Solar Tribune

Thermosiphon Water Heater


A thermosiphon system – also called a thermosyphon solar water heater – has a tank connected to a flat plate-collector. Thermosyphon systems are passive: no pumps are needed to aid water flow.

The water tank is installed above the collector, directly on the roof. As hot water rises in the tank, cold water flows to the bottom and into the collector. The cold water directs the heated water through the collector outlet and into the top of the tank. This heated water flows from the rooftop tank to the ground-level storage tank.


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Thermosiphon systems are very efficient as they are simple and rely only on the laws of thermodynamics, allowing them to function even when mains power is down. However, these systems’ efficiency declines in colder climates.  Plus, other factors make such systems unsuitable for some households: the roof may not be able to support the weight of the storage tank, and the appearance of a fully roof-mounted system does not appeal to all property owners.

Nowadays, with the development of new technologies, the use of thermosiphon systems has decreased. Contact your installer to find out whether such a system is appropriate for your home.

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