Built-In / Zero Clearance: Zero clearance gas fireplaces are used in installations where there is no existing fireplace (new construction or renovation). These are factory-built metal fireplaces using a multi-layer construction (an inner & outer shell) which can safely be placed in direct contact (zero clearance) with combustible floors and walls. Inserts: A gas or wood burning unit designed to fit into an existing masonary opening or factory built fireplace. Freestanding Stoves: A stove is a freestanding unit that stands away from the wall (generally used for efficient and cozy heating. Direct Vent: A gas fueled appliance (fireplace, insert or stove) that draws all of its combustion air from outdoors and exhausts it's combustion products to the outdoors eliminating the need for a standard chimney system. A sealed glass door on a direct vent units is critical to keeping the combustion system sealed from the home, maintaining high efficiency and indoor air quality.