Tubular heater, 8,5 mm diameter, of special steel 1.4571, with supporting handle, protection mode IP 67, hose proof, lead-in 3 x 1,5 sq. mm, with plug with earthing contact (up to 3 KW), as well as holding clip. The heater is to be introduced into liquid in a suspended vertical position, using the holding clip, while the liquid level must not be lower than the minimum depth of immersion.