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Posted by Doug Criner on October 16, 2008 at 18:28:18:
I have an older, steel, fire-tube, hot-water boiler (natural gas fueled). Works fine. But...
With a hand-held flue-gas analyzer, the excess air is around 170%. The flue-gas temperature is about 290 deg F (with 145 deg aquastat setting). This corresponds to a boiler efficiency of 78%.
I've got some work to do to get the excess air down to 20%, or so, which should improve the boiler efficiency to about 83%.
Thise boiler is natural draft, exhausting into a 30+ ft stack (considering the basement and the chimney height above the roof line). Draft is supposedly controlled by two automatic barometric dampers, admitting air from the basement, into the boiler's outlet flue - which are certainly out of adjustment.
I'm wondering just how low I can expect to get the excess air under such an arrangement? Besides adjusting the barometric dampers to reduce boiler draft, what else can I do? I hate to put a manual damper in the exhaust flue before it enters the chimney? I might be able add a damper to throttle the inlet air to the boiler?