2 AC/2s on one arm, and an AC/10 on the other. This kept heat manageable, gave me a better variety of weapon systems to engage a variety of targets, and resulted in some of the best match scores I've had. But it also significantly limits the ability of mechwarriors to field integrated teams of highly specialized battlemechs (one sniper, one LRM boat, one SRM boat, one medium laser boat, for instance). I'll leave it up to you to decide for yourself if it's a good or bad thing.


Ambient temperature is important to proper heat dissipation. On hotter maps (Caustic, Mordor, Tourmaline), your mech's temperature will be higher at all times, regardless of your activities (movement, firing). On cooler maps (Alpine, Frozen City), it is not unusual for your mech's resting temperature to sit at 0%. I've got a few builds that RUN at 0-1% of max temperature on those maps. It takes longer to dissipate the same amount of heat on a hot map than on a cold one.

Testing Grounds is your friend here. Use it. Each mechwarrior will have his/her own opinion as to the ideal heat efficiency number in mechlab or Smurfy. You'll need to figure out for yourself what's most comfortable for you. So, take your mech out to Caustic or Mordor. Go stand in the caldera and fire off alpha strikes until you overheat. How many did you fire? 2? 3? Go cool off, then come back and fire off your weapon groups in sequence. How long can you sustain fire before you have to lay off the trigger? How long does it take you to cool down enough to fire your primary weapon system again? YOU NEED TO KNOW THIS! Before your lance mates are counting on you to pull your weight in a drop, you already need to understand the limitations of your build. It may be that you need to drop a ton of AC/10 ammo from your Cataphract for an additional heat sink, in order to be able to fire off two alphas without overheating. You won't know until you find out, and you'll get others killed if you wait until a live drop to find out.

(FYI: About 1/3 of my playing time is spent in Testing Grounds. It's boring, because your targets don't fire back or move around. Also, bonuses from piloting skills and such do not apply in TG, so it's only so useful. On the other hand, if you've unlocked the heat-related efficiencies on your mech, then it'll perform even better in combat than it does in TG. Keep that in mind.)


Take note of pop-tarts. This is one of the most efficient practices in the game right now. They position themselves behind cover. Then they hit the jump jets. While aloft, they're out from behind cover, of course. While rising, they select a target. Once they come off the jets, they fire their heavy primary weapons on their selected target. And when they hit the ground, they're behind cover again. A good team of 2-3 snipers will take turns from different positions, and can sustain a significant volume of fire on an enemy position almost indefinitely. While one is aloft, the other is refining its position and cooling off. While it may not be the foremost consideration in the pop-tart practice, heat management is one of the big advantages of it, especially in well-coordinated teams. I've seen Jenners do it, and there's a fairly common Spider build with an ERPPC and JJs that can be pretty deadly (given that mech's inherent speed and difficulty to hit).


So, what happens if you build too much heat?

OVERHEAT, silly. What happens if you overheat your car? Well, maybe you get away with it for now. Maybe, on the other hand, you warp a cylinder head and cost a TON of money fixing your ride. Depends. Do you feel lucky?

So, your battlemech's internals are made of stuff. Stuff can't stay solid forever, and if you get it hot enough inside your mech, it won't. Remember that the stuff inside your mech is supporting part of its weight of 20-100 tons. Even a LITTLE bit of pliability can cause all sorts of problems.

I'm reminded now of a story I read YEARS ago. A certain F1 racing team developed a transmission case for their car out of carbon fiber. Why? Well, the standard was magnesium. The transmission case mounts the whole rear suspension, and a rear spoiler that could produce as much as 6,000 pounds of down force. The transmission oil tended to run at over 250 degrees F, and could potentially exceed 275 under the right conditions. Magnesium starts to get a little soft at those temperatures. The clearances and such inside that gearbox are often measured in ten-thousandths of an inch (.0001-.0009 inches), and so virtually ANY change in geometry could cause parts moving at 12,000 rpm or more to violently and catastrophically fail. That's on 3 tons of force. Your mech may put 7-33 times that much force on its internal structure just standing there, and a lot more on landing from a jump. Soft metal is BAD.

