Flue and Stack Sizing, Location

Negative furnace pressure diminished product quality by admitting cold drafts that cause temperature nonuniformity, and may change the metallurgically required atmosphere in the furnace. Poor product quality raises fuel, labor, and material costs because the job has to be done all over again. It may cost loss of business and customers. 

The only gain from a negative furnace pressure is lowered fan or blower costs (operating and capital). 

Excessive positive pressure—more than about 0.02 in. wc (0.5 mm)—endangers people nearby, and shortens the life of furnace components. 

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