PROVISIONS WHICH APPLY GENERALLY TO COMBUSTION INSTALLATIONS J O N L I N E V E R S I O N J Diagram 9 Ventilator free areas Equivalent or Free area 1 Equivalent or Free area 2 (a) Ventilator assembled on site from components The ventilator area is the smaller of equivalent area (1 or 2) (as declared by manufacturer), free area (1 or 2) (as measured in (b)) or the duct area.
Permanently open air vents 1.12 Where ventilation is to be provided via a single proprietary assembly, for example when it is proposed to use a proprietary ventilator with integral grilles to bridge a cavity wall, the equivalent area of the ventilator should be taken as that declared by the manufacturer having been measured by the method in BS EN 13141-1:2004. 1.10 Permanently open air vents should be non-adjustable, sized to admit sufficient air for the purpose intended and positioned where they are unlikely to become blocked. Ventilators should be installed so that building occupants are not provoked into sealing them against draughts or noise.
Ventilation openings should not be made in fire-resisting walls other than external walls (although they should not penetrate those parts of external walls shielding LPG tanks). Air vents should not be located within a fireplace recess except on the basis of specialist advice. 1.13 Where two or more components are to be used to provide a non-proprietary assembly, the assembly should be kept as simple and smooth as possible. The assembly should be taken to have an equivalent area equal to that of the component with the smallest equivalent area in the assembly.
1.14 The equivalent area stated in the ventilator manufacturer’s literature or marked on the air vent should be used whenever it is available, as this can differ considerably from the free area measured at one end of the air vent. When this is not available the equivalent area of a simple ventilator with no internal baffles can be taken as the total unobstructed cross-sectional area, measured in the plane where this area is at a minimum and at right angles to the direction of air flow. For an airbrick, grille or louvre with apertures no smaller than 5mm, it will be the aggregate free area of the individual apertures as shown Diagram 9.
1.11 A way of meeting the requirement would be to size permanently open air vents so that their equivalent area is sufficient for the appliance(s) to be installed (taking account where necessary of obstructions such as grilles and anti-vermin mesh), and to site them: a. outside fireplace recesses and beyond the hearths of open fires so that dust or ash will not be disturbed by draughts; and b. in a location unlikely to cause discomfort from cold draughts. 19 Approved Document J Combustion appliances and fuel storage systems O N L I N E V E R S I O N