Sack of coal

From Toadwater Guide

A "Sack of Coal" and a Lump of Coal both have the same use. When they are added to a furnace, it burns hotter for a few minutes giving more experience then players would normally receive for smelting but higher odds on success. Globally this is called the Edict of Hot Coal.

Every time coal is added to the furnace, it fills the space up by one unit. To empty the furnace, it has to be dug out with a shovel with higher power or equal to the space already dug out. Digging with a shovel burns the shovel. The time for a Lump of Coal is three times the amount of units dug out, in seconds.

Example: If 40 units of space has been dug out, adding one coal would activate the edict of Hot Coal for 120 seconds and fill the furnace to 39 units of space. The next piece of coal would add 117 seconds. It would take a level 38 shovel or higher to dig out a unit of space.