Water heaters with wet heater

Wet heater

— the so-called wet electric heater is a metal (usually copper) tube, inside of which there is a heating filament and an insulating filler with good thermal conductivity. Compared to spirals, wet heaters are somewhat less efficient (in particular, they heat up more slowly), but they are much more durable and more resistant to emergencies (for example, heating without water or air pockets). A clear disadvantage of wet heaters is the tendency to form scale.