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"Simple" Draft Inducer

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Hunderliggur, Dec 26, 2010.

  1. Hunderliggur

    Hunderliggur Minister of Fire

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    I am looking for a simple draft inducer solution for my boiler with double wall pipe. Based on my loading opportunities, I often feed the fire when there is still wood left, so I have smoke when I open the loading door. Waiting until it is almost burned out is not an option. My exhaust is double wall pipe in the room connecting to triple wall in the attic and above the roof. Out of the back of the boiler I have a Tee with exhaust above, automatic damper horizontal and cleanout cover on the bottom. I was thinking of a Venturi system where I put a length of 1 1/4 or 1 1/2 copper pipe (have some left over from plumbing) about three feet up the flue through the bottom plate, then attaching a 4" 200 CFM draft inducer fan (4" Inline Duct Fan model M-4) to the lower end of the pipe. I would turn this on when loading (I don't have any induction problems when starting). 4" fan cost is $75 on ebay. Does anyone think this will work? By physics it ought to work but reality often interferes with pure physics ;-)

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  2. stee6043

    stee6043 Minister of Fire

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    I'm not sure 200CFM would be enough to really help in this application. Regardless of the inducer you find and use I think you'll find that the location of the smoke pipe in your upper chamber is problematic for "mid burn" reloads.

    I added the New Horizon draft inducer (now stock on the EKO's) and find that it does help eliminate 100% of the smoke during a normal reload (down to coals, or quite close) but it is still impossible to load mid-fire without significant smoke escaping. I very rarely load when it's not ready but when I do I have a 1000CFM 8" blower fan with an 8" flexible hose that I have vented outside for catching the escaping smoke. I also use it when cleaning out ash to keep the house 100% clean. That's the only 100% surefire solution I've found and it's not convenient if you're going to do it every time...
  3. Hunderliggur

    Hunderliggur Minister of Fire

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    I have that option also. A an outbuilding, I can add an exhaust fan like yours without much problem. Good to hear from experience what may or may not work.
  4. Singed Eyebrows

    Singed Eyebrows New Member

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    Thats what Froling did(small draft hood) when they could have had the computor speed up the draft fan. Short a $1200 draft fan on chimney top, the hood is probably the way to go, Randy
  5. pybyr

    pybyr Minister of Fire

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    Count me as one who thinks that the original concept of a venturi- type inducer might well work. It's the same concept that "jet pump" well pumps operate by.

    I found a commercial product that uses this exact principle, but, being for commercial applications, I'll bet it is not cheap:

    http://www.quickdraft.com/products/draft-inducer

    I've thought of trying the same thing but have not gotten around to it.

    I think you would want to use a "blast gate" of the type used for dust collector systems to block off the auxiliary blower during normal operation.

    If you try it, please let us know how it works
  6. Jesse-M

    Jesse-M Member

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    Here is mine........Anything close to what your thinking?........Works well for me, piece of exhaust pipe and a fan from one of those blow up water slides. Not sure of the CFM but its a bunch.

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  7. taxidermist

    taxidermist Minister of Fire

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    I messed around with this idea last year. No real good results so I installed a hood and a whole attic fan on my roof then piped down 8" to a range hood gutted out. No more smoke in my building.

    Rob

    ps nice barometric dampner.....I have seen a set up like that somewhere before. LOL
  8. Hunderliggur

    Hunderliggur Minister of Fire

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    Jesse - Almost exactly what I was thinking. And it gives me an idea - try the pipe (at most a loss of a flat 8" cap) with the exhaust from a vaccum. If it works, find an appropriate fan, it not, do the exhaust scheme.
  9. tom in maine

    tom in maine Minister of Fire

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    Dumont and Jetstream used a similar concept. It worked for them with a vertically fed fuel tube.

    I have not tried it, but it is on a list of things to try sometime. Please try it and save me some time :cheese:
  10. Duetech

    Duetech Minister of Fire

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    200cfm is probably not enough because it does not create the velocity needed to overcome the pressure in the combustion chamber. What you are trying to deal with is the increased pressure in the combustion chamber caused by the burning fuel getting the oxygen it needs by opening the door (and escaping throught the path of least resistance). My eko40 has an upper door about 17"x10" or 170 sq inches. If your smoke stack is 8" (mine is 6") your stack diameter is about 50 sq inches or over 3 times smaller than the open door. It's crude comparative math but if your 200cfm blower outlet is only 1/4 of the area of your exhaust pipe it's only about 1/12th of the area of your door. You don't need 2400cfm (a 1 for 1 comparison for your doors size) because you don't need the venturi to propel the exhaust gases at the speed the air is coming out of your 200cfm blower but it might not hurt to have a 900 to 1200 cfm blower with a variable speed. I don't have the math formulas you need but I know I am on the right track. For my eko40 I built a back draft damper plate that went across the door (and swung in during loading) to help force the pressure out the hole created by the open flapper valve. It worked good but needed to be of heavier construction than I made it. Any how with a back draft damper you could get by with a smaller blower for the venturi because the damper would be countering some of the pressure created by the open door.

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