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Thread: Dust Collector Duct Along Sloped Ceiling

  1. #1

    Dust Collector Duct Along Sloped Ceiling

    Have a Grizzly G0441 3 HP Dust Collector. Shop is 26' x 28'.
    Wondering if there are any issues, besides gravity, with running duct down the slope of the ceiling (approx. 13' would be 'sloped' at 2/12 pitch).

    Planning on running 7" main branch and breaking off 6" for machines.
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  2. #2
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    The dust doesn't care as it's being carried along by the air flow your DC generates. Gravity has very little effect for this particular kind of thing. What's more important is keeping your transitions in direction, etc., as smooth as possible.

    As an aside, I will not be in a sloped ceiling situation with my new shop, but the dust collection system I've opted to use is down near floor level (Harvey G700), so I'll be angling UP the wall to get to "distribution height" to workstation areas in the middle of the structure.
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    I agree with Jim. If the dust collector can move the dust from the machine port near the floor up to the ceiling it should not have any problems moving it up the gradual incline of the sloped ceiling.

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    I think I'd stick with the 8" ducts, personally. You might find 7" harder to find.

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    Quote Originally Posted by Andrew More View Post
    I think I'd stick with the 8" ducts, personally. You might find 7" harder to find.
    7" duct is readily available in snap loc, spiral and quick connect metal ducting. It's just not available in PVC/ABS.
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    Quote Originally Posted by Jim Becker View Post
    The dust doesn't care as it's being carried along by the air flow your DC generates. Gravity has very little effect for this particular kind of thing. What's more important is keeping your transitions in direction, etc., as smooth as possible.

    As an aside, I will not be in a sloped ceiling situation with my new shop, but the dust collection system I've opted to use is down near floor level (Harvey G700), so I'll be angling UP the wall to get to "distribution height" to workstation areas in the middle of the structure.
    In my shop one branch was kept at 36" height ( its a long story ) , but it is my best from a CFM perspective . I got creative with using the wall space that remained , and probably won't ever change that area . With the new Harvey collectors if you don't need to go up-then back down , more options are possible , but somewhat hard to accept . It can be scary .

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    I unfortunately do need to "go up"" for the new shop building once it's up because much of the machinery is in the "middle", as it were. But I will be able to go up at an angle after a short straight run to the inlet which is the least distance. I'm not worried about gravity at all with the system and am designing things to keep the dust work as "short" and direct as possible. It's given me a chance to really think about workflow, too.
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    Quote Originally Posted by Jim Becker View Post
    7" duct is readily available in snap loc, spiral and quick connect metal ducting. It's just not available in PVC/ABS.
    Define "available". Most places will have a 7" straight piece, but when you're really frustrated and working late, it's nice to be able to go to the big box store and just grab a fitting. You're more likely to find an 8" Wye or elbow or conversion or 8" to a register boot than 7".

  9. #9
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    Yes, that's true for the big box stores, Andrew. But HVAC wyes are backwards for DC and require reworking plus box stores rarely have the heavier gage components that are best for dust collection systems, anyway. My comment around readily available was relative to suppliers of dust collection components. I'm sorry I wasn't clear about the source I was referencing.
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    Quote Originally Posted by Jim Becker View Post
    Yes, that's true for the big box stores, Andrew. But HVAC wyes are backwards for DC and require reworking plus box stores rarely have the heavier gage components that are best for dust collection systems, anyway.
    I know I'm working with a lowly 1 1/2 HP Grizzly, but I've yet to come across any references to a 26 guage duct being crushed by a DC, even some of the nicer 5 HP models. Maybe it happens, idk, I just don't see it with the static pressure most DC are capable of generating. So usually just HVAC stuff is fine for even the pro-sumer level stuff. The wyes I get from my local HVAC supplier aren't necessarily backwards, they can be crimped either way, but even if they were, it largely doesn't matter that much, since it's often the shrouds that need the actual attention, not a little bit of saw dust caught in a crack, and a minor bit turbulence.

  11. #11
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    26 gage is actually what you want. But it's not always available at the home centers. My local HD sometimes has a few pieces; the local Lowes doesn't carry it at all. Typical HVAC duct work is closer to 30 gage which works for that application because the static pressure is very low and presents very little "vacuum". Dust collection is a different story. Even though dust extraction from larger tools relies primarily on CFM...air flow...restrictions in flow can raise the static pressure enough that larger systems can collapse thinner duct work.

    One thing to check on the elbows, wyes and other components you acquire from the home centers is to be sure you seal all the "joinery" on the components with duct sealant or foil tape. The quality of the welds, if they exist, and/or rivets seems to be dubious on a lot of stuff offered today. Stuff from an actual HVAC supplier may be better quality. Running foil tape down the snap-lock joint on the straight pipe is also a good idea, IMHO.

    I do understand the fun with this type of metal duct work as the collection network in the shop at our old property was all snap-lock. While all the original components came from Oneida, changes and additions over time often were performed with stuff acquired from Home Depot. I'm sure I made the foil tape manufacturer very happy with the revenue increase.
    Last edited by Jim Becker; 07-09-2022 at 10:58 AM.
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    Quote Originally Posted by Jim Becker View Post
    One thing to check on the elbows, wyes and other components you acquire from the home centers is to be sure you seal all the "joinery" on the components with duct sealant or foil tape.
    Yes this is good advice. I'm partial to mastic personally, it seems to do a very good job, and I can usually "borrow" some from a buddy of mine who does HVAC work. Otherwise it gets a bit pricey to buy another $20 bucket when you just want to butter a few new joints.

  13. #13
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    Yea, the mastic works beautifully, but if one has to buy a large quantity, foil tape is a lot more economical. The tape also eliminates the needs for pop rivets in most locations...only the ones that actually see stress need to be "popped".
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