During furnace processing it calls VaporizeEntity. This mod changes that to DestroyPart instead.
The end result is the furnace should have relatively the same impact as the processor does. It won't create the many particles during vaporization and you can drop a whole Mackerel in there without issue.

• Hardspace Shipbreaker obviously.
• BepInEx: https://github.com/BepInEx/BepInEx (You want the x64 version.)

• Extract BepInEx to the root Hardspace Shipbreaker folder so winhttp.dll is in the same folder as Shipbreaker.exe.
• Extract this mod so FurnacePerformanceImprovements.dll is placed like this: Hardspace Shipbreaker\BepInEx\plugins\FurnacePerformanceImprovements.dll.

BepInEx uses winhttp.dll as an injector/loader. Renaming or deleting this file is enough to disable both my mod and the loader.
Or just remove FurnacePerformanceImprovements.dll/pdb from the plugins folder.