Netherrack does not cook into bricks inside of furnaces. I had noticed that my furnace was cooking non-stop (like it should, its an auto-smelter specifically for this task) but when I would check the chest that it feeds into that there would be no finished product. I checked the hoppers, the chest, made sure it wasn't a render glitch that the bricks were there but not loading the number. And then when I checked the furnace itself, the progress bar to show that it was cooking did not move, but it kept feeding itself coal blocks as if it was working.