How do you bleed air from an old radiator?

To bleed an old style radiator, you’ll need to locate the bleed valve. This is typically located at the top of the radiator, on the left or the right. It is usually marked with a square-shaped screw. You’ll need a matching key for the bleed valve. Turn it gently and gradually until you hear a hissing sound. Stop when water is released from the valve.