Flueless Gas Fires do not need a flue – as the name suggests. This makes them more flexible than standard slim line Gas Fires which need a chimney or a pre fabricated flue to work. Flueless gas fires clean the harmful air by using a catalytic converter by converting them into nothing more than carbon dioxide and water vapour. Flueless gas fires are marketed as 100% efficient fires, as no heat is lost up the chimney. The average gas fire is only 60% efficient. All flueless gas fires need a minimum room size (which depends on the fire selected), and need an air brick (through-wall ventilators) to be installed in the room where the fire will be fitted.