A fireplace is a structure made of brick, stone or metal designed to contain a fire. Fireplaces are used for the relaxing ambiance they create and for heating a room. Modern fireplaces vary in heat efficiency, depending on the design. Historically they were used for heating a dwelling, cooking, and heating water for laundry and domestic uses. A fire is contained in a fireboxor firepit; a chimney or other flue allows exhaust to escape. A fireplace may have the following: a foundation, a hearth, a firebox, a mantelpiece; a chimney crane (used in kitchen and laundry fireplaces), a grate, a lintel, a lintel bar, home overmantel, a damper, a smoke chamber, a throat, a flue, and a chimney filter or afterburner. On the exterior there is often a corbeled brick crown, in which the projecting courses of brick act as a drip course to keep rainwater from running down the exterior walls. A cap, hood, or shroud serves to keep rainwater out of the exterior of the chimney; rain in the chimney is a much greater problem in chimneys lined with impervious flue tiles or metal liners than with the traditional masonry chimney, which soaks up all but the most violent rain. Some chimneys have a spark arrestor incorporated into the crown or cap. Organizations like the United States Environmental Protection Agency and the Washington Department of Ecology warn that, according to various studies, fireplaces can pose a significant health risk. The EPA writes “Smoke may smell good, but it’s not good for you. Masonry and prefabricated fireplaces can be fueled by wood, natural gas, biomass and propane fuel sources. Ventless Fireplaces (duct free/room-venting fireplaces) are fueled by either gel, liquid propane, bottled gas or natural gas. In the United States, some states and local counties have laws restricting these types of fireplaces. They must be properly sized to the area to be heated. There are also air quality control issues due to the amount of moisture they release into the room air, and oxygen sensor and carbon monoxide sensors are safety essentials. Direct vent fireplaces are fueled by either liquid propane or natural gas. They are completely sealed from the area that is heated, and vent all exhaust gasses to the exterior of the structure.