I’ve lived in several houses with variations on oil heating, and noticed that the oil tanks were sized so that you needed to refill at least every year. In cases of emergency, wouldn’t it be better to have significant reserves of fuel? I mean, perhaps the reason things are so is because fuel tanks are large, ugly, and expensive(?). Does anyone know if fuel oil cannot be stored indefinitely?
Fuel oil, of itself, doesn’t degrade. However, over time it will become contaminated with water and any corrosion products in the system. That, plus the cost and physical size of tanks, make it advisable to place a practical size limit on the tank. Fuel oil with additives (AKA diesel fuel) probably has a actual storage limit due to breakdown of the additives.
Oil supply services are supposed to monitor oil usage and make sure you never get much closer than a month or so from running out. This takes care of emergencies.
Fuel oil left standing over months will often develop all sorts of bacteria which decompose it and should be treated with biocides beforehand. This and other factors make it advisable not to store it longer than necessary.