Vent free fireplaces are fireplaces that do not require any type of vent system. Instead, they are designed to burn clean and the combustion by-products allowed to flow into the room the fireplace is located in. Stringent requirements ensure that these fireplaces not only burn cleanly, but that they are located in rooms of sufficient size to ensure an adequate supply of fresh air is always available for the combustion process. A highly sensitive sensor is employed to turn off the gas to the fireplace should the level of oxygen within the area begin to deplete. The most obvious benefit of this type of system is that no heat is lost through the venting system making the fireplace virtually 100% efficient. Currently, these type of gas fireplaces can only be installed in some areas of the United States. They are not approved for use in Canada.