Propane and natural gas can be used to fuel a gas log set. When looking into buying a unit that uses natural gas or propane there are a few factors to weigh into the decision. First, natural gas is cheaper and more convenient. Because you can access natural gas with the flip of a switch it is easier to come by than propane, which has to be bought from a store and hauled home. Natural gas is also thought to burn cleaner and is generally safer. You may want to consider purchasing a gas log cleaner that you spray on the logs at regular intervals throughout the year to prevent odors and creosote buildups from occurring.
Propane is heavier than natural gas, and will pool in low spots in concrete or masonry surfaces. The natural gas will dissipate in the air. Private propane companies will deliver propane. They can set up propane cylinders, which come in varying sizes (usually 20 or 40 lbs.) for the homeowner to fill. Natural gas, however, is a public utility supplied through gas lines.
Whether you are looking into using propane or natural gas, any type of gas logs need to be properly installed by a professional to insure that they function properly. Also, although gas burns clean, you should still have the logs inspected annually for functionality and the flue system inspected for debris.