Non pressure thermosyphon system are used to heat water for household, functioning optimal during March-November or when the outside temperature is more than 4-50 ℃ Can absorb heat in case of diffuse radiation (when the sun is overcast) It is constructed from individual vacuum tubes type thermos that transferring solar radiation by convection. Because the tubes are constructed in this way they have 2 important functions to isolate the heat and increase absorption thermal of solar radiation. Tank is mounted together with the vacuum tubes on a metal support.