| ||The continuous-flow principle heats water as needed, only heating the water you use. Dux Endurance® Plus models in 16, 20, and 26 litres feature an all-weather cover. Endurance Premium features a stainless steel cover. Anti-frost feature is standard on all models and protects the unit from damage during very cold temperatures. Range of delivery sizes 16, 20, & 26 litres per minute models all available, allowing you to select the current model to suit your hot water usage needs. 5 Star energy rating, very efficient use of gas, reducing running costs and saving natural resources.