Chimneys operate on the principle that hot air rises above cold air. Mounting brass hood on fireplace surface. Firebox Diagram Masonry Fireplace Masonry Fireplace This process results in a draft, or a balanced flow of hot gases and smoke, up and out of the fireplace’s chimney. How does a fireplace work diagram . Some fireplace units incorporate a blower, which transfers more of the fireplace's heat to the air via convection, resulting in a more evenly heated space and a lower heating load.fireplace efficiency can also be increased with the use of a fireplace fireback, a piece of metal that sits behind the fire and reflects heat back into the room. As that air rises, more heated air from the fire is pulled after it. The size of the firebox dictates how much wood can be added to the fire and influences how much heat can be generated. Electric fireplaces are the best way to add the warmth, comfort, and ambiance of a fireplace when venting is not an option. The thermopile ...