G4/AS1: Ventilation

G4 VENTILATION ACCEPTABLE SOLUTION G4/AS1 Gas-fuel appliances Part 3. Gas-fuel appliances 3.1 Natural ventilation 3.1.1 Natural draught and permanent venting 3.1.1.1 Natural ventilation systems for appliances burning gas fuel designed to operate under natural draught conditions shall: a) supply air under equal pressure conditions to the burners and to the draught diverter (i.e. in the same room and as close as possible to the appliance); and b) for non room-sealed appliances having a combined gas input exceeding 1 kW for each m3 of the space in which they are installed, be provided with vents, in addition to the ventilation required by Section 2.1 and Section 2.2. The vents shall be sized and located according to Subsection 3.1.2. 3.1.1.2 Domestic gas cookers in non room-sealed spaces that are also used for sleeping require permanent venting to the outside. The size of the vent shall be appropriate to the gas input to the cooker and shall be subject to specific design. 3.1.2 Vent sizes 3.1.2.1 Two permanent vent openings, one high level and one low level, shall be provided and each must have a free ventilation area per kW of gas input (of all appliances in the space) of no less than: a) 1200 mm2 for spaces vented directly to the outside; and b) 2300 mm2 for spaces vented via adjacent spaces. 3.1.2.2 The free ventilation opening areas may be halved for plant rooms and boiler rooms infrequently occupied by people. 3.1.2.3 Vent openings shall have vertical dimensions of no less than 50 mm, and no dimension of less than 6.0 mm in any other direction. 3.1.2.4 Low-level vents shall have their lower edge no more than 100 mm above floor level, and upper- level vents shall have their lower edge no less than 75 mm above the top of the draught diverter relief opening. 3.1.2.5 A louvred door is also an acceptable method of ventilation provided the bottom of the free area extends to not less than 100 mm above the floor, and the requisite high-level free area is available from the level of 75 mm above the draught diverter relief opening. 3.1.2.6 In plant room or boiler room installations, low- and high-level vents may be combined into a single opening, provided it reaches from floor to ceiling and has a total free area equivalent to that required for the two separate vents. 3.2 Mechanical ventilation 3.2.1 Mechanical ventilation systems 3.2.1.1 When mechanical ventilation is used, the system shall have either: a) mechanical supply with mechanical extraction; or b) mechanical supply with natural exhaust. 3.2.1.2 A mechanical ventilation system shall: a) for each kW of gas consumption (of all appliances in the plant room), provide outdoor air at the rate of: i) 3.6 m3/h for forced or induced draught appliances, and ii) 7.2 m3/h for appliances with atmospheric burners; and MINISTRY OF BUSINESS, INNOVATION AND EMPLOYMENT 28 JULY 2025 Page 13