Under Floor Dust Collection

[Jon Snider]

My new shop will have a wood floor with probably joists over a small crawl space. Not something I’d ever want to go down into to fix ducting. I’m thinking I’ll lay OSB with screws so they can be removed if I need to get to them from above.

So, having read most of Bill Pentz’ site and gone through the last 250 or so pages here at SMC, I’m at a crossroads. There are literally hundreds of dust collection posts, far outnumbering any other category, but there doesn’t seem to be much consistency. Pentz pretty much says put your ducts overhead. Otherwise, expect clogs or bulky material damaging the impeller. Not to mention possible fire hazard from high amounts of residual material in ducts. That option isn’t my best for several design reasons. Plus, in building a clear span structure w no internal posts, there’s no way I’m going to go anywhere but below to my central saw and jointer cluster.

Whats the real world experience, assuming good duct layout with a powerful motor such as a 5hp ClearVu and 6” ducts as close as possible to each tool?

One of my main concerns is the rise from the subfloor up to my DC intake.

Have others seen these problems? If I have a clog I can probably get to it to fix it but not interested in anything more serious.

Thanks much for any advice.

Jon

[Jim Becker]

Outside of unusual circumstances...excellent air flow and proper duct design cures all. Dust collection is about moving air. The air, in turn, moves the material. If you make that air move as efficiently as possible and with a volume (measured in Cubic Feet Per Minute - SFM) that exceeds the requirements of the tool collection expectation, etc., you should be fine regardless if your duct work is overhead or down below.

[Jaromir Svoboda]

Never had clog in 7 years. I just finished building my new shop and I put duct in floor again.

[Jon Snider]

Never had clog in 7 years. I just finished building my new shop and I put duct in floor again.

Jaromir. 6” ducts?

[Chris Parks]

The short answer is it depends, if the dust extractor cannot transport the debris it will clog so don't buy a cheap DE and design the system so it can be got at if necessary.

[Tom Bender]

A couple of pointers;

Install quick disconnects at places you may need to access.

Sometimes vertical sections are designed smaller then the main run so stuff will be lifted by the velocity. As Jim says, "proper duct design"

[Joe Jensen]

I have overhead ducts in my current shop. I do get small cut offs that get sucked up above the blade guard but the don't get all the way up to the horizontal so when the collector shuts off they fall down. I suppose you might get small pieces of scrap falling down into the ducts and then fail to go vertical back out of the floor, I never considered that. I am sure that disconnecting duct under the floor would be a major pain in the butt.

[Andrew Seemann]

Probably the biggest advantage of having overhead/above ground ducts is that they can be moved.

I've had 3 different shops, and all 3 times I have installed dust collection, I have ended up not liking the initial result, despite weeks/months of planning. Same thing with the machines, I always seem to find a better layout after I get everything in there. I can't imagine being locked into a specific layout by underfloor ducts. I have 9' 8" ceilings with a 6" main and flex duct coming down from the ceiling. No problems with clogs or lack of pull with a 3HP Oneida.

Granted a crawl space is a little more flexible than burying them in concrete. I'd say go for regular plywood rather than OSB. It will probably wear better. Also look for screws that can have the gunk cleaned out of the heads easily.

[Chris Parks]

I think my DE ducting is on the fifth iteration at least.

[Jon Snider]

Probably the biggest advantage of having overhead/above ground ducts is that they can be moved.

I've had 3 different shops, and all 3 times I have installed dust collection, I have ended up not liking the initial result, despite weeks/months of planning. Same thing with the machines, I always seem to find a better layout after I get everything in there. I can't imagine being locked into a specific layout by underfloor ducts. I have 9' 8" ceilings with a 6" main and flex duct coming down from the ceiling. No problems with clogs or lack of pull with a 3HP Oneida.

Granted a crawl space is a little more flexible than burying them in concrete. I'd say go for regular plywood rather than OSB. It will probably wear better. Also look for screws that can have the gunk cleaned out of the heads easily.

Thanks for your reply. Very helpful info!

[sean meltvedt]

6” pvc duct under concrete and steel. ClearVue 1800 sucking on it. No problems so far (3 years). Only issue is the permanence. So the entire run is not underfloor to each machine. Instead, I put them up along the far wall, and localized clusters of machines, and run along the walls for distribution. Not the best layout, but beats having it hang below the finished ceiling level above.
This partial underfloor has accommodated me rearranging the shop a couple of times.
So, yes if I were building again, I would run underfloor to key areas and above floor to the machine.
Good luck, and enjoy
Sean

[Bill Dufour]

Unless it is a deep trench the up turns will not be long smooth arcs so they will reduce flow.
Bill D

[Chris Parks]

There has been flow testing done in Australia that shows long curves flow worse than short curves contrary to what we all believed and to what seems logical.

[Jon Snider]

Mine will be in a crawl space under joists so plenty of room for long radii.

[Peter Christensen]

There has been flow testing done in Australia that shows long curves flow worse than short curves contrary to what we all believed and to what seems logical.

Chris would you pm me the link if you can find it? I know two forty-five degree corners are worse than a large radius ninety but had seen nothing about a long sweep being worse than a short one. Thanks