You are asking the wrong question. There is a vacuum in the vacuum tube. In other words, the tube you see is double layered. There is a gap in the middle of the second floor.
The second layer contains water. You must have water when you use it. Once you add the water here, you will never be able to turn it off again.
Just one heat cycle.
For a family of 6, relatively speaking, choose one with around 24 tubes.
01 Huangming (famous Chinese brand, well-known Chinese brand, top ten solar water heater brands)
02 Sanle (domestic non-pickup product, top ten solar water heaters, large enterprises)
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03 Tianpu (domestic free product, top ten solar water heaters, large enterprises)
04 Qunsheng (Chinese famous brand, first line brand /brand, top ten solar water heaters)
05 Billion Home Energy (China famous brand, mbrand/first-line brand, top ten solar water heaters)
06 Sun Rain (China famous brand, first-line brand/brand, top ten solar water heaters)
07 Zhannan (Chinese famous brand, top ten solar water heaters, export famous brands)
08 Tsinghua Sunshine (Chinese famous brand, first-line brand/brand, top ten solar water heaters)
09 Li Norit (Chinese famous brand, first-line brand/brand, listed company)