Help- Smoke Pipe Slope .Vs. Ash Problems?

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Post Thu. Sep. 04, 2008 8:57 am

Longtime lurker/new member here, and I am puzzled and seek advice about seemingly contradictory information.

As I understand it, there seem to be two schools of thought about smokepipes for coal stoker boilers. Some say that the pipe should slope slightly upwards to the chimney on horizontal runs. This is what is done normaly on oil burner boilers.

Others say the pipe should be horizontal or the fly ash that settles in the pipe will go back/fall back into the boiler.

Can anyone shed some light on this apparent contradiction?

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Post Thu. Sep. 04, 2008 9:03 am

IMO, it's always better to have some rise to the pipe as it makes its way to the chimney. If it's a short run, it doesn't matter much. Fly ash will settle at the low point. Make a provision to clean it out by using a "T" instead of an elbow. You can just remove a cap from the "T" and cleanout the fly ash.

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Post Thu. Sep. 04, 2008 9:15 am

Hello Orvis, welcome to the forum. There are different coal burning units with diriections and needs for the flue..

All chimney flue pipes should have a slight uphill slant towards the chimney.. The units you read about that have statements about the fly ash are the AHS boilers, and they are a 'different animal'. This boiler has a fan-forced exhaust, and has a cyclone-ash separator in the boiler.. if you have too tall of a vertical stretch out of the boiler, the fly ash that made it through the separator would drop back into the boiler's 'ash cone' and potentially plug it.. AHS wants a horizontal [a slight uphill slope will make zero difference] above the breech to collect any flyash suspended in the exhaust when the fan stops.

Greg L.

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Post Fri. Sep. 05, 2008 10:38 pm

The uphill slope is to maintain gas speed, it has nothing to do with the ash. That is why wood, oil and gas burners have the slope too. A level pipe will lose a lot of gas speed, and fill with ash quicker. It is better to carry the ash to the chimney with the extra speed. Then it just drops to the clean out at the base when the gas turns to go up the chimney.

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Post Fri. Sep. 05, 2008 11:25 pm

I go with the up hill all the way idea if you are using a natural draft stove or boiler or whatever. In my experiences fly ash sticks to the pipe throughout the run but the highest amounts of ash I usually see in the elbow by the stack opening and at the base of the chimney.

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