Just curious, how could they tell the furnace was seven times hotter? In a typical furnace, there would be a peak temperature. In an air introduced furnace, there could be three recognized temperatures, of black, orange red, and white, based on a piece of iron within.
But the other four temperatures would be difficult to determine. Perhaps an estimate based on the amount of fuel used.
Well, that was his order.
Whether they achieved it or not is another matter.