Can I use the Chimney Heights Memorandum to determine the stack height for room-sealed boiler flue systems?
Room-sealed boiler flue systems are occasionally used on small to medium sized plant. The boiler room is sealed to prevent the passage of air from anywhere except a single inlet. This inlet is a concentric tube running up the outside of the main boiler flue and terminating a short distance below it. The objective of this arrangement is to provide a form of balanced flue. Since the combustion air inlet and the flue outlet are close together it is possible, in principle, to avoid the large fluctuating pressure differences between them that can occur in conventional boiler systems in strong winds.
The Chimney Heights Memorandum (HMSO,1981) may be used to determine the required stack height for room-sealed boiler flue systems. Room-sealed boiler flue systems for boilers greater than 366.4 kW thermal input discharging at heights less than those required by the Memorandum might create local exceedances of the prescribed air quality objective for nitrogen dioxide (NO2).