To enable the evacuated tubes working perfectly even in sub-zero temperature, aluminum fins and copper heat pipe is inserted in the evacuated tube in such a way that all the heat absorbed by selective coating is transmitted to the heat transferring fluid inside the copper pipe. This enormous heat is then transferred to the water inside hot water tank with the help of condenser. This type of tube is called heat-tube. The whole solar water heater with heat tube collector is designed in such a way that water never enters the evacuated tube. This feature enables these SWH to produce high temperature hot water even in freezing outdoor temperature, without having the tubes damaged due to high internal and external temperature difference.