Originally posted by Metalhead123: ...This isn't recent. It's been a thing as long as the heatmap has existed. The only recent change was around a16 when torches and candles were coded to generate heat.
Also fairly recently i think they added screamers triggering off Mining the metal ores (Iron/Lead) so if you are mining in the bunker then you could get some unsavoury visitors. I think you are safe if you are mining stone, coal, or Nitrate though.
Generally speaking, their detection range is about 30-35 meters. So if you are more than 35 meters from the surface, screamers will not detect you when they come hunting. They will still come because the heatmap is infinitely vertical, and when the heatmap hits 100 a screamer scout is spawned to investigate. I usually leave some kind of defensive measure above ground to deal with them.
If you're going to have a lot of things running, it's good to spread them out a bit. Heat is generated inside the chunk area. So if you have two forges that are in separate chunks, their heat will not be combined. It would be like only having one. A chunk is 16x16 blocks.