Simple Tank in Tank Container

The basic Tank in Tank has no coil. The boiler, or any source that shares the same water as the heating, connects directly to the outer buffer tank; the radiators draw water from the same tank, and the inner cylinder is heated by the water around it.

It is the simplest form of the solution, for installations with one main heat source such as a wood or pellet boiler. It can also take an electric immersion heater as backup. If you plan to add solar collectors later, look at the models with a heat exchanger.