So, if your engine's temperature exceeds its maximum, it automatically shuts down. You CAN override this. I do not recommend it. The mech's heat sinks continue to work during this time, of course, and once the heat has fallen below the threshold again, the mech will automatically start back up. During that time, though, your enemies have NOT necessarily stopped shooting at you. Also, this may (and often does) cause damage to the internal structure of your mech's center torso. That means that much less damage you can take before being destroyed. You're new, so yeah, you're going to get hit in the CT a lot until you learn how not to. And overheating means a chance that any ammo you're carrying MAY explode. That includes NARC beacon and AMS ammo, but not Gauss ammo. If your ammo explodes, it does its full potential damage to the component it's mounted to. If it DESTROYS that component, then remaining damage transfers to the next more inward component (unless it is in a CASE-equipped component). So, yeah, it's kinda important to manage your heat.

Overriding heat? Cool story. Someone I know built a "death star". This is a mech with more ERPPCs than you have fingers on one hand. When fired all at once, the instant heat was more than the mech could withstand, and it would shut down. This friend tried firing it once immediately after engaging the shutdown override. The shot fired (6 or 7 ERPPCs at once... glorious destructive force!), and the not-shut-down doomsday device of a battlemech exploded BEFORE THE SHOT HIT ITS TARGET. It's kinda legendary. I'll let you figure out how to build that for yourself. Call it a 6th grade science project. Show it off. Maybe take it out once in a while with the PUGs. Good for a few giggles.

So. Stay cool, mechwarriors!

#2 Arnold J Rimmer

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Posted 24 November 2013 - 01:23 PM

With regards to map temperatures, the hot maps (Terra Therma, Caustic Valley, Tourmaline Desert) reduce both heat capacity and dissipation by 30%. So, you can fire fewer times before overheat and shuck the excess more slowly besides. Cold maps (Frozen City, Forest Colony Snow, Alpine Peaks) increase both by 30%, predictably enough. Neutral maps (River City, Forest Colony, Crimson Strait) use the capacity and dissipation shown in your Mechlab.

#3 TheRAbbi

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Posted 24 November 2013 - 04:50 PM

Thank you for clarifying that! It's good to know more precisely what we're up against!

#4 Arnold J Rimmer

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Posted 24 November 2013 - 05:19 PM

DISCLAIMER: I think it's 30%. There was a topic about this very subject written by.... scJazz (?) a while back that I've failed to find to quote correctly. Reasonably sure it's right, though.

#5 Koniving

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Posted 24 November 2013 - 05:30 PM

Jazz will interject but I believe I heard it was -20% threshold and -20% dissipation for all 3 hot maps (Caustic, Tourmaline, and Terra Therma). Forest Colony, both River Cities, Crimson Strait, and Canyon are 0%. Alpine and Forest colony snow was something like +10% threshold and dissipation, and Frozen City is +20% threshold and dissipation. These generally check out. Just in case, wait for Jazz.

#6 TheRAbbi

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Posted 24 November 2013 - 05:44 PM

I was just playing around earlier on Caustic Valley. TDR-5SS with 7 ML and 27 SHS. No, really. QUIT LAUGHING!

So, standing still outside the caldera I had heat at 5%. Walking (roughly 1/2 throttle) outside the caldera, 6%. Full speed outside, 8%. Crossed the line into the caldera. Heat was about double. Same mech, Frozen City. 0% heat at a standstill. Less than 2% at a gallop.

I think I'll do some more testing.

ALSO, for the NEWBS: weapons are irrelevant to this discussion UNTIL THEY ARE FIRED. Simply having them equipped has NO EFFECT AT ALL on heat. Even charging the Gauss Rifle doesn't have an effect on heat (though firing it generates VERY little heat anyway).

#7 Arnold J Rimmer

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Posted 24 November 2013 - 06:28 PM

I seem to remember back in Closed Beta that they changed Caustic so that the closer you got to the caldera your heat was higher. Or perhaps just inside. Either way, fighting on the rim (is silly, don't silhouette yourself) is a lot cooler than just inside it.

