Smokestack - Momo-Softworks/Cold-Sweat GitHub Wiki
The Smokestack is a utility block used to enable the temperature-controlling functionality of the Icebox and Boiler. It can be considered a pre-Nether alternative to the Hearth.
When placed on top of an icebox or boiler, it will insulate a small (16x16x16 blocks) area, up to a maximum volume of 1500 blocks.