(Source: Packaged Firetube Boiler –Engineering Manual-―, American Boiler Manufacturers Association, First Edition, page 35) Circular elbows should be of a minimum of four piece construction and have a minimum R/D ratio of 2.0 where R is the centerline radius of the arc and D is the diameter of the duct. ―Changes in direction should be accomplished as gradually as possible. Breeching Turns – From turns as small as 30° up to 90°, the design of the turn can have a major effect on the boiler’s operation. The breeching must be installed with a slight upward pitch toward the stack to ensure it is self-venting.Ĥ. Round ducts are more efficient, and the large flat sides of square or rectangular ducts contribute to noise caused by resonance. They should be constructed of round ducts only. Breeching – When required, the breeching should be as short as possible. These problems are more difficult to find if the high and varying winds are created or amplified by the buildings located at the site.ģ. Stack Exit Location – A stack exit that is located in an area where it is subject to very high and varying winds can create operational problems that appear to have no logical explanation. These conditions can change from winter to summer, day to night, and sometimes day to day.Ģ. Cool ambient temperatures can chill flue gas products and reduce or eliminate draft conditions that existed with warmer ambient air. This can cause burner stability problems after the system has warmed to operating temperatures.Ī very high stack that does not have some type of insulation, in addition to the problem listed above, can have widely ranging draft conditions caused by changes in the ambient air temperature. (Source: Packaged Firetube Boiler –Engineering Manual–, American Boiler Manufacturers Association, First Edition, page 28)Ī very high stack can create a high back pressure (a high positive pressure at the boiler stack connection) that the burner must overcome which may turn into a high draft (a high negative pressure at the boiler stack connection). Stack Height – The stack or chimney should be of sufficient height to extend above the roof of the building or adjoining buildings to avoid down drafts in the stack or the possibility of carrying down combustion gases to undesirable locations such as air inlet ducts or open windows in adjoining or nearby buildings. Improper exhaust system designs can cause problems that come and go, or can vary with stack temperature, ambient temperature, wind conditions, operating status of other boilers connected to the exhaust system, and many other varying conditions.Ī few of the problems to check in the event of an erratic operations and/or problems that appear to have no solution are:ġ. Other Stack Configurations can be used if they are properly engineering. Packaged firetube boilers are designed to operate at their peak performance with short, straight flue stacks. This will avoid many problems that are too often considered combustion related but are really system generated, resulting from improper flue gas breeching and stack design. Refinements in combustion technology and burner designs have made it more critical that everyone reviews the total system to ensure proper operation. Each item affects how well the other items perform their task. Firetube boiler and burner packages with the exhaust stack and breeching attached to them operate as a system. Johnston products have been designed for maximum efficiency.
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