Posted By John Webster Robert The Gas Safety (Installation and Use) Regulations (GSIUR)1994 as updated 1998. Many instant water heaters, and other appliances, either vented into the room or could if the flue was obstructed. If the gas/air mixture was incorrect, highly toxic carbon monoxide gas could build up in the room, resulting in some 200 deaths per year. The problem was exacerbated in bath/shower rooms where very powerful units were often installed in small rooms in which, to avoid draughts, there was little ventilation. The regs state that only 'room-sealed' appliances may now be installed in a room used or intended to be used as a bathroom or shower room. Furthermore, 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. No instantaneous water heater be installed in any room, unless it is 'room-sealed' or fitted with a safety control device. 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. I understand that Ascot is no longer involved in the water heater market, although there are plenty of other manufacturers of modern instant water heaters around. John