Power needed to generate for heating strip - Nichrome strip element
8mm x 0.25mm = 2mm2, which is "roughly" the same resistance as 14AWG. According to the calculator at Jacobs Online, 1m of 14g Nichrome 60 produces "roughly" 270&deg;F from 22.3W (3.5V x 6.37A). 

But heat is not temperature. The wattage above applies when cutting expanded polystyrene foam. In still air the wire might get less cooling and need less power. But flat strip has more surface area than round wire, so it may get more cooling and need more power - unless wound in a helix when it may need less power. But if attached to something that acts as a heat sink it will need more power, etc.

Without knowing the parameters of the thermal environment a definitive answer isn't possible, but hopefully this "rough" estimate is close enough to provide a starting point.