Your oxygen tank should be replaced every three years or when it becomes too old or damaged to continue providing adequate levels of oxygen. If you wear your mask regularly and take care of it like any other piece of equipment, it should last for at least three years. An older tank may not deliver enough air flow to your face for you to feel comfortable wearing it, while a new tank may be more efficient than another person's older unit. These are factors beyond your control that could influence how soon you need to replace your tank. A trained technician who performs maintenance on an outpatient basis uses physical tests as well as visual inspections to determine whether your tank needs replacing. They will also tell you if any parts need to be replaced before they go out of warranty. Your manual should detail the manufacturer's warranty and instructions on how to take care of your unit.