An electric kettle rated $1000\ \text{W}$ heats $2\ \text{kg}$ of water from $20^\circ\text{C}$ to $100^\circ\text{C}$. Only $80\%$ of the electrical energy goes into the water; the rest heats the kettle and the air. The specific heat of water is $4200\ \text{J kg}^{-1}\,\text{K}^{-1}$. The time taken, in minutes, is ____.