Direct cylinders were first designed to be used alongside solid fuel appliances and copper back boilers. Today direct cylinders are more commonly used where the economy 7 tariffs are in use.
Vented cylinders are available in different grades – 1, 2, and 3. The grade determines the thickness of material required to make the cylinder and thus 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.