The principal of the thermos flask is widely known. Here the multi-valve collectors have been replaced with borosilicate glass tubes that are built in the same manner as the thermos flask. The outer layer is exposed to the atmosphere, which permits light to pass through. It passes through the vacuum between the two layers of glass where it strikes a blackened surface and is converted to infrared radiation that now has no escape.

The inner tube heats up and by conduction it is transferred to the water within. Water in the collector rises as it heats. At the same time, in a state called laminar flow, where two streams of water pass one another in opposing directions, cold water sinks to the bottom of the tube. Solar water heater vacuum collectors are very efficient but still suffer some problems. As the cold water sinks, it reaches a point where conduction causes the downstream temperature to reach the same temperatures as the upstream water.

Turbulence is created preventing the water below the mixing point from ever reaching the top. Effectively this shortens the length of the collector and causes the pool below the stagnation point to rise to extreme temperatures, leading to hot spots and eventual failure. The maximum length of tubes for this type of system should be restricted to about 1 meter to avoid problems. This restriction limits the amount of heat that a solar water heater can produce in one day.

The vacuum tube collector does, however, offer many advantages over conventional systems. Heat cannot be convected or conducted across the vacuum because there are no atoms to perform either function and the tubes, being round solve the light issues inherent in any flat plate system.

In spite of the limitations presented above, this device is far superior to any conventional system.