Speed Upgrade: Increases speed and fuel consumption.
Efficiency Upgrade: Decreases fuel consumption.
IO Upgrade: Enables automation. I=Input, O=Output, F=Fuel.
X means, nothing can enter or leave this side.
Check mark means, you can input and output with hoppers, itemducts, pipes, etc.
A means, the furnus/pulvus pulls/pushs by itself. It includes the check mark.
Without IO Upgrade you can insert/extract items like a vanilla furnace.
Slot Upgrade: Adds one additional input slot and output slot (max. 2).
XP Upgrade: Increases XP output.
Eco Upgrade: Keeps the heat even if there are no items in input slots and prevents that the progress bar will be reset if the furnus/pulvus is out of fuel.
Energy Upgrade: Enables energy support.