With roof mounted systems, the tank is directly above the collector panels. The Thermosiphon principle is based on two naturally occurring phenomena, dark objects absorb heat and hot water rises.

Hot water is lighter than cold water, so it naturally flows up into the tank (or rather gets pushed up by the colder water sinking down).

Water flow happens through the mains pressure. As hot water is taken out (from the top), new cold water flows in and gets heated up in the panels.

Using these natural physical laws makes it reliable and cheap to run.The disadvantages: You might not like the look of the tank on the roof.

There are also some situations were the hot water would need to travel too long before reaching your shower. In such cases, a lot of water is wasted and we recommend the split systems.