... 65% heat increases 12% Higher temperature, more hot water Three target vacuum tubesJust like an automobile engine, the computer CPU, vacuum ... heater. Its performance lies on the coating technology, The three-target evacuated tube rise the heat more than 12%. 1) High ... 2.Evacuated Tube Basic Specifications. 1800*58mm/1500*47mm three target solar vacuum tubes,vacuum tubes for solar water heater