Peltier Heat Generation and Dissipation
A peltier hot side has both the wattage of the heat your moving, and the electrical power your using to move that heat, meaning you will generally need to heat sink at least double what your feeding in to it,

The higher the temperature difference, the higher the voltage, the higher the heat flow the higher the current. It more efficient to drive a peltier with a moderately high frequency PWM or analog voltage source, as the efficiency is lower when switching it on and off from the full supply voltage.