Most people are going to know which gas to use. However, for those that do not, here is the choice:

NATURAL GAS is more commonly found in new construction and in more developed areas. If you already have natural gas running to your home or building, it is probably more cost effective to have a gas line professional run a line to your fireplace or room where the gas fireplace, logs, stove or heater will be used. Natural gas yields about 1000 BTUs per cubic foot.

LP (also called propane) is effective for those that do not have ready access to natural gas, in rural localities, if there is a desire for the appliance to be semi-portable, or if some sort of central propane supply tank is available. Propane tanks should always be stored outdoors in a way to avoid extremely high temperatures. Propane is sold by the pound (or gallon) and delivers 21,560 BTUs per pound (or 91,500 BTUs per gallon.) It yields about 2,500 BTUs per cubic foot (vaporized).

NOTE: We often have people ask about converting a unit from one gas to another. The hoses, lines, control valves, and orifices on burners for each gas are quite different in size. Many grill manufacturers, and other gas appliance manufacturers, offer conversion kits for some items. However, vent free appliances cannot be converted. Propane is roughly 3.5 times heavier than natural gas therefore its regulators, gas jet orifices and even its control valves are often different versus and the same piece of equipment using natural gas.

NEVER ATTEMPT TO ATTACH A PROPANE GAS SOURCE TO ANY NATURAL GAS APPLIANCE. THIS WILL RESULT IN FLAMES 2-4 TIMES HIGHER THAN IS CORRECT AND COULD BE A VERY DANGEROUS, LIFE-THREATENING FIRE HAZARD.

Attaching natural gas to a propane appliance is of little good. The pilot light probably won't even light.