high efficiency vacuum tube Solar water heater 1,high heating efficiency 2, easyly installation 3. energy-saves high efficiency vacuum tube Solar water heater ... Specification:1) Vacuum tubes: Φ47 x 1,500mm, Φ ... 58 x 1,800mm, Φ70 x 2,100mm2) Vacuum tube size: 15, 16, 18, 20, 24, 26, 28, ...