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Posted by powereng on January 18, 2002 at 00:38:20:
In Reply to: draft posted by afdmello on November 22, 2001 at 05:00:10:
natural draft is the pressure difference caused soley by the hotter flue gas going up the stack as you know hot air rises and this causes air to be sucked in at the boiler
forced draft is used only up to a point where there is too many things in the furnace like economiser, super heater , air heater, baffles all of these create resistance for the air to escape out of the stack therefore it will create a positive pressure in the furnace that is when you need an induced draft fan to suck while the forced draft fan blows the air out the stack. induced draft alone is rarley used. package boilers normaly use forced and larger water tube boilers use ballanced which is both ID & FD