#8 Tabrias07

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Posted 24 November 2013 - 08:10 PM

The only mech loadouts that are better with SHS than DHS are dual gauss and other 0 heat configs, because they don't need sinks at all.

Every other mech loadout in the game is better with DHS.

Standing inside the caldera causes a load of heat.

Running causes you to lose 3 heatsinks worth of efficiency. Your % heat will depend on map temp and # of heatsinks.

Every mech has a base heat capacity of 30, and each heatsink adds to that amount equal to its cooling rate over ten seconds. In engine DHS give 2.0 (up to 10, for 20 Capacity and 2.0 Heat Dissipated per Second), further DHS add 1.4, SHS add 1.0. This means 10 DHS are as heat efficient as 20SHS for half the space and equal weight.

Pilot efficiencies also affect these amounts.

But, of course, all these values and more, including time-to-overheat and DPS, can be calculated automatically at http://mwo.smurfy-net.de/mechlab (click weaponlab)

Also, going more to more than 110% heat capacity causes you to take CT damage until you cool down, the damage scales with mech health, I forget the formula for it, I can look it up in the patch notes if anyone wants.

Overriding shutdown causes 20 damage every second or so to random locations in the mech, if (when) it hits your Cockpit, your mech will die. If it sets off any ammo, you will probably die. (1 ton of MG ammo does 80 damage) (again, listed on smurfy)

You can stop the override damage by shutting down manually, I do not believe the CT damage from overheating can be stopped. Shutting down also causes people to lose missile locks (unless you're BAP'd)

Edited by Tabrias07, 24 November 2013 - 08:20 PM.


#9 Wrenchfarm

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Posted 24 November 2013 - 08:46 PM

Thanks for saving me the time Tabrias.

There is almost NEVER a case for SHS outside of mechs using nothing but Gauss cannons, or a weapon load so ridiculously small (a single MLAS) for it not to matter.

Even in a large assault mech with plenty of extra tonnage and crits, you will likely never find a single case where SHS makes sense on an even remotely viable mech. In fact, lets try and find a way to make it work -

The AWS-8Q with SHS - an 80 ton assault mech based on light compact energy weapons. Loaded with 7 MLAS (lightest and smallest respectable weapon), we can fit in a whooping 36 SHS with all that free tonnage and crits! This gives us a respectable 51% heat efficiency (using the biggest engine for more crit spots and shaving armour from the legs to fit in an extra 2)

The same build with DHS - Able to fit 22 DHS in the available crit space, this mech has 53% heat efficiency. Oh, it also has AMS, BAP, full armour, and a spare 9.5 TONS.

If even a big empty assault mech can't boat enough SHS to make a case for them, I think it's safe to say they're useless.

#10 Tolkien

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Posted 25 November 2013 - 02:56 AM

Others have already said it but I want to repeat it just to be clear:

Single heatsinks are almost universally inferior to double heatsinks. If you think you have found a build where SHS are better, head over to the smurphy mechlab and test it.

The only cases where you don't get better effectiveness from doubles that I have seen:
1) Your mech generates next to zero heat... e.g. gauss jager. You will only have engine sinks on this mech but you should eventually get double heatsinks anyway so you can test out some other fun builds like 2x AC5 + 2xPPC, or 2x AC20.

2) You are a locust with single heatsinks in your feet standing in the water on forest colony. Those 4 SHS represent half your payload gone, so don't panic, just stand still and wait for death.

#11 TheRAbbi

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Posted 25 November 2013 - 04:40 PM

Thanks, folks. I'm going to agree that there are FEW situations in which single heat sinks are the right choice. But there ARE some. Remembering, especially, that doubles cost CB 1.5 million to install, and that the economy of the Inner Sphere isn't what it used to be, it's worth keeping in mind for new players weighing the pros and cons. That's 11-12 wins to buy DHS for a single mech once one is out of the cadet bonus stage.

