Thanks for the feedback. I will consider reducing the concrete cost to a stone brick cost. To be clear, I didn't intend this to be an early game choice. There is no way to make the recipe require both concrete tech and flammables tech. By putting it in flammables, I ensure you have the pump, but not concrete. If I put it in concrete, then I assure you have concrete, but not the pump. So I chose pump, but either way it could never require both unless I put it significantly further down the tech tree, or made a new tech, neither of which I wanted to impose on the user. I chose flammables because it's typically likely someone will be researching flammables around when they're researching concrete, as opposed to fluid handling (where the pump comes from), which typically comes far before concrete. I also don't agree that recipes need to necessarily become available only after all of the necessary materials are available. I'd like to be more flexible than that. The tech tree is already a clusterfuck, and so there are rarely perfect decisions, without rewriting it.
The gas furnace allows you to use as many modules as the electric furnace, and so is balanced more toward that segment of the game. I've been considering removing the modules, reducing the power cost to that of a steel furnace, thus leaving it as just a gas version of the steel furnace. Then it would make perfect sense to use stone bricks instead of concrete. I'm probably sticking with the pump, though: requiring a pump is a staple throughout my gas-power mods. I wouldn't want it to be too easy. :) As it stands, this furnace is a superior option to the steel furnace due to its module slots, and only that; and this is not an advantage that matters during the early game. If you make a good argument for why it should be otherwise, I'll consider it.
