Free areas of permanently open air vents for gas appliance installations

Appliance in a room or space or appliance compartment ventilated via an adjoining room or space or appliance compartment ventilated direct to outside: Open-Flued: A = 500 mm² per kW input (net) B = 1000 mm² per kW input (net) C = 2000 mm² per kW input (net) Room-Sealed: A = 500 mm² per kW input (net) D = 500 mm² per kW input (net) E = 1000 mm² per kW input (net) F = 1000 mm² per kW input (net) G = F H = 500 mm² per kW input (net) J = H No vent needed for certain room-sealed configurations. Notes: 1. A, D, E, H and J are permanently open vents to the outside. B, C, F and G are permanently open vents between an appliance compartment and a room or space. 2. Calculations employ the appliance rated net heat input. 3. The area given above is the free area of the vent(s) or the equivalent free area for ventilators of more complex design. 4. Vents at C, E, G, and J are low level vents. Vents B, D, F and H are high level vents. 5. In older dwellings with an air permeability which is more than 5.0 m³/h/m² the first 7kW (net) can be ignored.