Custom reverse flow exhaust vent?

Discussion in 'Reverse Flow' started by jcweis1, Jul 11, 2014.

  1. jcweis1

    jcweis1 Fire Starter

    Would a rectangular duct with the same volume and cross section as a round duct - flow air the same? I was contemplating using a 24" x 2.5" x 20" rectangle duct in placement of a 8" x 24" duct


  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    NO...... calculate the surface area of the rectangular duct..... calculate the surface area of the round duct... FRICTION is the worst enemy of a natural draft system.....
  3. jcweis1

    jcweis1 Fire Starter

    Thanks... I thought it would not work.

    any ideas on different materials for a 8" duct? not a fan of the big box store duct work they have since they are flimsy. I know I can buy thin wall tubing but trying to find a cheaper way
  4. Do you any pictures of what you are building,?  I like round, check with your local welding and fab shops or the scrap yard

    Gary S
  5. radioguy

    radioguy Smoking Fanatic

    Take a look at your local scrap yard, lots a pipe cut offs. I used a 3.5" diameter post from a basketball hoop....10-11 ga. Welded up fine.

  6. jcweis1

    jcweis1 Fire Starter

    Yes I checked the two scrap yards around me here in CIncy but the only 8" pipe they had was real thick walled, just keep looking. Hate to pay for new tubing
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Exhaust pipe at a diesel truck shop...
  8. lngliv3

    lngliv3 Meat Mopper

    I was going to say big truck exhaust . They usually have in stock 4"5"6" pipe chrome , or aluminized pipe
  9. jcweis1

    jcweis1 Fire Starter

    Can two exhaust pipes be used?

    How would one calculate the diameter and length needed for two exhausts?

    How would one calculate the size of each plenum?

    One 8" would have been 23" according to the Feldon Calculator for my application -anything less in diameter would be too tall.

  10. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Use 2 each 6" exhaust the same height as 1 each 8" exhaust is called for in the calculator...
  11. jcweis1

    jcweis1 Fire Starter

    Thanks Dave.. two 6" it is. Any suggestions on opening size of a plenum? One plenum  per stack or one for both?  I have 24"- 26" width to work with.


  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Check the recent builds.... Someone just put 2 stacks at different heights.... one at the lower food grate and one at the upper food grate.... Ask that person how it worked for them.... New concept to me but... if it works to move the heat/smoke through the CC as I think it should, would be a good deal..... Also, you may need a choke plate on each stack to adjust and even out the exhaust flow....

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