Try this as an experiment:
1. go to the mechlab (any mech)
2. strip all equipment. 'strip' is found in the "mech stats" tab.
3. add an engine (any engine STD or XL, preferably something middle-rating halfway down the list)
4. add an energy weapon (any will do, but preferably something that generates a lot of heat, say, a PPC)
(NOTE: don't add any heat sinks at all)
...so at this point you've got a mech with an engine and a weapon...
5. take note of your heat rating ("HEAT MGMT"). it's found in the "mech stats" tab.
6. add more weapons till it's more or less 1/2. any weapons will do.
(NOTE: heat ratings go from 0/2 to 2/2. 1/2 is a bare minimum, 1.5/2 is good, anything higher is great)
7. switch to double heat sinks
8. again, take note of your heat rating ("HEAT MGMT").
you'll notice that your heat rating jumped from around 1.0 to around 1.4; a 40% increase as stated in the "double heat sinks" tooltip.
all engines have magic hidden heat sinks built into them. as you lower your engine rating (IE select lighter engines), you're forced to make up for the reduced magic heat sinks by adding actual physical heat sinks into the mech equipment slots.
(anyone who's ever tried to custom build a locust knows the hell i'm talking about!
if you don't know, then try going up and down the engine rating scale... save 1.5 tons, lose 20kph and 1 ton&slot for another damn heat sink)
the point of the above steps is to see
statistically that switching from single to double also switches the magic hidden engine heat sinks, thus giving you the +40% bonus,
even if you havent added any heat sinks into any slots manually.
for low-tonnage laser boat builds, this is immensely helpful. with this you can go ferro-fibrous and endo-steel (eating up 28 slots and giving you a few extra precious tons), throw your weapons on, and still try to squeeze some heat sinks into the last remaining slots/tons.
most of your heat management comes from the magic engine heat sinks.
this is where heat balancing comes into play, adding or changing weapons in accordance with their HPS (heat-per-second) rating, and moving ammo around to free up slots for the odd heat sink here or there.
you might have the tonnage to slap on 3 large lasers, but if your heat rating isnt close to 1.5, you'll spend more time shut down than fighting.
you'll need to calculate HPS manually as follows: in the weapon tooltip, simply divide the "HEAT" by the "COOLDOWN". this is how much heat, on average, is generated by that weapon per second. i dont know how the values translate to heat % in the field, but it's a great way to compare weapons with each other and it is essential for building mechs that won't overheat.
this calculation is the same as calculating damage-per-second DPS; "DAMAGE" divided by "COOLDOWN". FIREPOWER shown in the mech stats tab is just the sum total of all your weapons' damage, as if all fired at once (aka "alpha strike").
whether calculating HPS or DPS, you'll need to figure out if you're going to be doing hit-n-run type stuff (focus FIREPOWER) or continuous damage (focus DPS & HPS).
range is also a factor.
Medium Lasers and Small Pulse Lasers are some same slottage and tonnage (1 and 1), but the SPLs give you higher DPS and lower HPS, at the cost of range. on the other hand, MLs give you better alpha strike firepower. which fits your intended playstyle?
another way to go is if you're using low-heat weapons, you can still go double, switch to ferro-fibrous and endo-steel, then use all the remaining slots for weapons and ammo without having to worry about using any slots at all for big fat double heat sinks.
sorry for rambling, my point here is that
double heat sinks improve your heat rating even without any manually-added heat sinks, enabling you to have better heat control without losing slots or putting ammo in your legs (LOL!)
before buying a mech, make sure you have enough to cover the cost of a different engine and any ferro/double/endo/artemis changes you intend to make.
in fact, i always make a full finished custom-built setup before i buy anything, and i actually (roughly) calculate how much i'll need so i dont go broke when i make the purchase.
hope that wall of text helped.
Edited by Generic Internetter, 27 December 2015 - 04:24 PM.