I don't think the balance between the two is perfect, but it's pretty good, and I've come to favor the Heat Interchange Furnace for a few reasons. Namely:
- Heat Interchange Furnaces are much cheaper than Electric Foundries (especially in Iron cost), and you need fewer of them because they smelt faster
- You don't need to build heat exchangers or steam turbines to utilize the power from the Reactor; you can convert the heat directly into smelting. This further reduces the cost needed to set them up; though, this is more of a neutral consideration, because it also means you can't use solar to power them. But if you were going to use nuclear to power the furnaces, it means you're spending much less in resources to set them up.
- I don't know if this is intentional or not, but I've noticed that Heat Interchange Furnaces do not generate pollution; they say they do in their tooltip but they don't once they're placed. This means less aggression from bugs, and fewer air purifiers necessary to dampen your cloud.
They do have some downsides; their shape makes them kind of awkward to use with beacons, and they are missing that 10% productivity. But they are much cheaper to set up and they smelt considerably faster (it's ~30% at base, but once you start putting modules on them, the difference in base productivity makes it only ~15-20%). If they get changed, I would think their crafting speed could get bumped up to 4.5.
