Although not as common as gas fired or electric units, oil fired water heaters of the tank variety include an oil burner and combustion chamber that vaporizes and ignites heating oil. The heat from the burner is collected by a heat exchanger coil and is used to heat the water in the storage tank. These are direct fired models. The use of oil as a fuel also permits an indirect fired water heater (described earlier) to be used. The advantage of the direct oil fired hot water heater is that it is capable of achieving hotter water temperatures and has a very high recovery rate. They do require regular maintenance and depend on the delivery and storage of fuel oil.