Gas line diagrams are available at fordiagrams.info or chestofbooks.com. Fordiagrams.com is a website full of gas line diagrams, and chestofbooks.com is a website that contains not only gas line diagrams, but diagrams for other topics as well.
A typical gas line diagram on fordiagrams.com contains a diagram that includes components including the circulator pump, flue vent, relief valve, heating oil line, boiler drain valve and pressure-reducing water feeder for a heating broiler which is part of the gas line. It has different pictures that represent different items around the house that connect to the gas line. The items that usually appear on the diagram are a gas meter, a dryer, a furnace, a range, a water heater, and a fireplace if the house has one. A gas line diagram also contains important details such as the delivery pressure, gas line size, the total feet of gas line, and the total number of BTUs, which stands for British Thermal Units. Every item that is attached to the gas line uses a different amount of BTUs.
Checkofbooks.com also features a number of gas line diagrams. The only difference is that there are no pictures to represent the items that connect to the gas line.