Consider the following:
Posted Image

What I did here was take two Locusts on the same course around a few maps in Testing Grounds. The first, a LCT-3S, was outfitted with single heat sinks. The other, a LCT-3M, with double heat sinks. Both mechs used a 190 XL engine, which contains 7 internal heat sinks of the mech's type (SHS or DHS, respectively). In the former case, three SHS were fitted in the mech's legs. In the latter case, three DHS were fitted in the side torsos. Both mechs were run with a single Large Pulse Laser, and were identical except for the obvious difference (hard points) and the heat sink type. That is, each outfitted a 190XL, 1 LPL, 10 HS, 108 points FF Armor, EndoSteel IS, and all the normal bits belonging to a LCT chassis. The SOLE significant difference between the two was the heat sink type equipped--I even went so far as to make sure they both carried the same paint scheme, just because I KNOW someone will bring it up.

Under each mech above, you'll see five columns. S = Standing (still, at rest), W = Walking (1/2 throttle, or roughly 76 kph), R = Running (full throttle, ~153 kph), S/F = Standing/Firing (fired a single shot from the LPL while standing still with heat leveled-out at the number indicated in the S column, this is the maximum indicated heat % observed from the single shot). TIME is the amount of time it took, starting from a dead stop with leveled-out heat, firing constantly and holding a constant run, to overheat the mech. Care was taken in the TIME runs to maintain an uninterrupted full sprint on relatively level terrain--no stops or drops to drag down the mech's speed, and therefore call the constant heat of running into question. The trigger was held constantly (I may have taken a month off my LMB in that last run) from start-to-finish on the TIME runs, so that the weapon fired in a constant cycle without interruption.

Three different sets of observations were made on Caustic Valley. First was the general area of CV, second was inside the caldera, and third was in the lake water. Three more sets were made on Crimson Strait. First was dry land, then leg-deep water, and finally waist-deep water. And finally, a single set of observations was made on Alpine Peaks.

The overheat observations were made on dry land in Crimson Strait, and in the general (not caldera and not water) area of Caustic Valley.

In the three water-borne observations, the SHS-equipped 3S outperformed the 3M for movement heat dissipation. Interestingly, the 3S did not outperform the 3M when firing in water, except in the waist-deep portion of Crimson Strait. I repeated that observation a few times to be sure, and it's no fluke. It also did not outperform the 3M in the CV lake for firing, though it DID outperform the 3M for movement heat there. This demonstrates pretty well that even DOUBLING those four heat sinks was not enough to overcome the distinct advantage of the 3M's seven (7) engine-mounted DHS.

You'll notice that the 3M experienced some enhanced cooling in the deep water of Crimson Strait. It has been mentioned elsewhere, and I now believe, that ANY heat sink in ANY part of a mech that is submerged, in whole or in part, will experience increased cooling efficiency while submerged. From the third-person view, it appeared that 1/4 or less of the three torso segments was submerged in the deep water. That was observed with the crosshairs set level to the horizon beyond the playable boundaries of the map, which I assume to be level attitude for the mech.

Here's a VERY interesting observation about the positive value of DHS over SHS: While DHS do 1.4-2.0 times as efficient a job of keeping the mech cool, it doesn't mean that you ONLY get that much longer. Heat builds and dissipates over time, of course. In the overheat run on Caustic Valley, the 3M lasted almost 2.3 times as long without overheating. The total points-per-round cooling capacity of the 3M's heat sinks was 1.82:1 to the 3S's SHS. The relatively long cool down time of the LPL gave the DHS more time to do their work. The 3M took nearly 2.7 times longer to overheat on Crimson Strait, further exaggerating the benefit of DHS. And on Alpine Peaks, it took over 6.4 times as long to overheat the 3M. No light mech is going to survive enemy fire for over 4 minutes if it runs around non-stop firing its primary weapon, so the measure means that a light could virtually fire non-stop with impunity at this cooling efficiency.


SO, what's it all mean? Well, if you like to wear the wading boots, and you don't create too much heat from firing your weapons, then: A.) You're playing the wrong game, and B.) You're likely to get more mileage out of SHS mounted in the legs. Otherwise, shoe-horning as many DHS as possible into your mech is almost certainly the way to go.

In other words, what the folks above me said.





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