A gas fireplace uses either natural gas or propane to produce heat. In some ways, a gas fireplace is similar to a gas furnace, but they use slightly different systems and have different goals. A fireplace is used as a decorative piece as well as for heat and can be located in different places throughout the home. Each gas fireplace can be separated into basic parts.
The gas line channels the natural gas or propane into the fireplace. This line ends in a valve that keeps the gas shut off when the fireplace is not used. When you turn a gas fireplace "on", you are opening this valve and allowing the gas to be lit by the pilot light.
The ignition system of a gas fireplace is a part of the gas line and ensures that the gas ignites when it enters the fireplace. Ignition systems are typically pilot lights. An electric igniter creates a spark that lights a small amount of gas which perpetually enters the fireplace. This light gas will then light entering gas from the main valve. You will need to shut the pilot light off during warm seasons to save money.
The firebox is where the gas is burnt in the fireplace. The firebox is made from fireproof materials, usually metals, that are joined together so they are airtight. The firebox has a glass front on it: in traditional fireplaces this glass door can be opened, but in gas models the fireplace is typically sealed to prevent exhaust from escaping into the room. Inside the firebox are synthetic logs and coals to make the fireplace look more natural.
Most gas fireplace models also have a venting system, which accomplishes two main tasks: It provides the firebox with oxygen, allowing the flames to burn more easily; and it allows the small amount of dangerous exhaust fumes the gas creates to escape. Venting systems are typically simple metal pipes, layered for heat protection, that connect the firebox to the outdoor air.
Gas fireplaces do not always have fan systems, but those that do not cannot heat rooms effectively. The fan systems use an electric motor to turn fan blades that cycle air around the firebox when it absorbs some of the heat from the fire.