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Thread: Dust exhaust size? Through the shop wall?

  1. #1

    Dust exhaust size? Through the shop wall?

    I'm just about ready to break ground on a new shop. I'm planning on a two-stage HF DC system that will be ported outside. The wall that it needs to go through will be concrete ICF (styrofoam blocks). I was planning on running 5" PVC through the wall since the HF DC's exhaust port is 5"... but I'm struggling to find 5" pipe. (And I need to put this exhaust pipe through the forms before I pour the concrete.)

    For that short run through the wall, how big a deal would it be to bump it down to 4"?

    Thanks in advance.

    T

  2. #2
    I wouldn't restrict it.

    I would go with 6" and use a 5x6 adapter.

  3. #3
    Join Date
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    I would bump it up if anything. Make it a large rectangle. That way you can build a manifold for current DC (and your next DC without having to break out the hammer drill). Your exit should be at least the area that the machine has designed into it.
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  4. #4
    Makes sense. I'll see what I can dredge up.

    T

  5. #5
    The rectangle is a good idea. I could surely build that out of pressure treated lumber.

    T

  6. #6
    Anyone know the dimensions on the HF outlet -before the 5" round transition?

    T

  7. #7
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    I agree with the advise to bump up the size of the hole through the wall...you may replace that small DC setup with something larger in the future and given your construction type, it's easier to perforate the wall larger now rather than retrofit later, regardless of what size duct you send through it in the near term
    --

    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
    If I remember correctly the rule of thumb should be 3 times the area of the outlet on the DC. So the 5" area is about 20 sq in x 3 = 60 sq in. That is about an 8 1/2" diameter pipe or 6"x10" rectangular. So knocking out 1 block allows you to upgrade down the road. The above applies if there is some distance between the DC and the wall. If right beside each other then you could blow straight out with the same pipe but any louvers or hoods on the outlet will restrict the air so you might as well go with the 3 times opening.

  9. #9
    Where are you located, Tony? If you will be trying to heat your shop in the wintertime or cool your shop in the summer, the movement of air from inside your shop to the outside could affect your overall energy costs. This could be something to keep in mind in your planning.

  10. #10
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    I would go with 8" pipe for your concrete pour and then run your 5" duct through it.
    Lee Schierer
    USNA '71
    Go Navy!

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute

  11. #11
    Think of whatever you are going to pour into the concrete wall as a sleeve. It's there so you don't have to core through concrete later. Lee's suggestion to install an 8" sleeve is a good one and will allow for later expansion and give you the option to use the sleeve for other purposes such as running power or air lines through it.
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  12. #12
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    Make sure you include an adequate return air. Remember, the return air won't have the motor driven fan of the DC system helping move air through it so it (return air) needs to be larger opening. Otherwise you will have such large negative pressure in you shop that air will be pulled through places you may not want it coming through such as combustion furnace or wood stove flue (not healthy), and through openings around windows, doors, etc.

    You can install a pressure sensitive switch in the DC system that will open a damper in the return air when the DC system turns on. I don't know where you live but if in a mild climate you may decide to leave the return air open or use a manual shutter or similar system rather than automatic. Best to get help with the return air sizing because if you size same or not much bigger than the DC outlet, it won't work unless you also install a fan assist on it. I suppose the fan could be a little smaller capacity than the DC system's fan if the return air duct is same size as the DC exhaust system. Also, negative pressure in shop will reduce efficiency of DC system.

    If you live where building codes are enforced, the inspector will make sure you have return air. Also, if you live in an area that looks after energy efficiency and the shop is heated, the inspector may require heat recovery on the exhaust/recover system.

  13. #13
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    Maybe code doesn't require return air for shops. If you elect to not use return air then you can open a window or door when you are using the DC system to avoid negative pressure in the shop. Return air would be more convenient than opening and closing window or door, especially if you are in a cold climate area. You could also use spring loaded hinges on a door and leave it ajar so that when the DC system turns on it sucks the door open. That is what I do when I operate my kitchen exhaust even though I have return air. My return air is same size as exhaust (10") and is not enough even at low settings. A heating contractor told me it wouldn't be large enough but I did it anyway. He was correct.

  14. #14
    Thanks for the chatter on the return air. Certainly something I need to dial in and hadn't considered.

    I'm in the middle of Idaho so we do have winter –but I'm going with electric heat and not wood or propane so at least I won't be back drafting smoke or CO.

    I should probably chat with my contractor about this issue and the building code.

    T

  15. #15
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    For the sleeve a old paint can or bucket may be cheaper then buying a short piece of pipe. For me it is cheaper to buy one coupling rather then a full stick of 8" pipe that I have no other use for.
    Bill D.

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