Direct vent fireplace

A direct vent fireplace is a prefabricated metal fireplace that is part of a direct-vent system. "Direct vent" refers to a sealed-combustion system in which air for combustion is piped from the outdoors, and the vent products are vented to the outdoors. "Direct vent" does not simply mean that all gasses from combustion are vented to the exterior of the structure in which it is installed.

The preassembled fireplace unit is made up of two main components: the outer housing, and the flue system.

The outer housing is the part of the fireplace unit that is installed in the framing of the building. Two of the main operational components are housed inside of it. The first key component within the outer housing is the firebox, which is surrounded on three sides by the outer housing, and on one side by the glass panel that faces in towards the room. This is the space in which the fire burns during operation. Because of this, the gas burners (either natural gas or propane) are located inside of the firebox. To provide a more realistic look, imitation logs and ember material are placed on top of the burners. The ember material, which will not burn, is designed so that it will glow like real embers when heated. The firebox is designed to be smaller than the outer housing so that there is an empty space between the outermost walls of outer housing and the outer walls of the firebox . The empty space in between the firebox and the outer housing is the second important operational component of the outer housing. This space is filled with air from the interior of the room being heated and is used to add hot air to the room without the addition of exhaust gasses from combustion.

The flue system is composed of two flues, the inner flue and the outer flue. The outer flue draws air into the bottom of the sealed firebox to allow for combustion. The inner flue draws hot exhaust gasses from the top of the sealed firebox and vents them directly to the outside of the structure through either an adjacent wall or the roof.

To begin the operation of the fireplace unit, the user must turn on the gas supply and ignite the burners. Once this is done, the unit will operate completely autonomously until the gas supply to the burners is shut off. While in operation, convection will cause the hot air in the firebox to rise to the top of the firebox. As the amount of hot exhaust gasses increases from the combustion process, the hot gas at the top of the firebox is eventually pushed out through the inner flue. At the same time, the removal of the exhaust gasses through the inner flue allows for relatively cold air to be drawn into the firebox through the outer flue.

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Wikipedia