Directly heated DHW cylinders and how they work
As the name suggests, the water in this type of cylinder is heated directly. Options include a flame or an electrically operated indirect coil. A directly heated DHW cylinder is often called a hot water storage heater. It is, so to speak, a water heater and hot water storage tank in one. These appliances usually have only minimal thermal insulation – and in some cases none at all. This means they can be operated separately from the existing heating system. Directly heated DHW cylinders are mostly used for decentralised DHW heating. You can read more about the other features of this type of cylinder and when it is economical to use one on the following page: Electric hot water storage heaters.