The tank is designed to accumulate hot water from various heat sources. The R-Series tank improves the hot water supply system flexibility, allowing you to accumulate a constant volume of hot water and use hot water supply recirculation to increase comfort of use. And the possibility of connecting an electric heater via a 2″ (for 750 and 1000 litre tanks) or 1 1/2″ (for up to and including 500 litre tanks) hole with internal thread in the bottom of the tank makes the tank more versatile.