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Distribution blower filter? Why not?

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by P38X2, Dec 1, 2012.

  1. allFIREDup

    allFIREDup Member

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    The filter is not completely fire proof though. as long as it doesn't come into contact with a flame it should be fine.

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  2. imacman

    imacman Guest

    I think this is the only way to get it done w/o any CFM reduction. Even the biggest mesh furnace filter material I used showed a pretty significant reduction in airflow.
  3. allFIREDup

    allFIREDup Member

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    the door is off my stove at the moment.....putting in a new gasket...can't test it out.
  4. allFIREDup

    allFIREDup Member

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    A little cfm reduction won't make a difference in my case. i've always run the blower on low and it heats my house easily. i'll just crank up the blower speed a bit if i have to.
  5. jtakeman

    jtakeman Minister of Fire

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    If you use something like this(see pic's) and flexible ducting to the inlet(adapter flange needed) on the conv blower. You gain surface area. But it might not be atractive with a living area stove. The box can hold a larger filter to increase flow.

    Capture.JPG Duct-Filter-Box.jpg
  6. Hdhogger

    Hdhogger Burning Hunk

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    If you add a filter or more duct to an exhaust or supply air system it will increase the static pressure. To overcome this you will need a more powerful blower to deliver the operating CFM that it was delivering before the added filter.
  7. allFIREDup

    allFIREDup Member

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    well i have a small electric heater with a piece of foam on the blower for air filtering, and when i remove the foam the cfm doesn't appear to change much. I can live with slight cfm reduction in order to keep the dust bunnies out.
  8. P38X2

    P38X2 Minister of Fire

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    Just took a quick blip to the hardware store. Couldn't find anything except those steel wool looking kitchen scrubbers. MUCH coarser than #4 (or whatever it is) steel wool. Unfortunately, they only had one in stock.

    I'm thinking make a cylindrical "box" with 1/2" chicken wire stuff on the bottom and magnetic tape to secure it. Place 6 or 8 scrubbers in there. When they get dirty, you'd probably only have to replace the top layer of pads and be good to go. Not sure if they'd reduce the flow but it may only be a trivial amount. They're very coarse...and non combustible :)

    ETA- Anyone know what the approx clearance is on the Harman blower? My back and neck aren't in the contorting mood at the moment.
  9. allFIREDup

    allFIREDup Member

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    the magnetic tape isn't strong enough to secure something like that.
  10. Harvey Schneider

    Harvey Schneider Minister of Fire

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    As long as your turbocharged blower doesn't pull more current than the control board can handle.
    Speaking of pulling more current; As the static pressure increases due to filters, ducts and such, the current drawn by the motor will increase (the motor is doing more work). The motor will run hotter and the control circuit will run hotter. Not necessarily a problem, just something to keep an eye on.
  11. Hdhogger

    Hdhogger Burning Hunk

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    You're absolutely correct. I've been in the ventilation business for 39 years and have seen it all.
  12. P38X2

    P38X2 Minister of Fire

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    You don't think so? Can't imagine the proposed contraption weighing more than a pound or so.
  13. allFIREDup

    allFIREDup Member

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    it wouldn't hold the contraption i made and my contraption weighs much less than a pound. i needed 4 small round extra pull magnets from a hobby store...they are the size of a watch battery.
  14. Hdhogger

    Hdhogger Burning Hunk

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    Harvey I have to correct myself here. Actually adding static pressure to a forwad curved blower wheel reduces the load on the motor. The wheel can't grab as much air so the motor isn't working as hard. The amp. draw and cfm will decrease.
    You will have motor overload when removing static pressure from a forward curved wheel blower system. My bad.
  15. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    You just need to have enough air supply that reaches the blower intake, lots and lots of smaller holes will allow that to happen.

    You have to be certain that there are still unplugged holes for air flow through the filter over a certain time span.

    Most stove shells have holes in them for this purpose.
  16. Hdhogger

    Hdhogger Burning Hunk

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    That's right Smokey, but if filters are added to the blower it will reduce CFM reducing the heat output. This might increase the total stove temperature. I don't know how this will affect stove. Anyone done it yet?
  17. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    You add the filter to the stove not the blower.

    The blowers intake is approximately 28.3 square inches on my 230 CFM blower.

    An appropriate filter size is going to be much larger than that and installed on the stove shell if one were to look up the effective air flow cross sectional area of the filter material one can size the filter to the air flow need plus slop to handle the build up.

    Say along the size of 20" x 15" or 300 square inches

    An even better setup would be an electrostatic filter system to pull the crud out of the air stream as this wouldn't block any air flow and only needs to be big enough to get that crud off to the sides.
  18. Hdhogger

    Hdhogger Burning Hunk

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    If the stove is designed for filters this is fine. My Cab50 was designed for free air delivery (non filtered). All air filters added to a system create static pressure which reduces CFM. To compensate, an increase of CFM is required to give the same air delivery.
    If filtering the stove shell the same terminology applies if the stove shell is air tight other than intake ports.
  19. Bioburner

    Bioburner Moderator Staff Member

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    My bixby has a 16 by 16 furnace filter.Was very good in keeping the house dust free. I know of a kit to remove fan from stove (Harman P). Will have to see if still available. I would like to put the fan in a filterable, sound absorbing box(wood with baffle or two). Any direct impediment of the fans inlet is not good. Had a short discusion with a good heating and cooling engineer about fans etc.
  20. mepellet

    mepellet Minister of Fire

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    I think the fan will likely run at the same amperage no matter what static pressure it sees. In some heating systems a static pressure sensor is placed to maintain a constant pressure. For example, if a filter gets dirty, the pressure drops in the system so the sensor could relay that and increase the amperage.
  21. Hdhogger

    Hdhogger Burning Hunk

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    Forward curved blower wheels are very sensitive to statice pressure. As a filter gets dirtier the static pressure increases, motor amperage drops because of a reduced air load on the blower wheel and motor. When a new filter is installed, the system is running with a maximum air load which increases motor amperage and air delivery.
    After 39 years :)oops:) of air system design and fan & blower sales believe me this is the way it works.
  22. jtakeman

    jtakeman Minister of Fire

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    Actually the amp draw goes down as the fiter gets dirty. There is less load on the impeller. So less load on the motor.
    heat seeker likes this.
  23. mepellet

    mepellet Minister of Fire

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    So the control boards are smart enough to see a load decrease and vary the convection blower amperage based on that alone?
  24. Hdhogger

    Hdhogger Burning Hunk

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    If the control boards do have the ability to control RPM to bring the motor up to run amperage that would be great. Then there would be no problems adding filter.
    mepellet likes this.
  25. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    No it is a function of what the blocked input to the blower does to the load on its motor, it decreases it and the motor just goes along for its normal spin around the block. .

    If you make the mistake of blocking the discharge the load on the motor increases and the current being drawn through the controller increases leading to problems for both the motor and the controller.
    heat seeker and jtakeman like this.

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