Our propane gas was stored in a roof mounted tank that had a capacity of 500 liters. The manufacturer claims that the tank life is 15 years. Ours was over 22 years old, so it was replaced. Rooftop residential tanks are available in either 500 liter or 1000 liter sizes. The new gas tank has a capacity of 1000 liters to provide longer backup storage.
Gas is used for the stove, two hot water heaters, a clothes dryer, and several wall heaters and fireplace logs. The distribution system for gas is shown below. The tank pressure varies with temperature and will be between 100 and 200 psi. Regulators are used to reduce this pressure to 11 inH2O (0.4 psi) which is the normal operating pressure for most appliances.
There are several methods for measuring/estimating the rate of gas consumption. These are discussed in the page Propane Measurements. The easiest method uses the estimates derived from tabulating the BTUs per hour for each appliance, then estimating the hours of use per day. Propane has an energy density of 20,117 BTUs per liter, so the BTUs per day are divided by 20,117 to get the consumption in liters per day. The results are shown in the following table.
Propane use is higher during the three winter months December through February due to the use of the Rinnai heaters and fireplace log sets. For survival, only one hot water heater and the range would be used for about one hour per day each. This results in a low usage of 2.13 liters per day. If the 1000 liter tank is refilled whenever it reaches the 50% level, there will be enough gas to last for 500/2.13 or 235 days or more than six months. With a 500 liter tank, this would be only three months.
For a number reasons the propane usages in our house was felt to be too high. One of the suspected reasons (which turned out to be untrue) was that there was a propane leak. Considerable effort was spent attempting to track this down and is discussed on the page Propane Leak Detection.