Well, 0 is arbitrary in Celsius and especially Farenheit, so doubling that temperature isn't really doubling the heat.
Kelvin has its scale actually designed around how heat energy works. 160F is 344K. Double that and you've got 688K. Convert that back to stupid-units and you have 779°F
I think I did that right, at least. If nothing else it shows how whacky temperature math can be when doubling units gets wildly different results!