World Heat Copper Vented Indirect Grade 3 Foam Lagged Cylinders
Indirect copper hot water cylinders are designed to work in conjunction with central heating systems. Heat is transferred from the boiler to the water contained in the cylinder via a heating coil. Vented hot water cylinders are available in different grades - 1, 2, and 3. The grade determines the thickness of material required to make the cylinder, this then determines the amount of pressure the cylinder can withstand.
They are usually size on a "working head" in meters which means the height difference between the cylinder and the header tank usually in the loft.