Outlines the ventilation requirements for new or replacement gas appliances for non-domestic or domestic purposes utilizing 1st, 2nd or 3rd family gases which carry the CE mark and with a rated heat input not exceeding 70 kW based on net CV. Excludes LPG installations covered by the requirements of BS 5482-2 and installations with all gases covered by BS 5482-3; gas installations in caravans, holiday homes or residential park homes constructed to conform to BS EN 721 or BS 5482-3 which were installed at the time of construction; decorative fuel effect gas appliances of the type covered by BS 5871-3.