Posted By John Webster Greg The Gas Safety (Installation and Use) Regulations (GSIUR)1994 as updated 1998 require that appliances with a gross heat output of more than 14 kilowatts installed in a room used or intended to be used as sleeping accommodation must be room-sealed and those of 14 kW or less must either be a 'room-sealed' type or incorporate a safety control device designed to shut down the appliance if there is a build-up of combustion products in the room concerned. By room sealed, a balanced flue arrangement is usually meant, so the air enters from outside, the combustion chamber is closed and the flue vents outside. Fireplace type gas fires are normally under 14kW, so if not room sealed a carbon monoxide detector which shuts off the gas can be fitted. You will need to check, but I don't think the legislation is retrospective ie old gas fires can continue to be used in domestic property. Nevertheless, as the sitting room is being converted to to used as sleeping acommodation, the law may apply, and of course will to any new appliance installed. In any case, the regulations represent current good practice, so on a risk assessment basis alone you would want to comply.