The Joule Stelflow unvented cylinder is designed to work with any air to water heat pump. The Joule hot water cylinder takes energy from the air to water heating system and heats the water in the cylinder through its high efficiency coil. By using a renewable energy source it helps to lower your carbon footprint.Stelflow cylinders have carefully been constructed using quality components and has been designed with performance in mind. Using our many years of involvement within the hot water industry and our knowledge of bringing unvented cylinders to the market we have created a new standard in unvented water storage.