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Thread: Underground ductwork?

  1. #1

    Underground ductwork?

    I'm planning an addition to my shop and will be redoing my dust collection system. I would like to run ductwork under the new concrete floor to go from my Oneida dust collector to the area where my table saw and jointer will be located in the center of the shop. Both of these tools have 4" ports) Question # 1: Is this a good idea? 2) Although my ductwork is metal, would a 6" pvc pipe be better to use underground? What type of connectors would I need to go from the 6" pvc to the metal ductwork above ground? (the oneida outlet is 7" and I do have a metal reducers) Thanks for any suggestions you may have.

  2. #2
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    A friend of mine put metal underground and his fills with water every spring. Long term that''s not going to be good for it either. Transitioning from PVC to metal is pretty easy using off the shelf HVAC reducers.


  3. #3
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    Use PVC under the floor, and glue the joints. Use whatever you want above floor level.

    Charley

  4. #4
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    I have no personal experience to add, but I remember Alain Vaillancourt puts his ductwork under the floor while building his new shop on YouTube. Check it out here. The episodes where he preps to pour the floor and where he hooks up his cyclone will probably be of most interest to you. But the whole build is great to watch.

  5. #5
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    A slightly different approach is to cast a trench in the concrete, and make a cover for it from wood or steel or whatever you like. You drop the DC duct into the trench, and put the cover on. There are several nice things about this approach. First, it is easy to modify what you have under the floor -- add a power line, add an air line, increase the duct diameter, etc. Second, you can get at the DC duct to repair it if need be. That's unlikely, but still...

  6. #6
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    A couple of times I've had to pull my DC piping apart to clear a jam. (not a great idea to suck up long curly shavings off the lathe, I guess) I'd hate to have to jackhammer the floor to do that. I'l love to have piping under the floor, but I'd definitely go with the trench approach.

  7. #7
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    I have always wondered if doing this would cause condensation in the duct, allowing sawdust to stick and build up, like in a dryer vent. Of course the dryer vent has warm, moist air in it to start with, but still...

    Does anyone who has this setup have a problem with this?
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  8. #8
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    You've heard the comment that something is set in stone. That is exactly what you will have if you put you DC piping under a concrete floor. Future modifications become a major under taking. Clearing clogs could also be difficult.

    A high water table or leaking pipe could fill your duct work with water and mold could potentially be an issue.
    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

  9. #9
    I see the advantages to having dust collection in the floor, but for me they are out weighed by the negatives rather quickly. Clogs being big, being able to change things the biggest for me. Not that either happens very often, but you're kinda hosed when they do.

  10. #10
    Last winter I did some reconfiguring my dust system, after purchasing a Hammer K3 Winner. I used short pieces of 2x4 to drop below the ceiling to hang the piping from, using that plastic plumbing strap. Imagine if the piping had been under the floor. Would make buying a new piece of equipment a major undertaking.

  11. #11
    As was said earlier - Trench it.
    Things change or need service over time.
    The issue with a trench is keeping it sealed or clean.
    Consider using steel angle embedded in the concrete and gaskets/ screws to keep it tight.
    If water could be an issue slope the bottom of the trench and put a well at end for a sump pump.

  12. #12
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    There are some real advantages to running DC and electrical under the floor as you propose. I would form a concrete "utility" trench and then have a removable cover, probably out of steel so you would have access should you require it. Just running ductwork in concrete doesn't leave you with any good options for cleaning out the inevitable clogs.

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