Instead of (or maybe in addition to) checking that the tile entity inherits from minecraft's furnace block, it would make sense to have a tag—might i suggest supplementaries:furnace—that marks a block as one that the bellows should speed up.

I can do both for max compatibility. That will also mean that the tag will be left empty for mod pack makers to add stuff to

Yeah, that sounds ideal, thank you.

wouldn't it be better if I were to add the same functionality to the mod config? I thought that way it would be easier to use

I suppose that works too, but a tag lets other mods add support for the bellows on their own, without having to inherit from the vanilla furnace. This is a pretty common use case for tags, actually.

I guess that makes sense, I'll add it then. I haven't really learned how to properly use tags, that's why I was asking.

Yeah, tags are really useful for both mod compatibility and configuration. They're usually used for recipes and such, but they can be useful in other ways.

To give specific examples, Create has a couple of tags that are used by Farmer's Delight to make its stuff behave in certain ways when Create is also installed:

• create:upright_on_belt (an item tag) makes items stand up on conveyor belts rather than lying flat; Farmer's Delight adds this to its milk bottle so it stands up just like the vanilla water bottle.
• create:fan_heaters (a block tag) makes a block usable as a heat source for create's bulk cooking recipes, and Farmer's Delight adds this one to its stove block.

I hope that helps!

it does, thanks. At the end I've added both a config and a tag to have the best of both words. I would have added a tag only if there was a vanilla or forge "furnace" tag. they have one for campfires but not one for those, how strange

Awesome, thank you