Multiplier (I think 0.5 might work) x Base weapon heat x Number of units fired = heat penalty
Have the penalty kick in whenever you fire more than one weapon of a type at a time (with a 1 second wait in between shots), so nobody gets to play favorites with the minimums based on stock loadouts or what have you.
Yes, lower heat weapons will still be penalized for being fired in groups (two or more), but being lower heat means the penalty still wont be as drastic as something hotter.
4 AC/2s (1 heat per gun): 0.5 x 1 heat x 4 guns = 2; base heat for four simultaneous AC/2s is going to be 4 with an additional 2 heat for the penalty (6 heat per group fire)
4 PPCs with the new heat (9 heat per gun): 0.5 x 9 x 4 = 18; base heat for four simultaneous PPCs is going to be 36 with an additional 18 heat for the penalty (54 heat per group fire)
8 Medium laser (4 heat per beam): 0.5 x 4 x 8 = 16; base heat for eight simultaneous medium lasers is going to be 32 with an additional 16 heat for the penalty (48 heat per group fire)
2 AC/20s (6 heat per shot): 0.5 x 6 x 2 = 6; base heat for two simultaneous shots is going to be 12 with an additional 6 heat penalty (18 heat per group fire)
Now, that is just a sample, and there are definitely some weapons that benefit from this system far more than others, like that AC/20 (gauss also still avoids any major penalty because ghost heat is a dumb idea, but w/e), but in those cases I would suggest changing base heat or cooldowns (could also affect round length). The reason I suggest changing weapon values is because I think data not readily available to players on the front end should be relatively uniform and easy to understand if looked up (see: engine sizing, speeds, and sinks). Equipment having different heat and cooldown values is fine because it's all on display, but ghost heat (if hidden) needs to follow a single formula IMO.
TL;DR: If ghost heat is going to stay, it should be a core part of the heat system, not applied to weapons on a case by case basis.
Edited by skullman86, 26 July 2013 - 01:32 PM.