Dust collection through the floor

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Forum topic by Kelly posted 02-11-2014 02:17 AM 2804 views 0 times favorited 10 replies Add to Favorites Watch
View Kelly's profile


73 posts in 2859 days

02-11-2014 02:17 AM

Topic tags/keywords: dust collection ducts blast gates

Hi, I’m getting ready to install a dust collection system in my 16’x30’ shop. I’m considering a 3hp cyclone ( and am getting ready to layout my duct work. I’m not a big fan of having all the duct work on the walls and ceiling so I am considering building a sub-floor over the concrete slab and putting my ducts between the joists. I will make the ducts accessible by creating a chase in the floor where I can lift out the plywood should I need to get to the ductwork. My question is – what kind of problems might I encounter with this type of layout? My big concern is drawing the dust from the floor to the top of the cyclone which is about 6’ off the floor.

This is my first dc system and I have read several articles but any advice would be appreciated. IE blast gates, pvc vs. metal ducts…

PS. A second reason for the floor would be so that I can run all my electrical in a separate chase, thus eliminating ugly conduit on the walls. Any thoughts here would be appreciated too!

10 replies so far

View cooksmtn's profile


15 posts in 2620 days

#1 posted 02-11-2014 02:45 AM

Dusty, I have my ductwork under the floor. I have a relatively accessible crawlspace, so I wasn’t to concerned with having to get to a clog if necessary.

I started with a 1 1/2 hp wall mounted unit and 4” duct, less than 20’ total. Risers at the jointer and table saw. The blower was about 3’ above the floor, and routed through a trash can separator. A woefully inadequate system, but I never had a problem with the unit moving anything that it could pick up at the machines.

I recently updated to a 3hp blower on an Oneida cyclone, with the inlet about 9’ above floor level. A short run of 7” pipe to exhaust outside. Inlet is 6” until I necked down to the 4” at floor level (waiting on 6” fittings to re do the under floor, and extend farther for additional intakes).

Everything I researched indicated that velocity is the key to keep everything moving, even on the vertical runs. The unit, as it is now, really sucks (good!!).

I did all the calculations for velocity, pipe size, and cfm. Total pipe run will be less than 30’ to the inlet farthest from the cyclone, but I don’t know off the top of my head what equivalent run is when factoring in ells.

I also was anal about taping everything with foil tape (I used HVAC snap lock). Especially on the initial system, since I knew it was no better than marginal.

The few times I serviced the jointer and had that pipe open (downstream from the table saw), I couldn’t see anything laying in the bottom of the pipe. I will be dismantling as soon as my new 6’ fittings come in and am certainly curious about how much debris I will find in the pipe..

I have high ceilings, and have really appreciated being able to handle boards up to 14’ without hitting crap above me, which is one of the reasons I went with under the floor. And under the floor was shorter runs.

A chase for electric is a great idea. I will be running under floor circuits when I’m in the crawl space to my work island to eliminate 3 cords across the floor.

Bottom line: Even with my crappy first set up, I never had to go into the crawlspace to deal with the duct. I say, do your calculations, and go for it.

View Manitario's profile


2818 posts in 3934 days

#2 posted 02-11-2014 02:50 AM

I’m just in the finishing stages of a new 25×40 shop and I too considered putting all the DC ducting under a subfloor. I was building a subfloor anyways (wood is a lot nicer than concrete to work on!). I ended up putting the duct on the ceiling though for a couple of reasons:
-having the duct accessible gives me a bit of flexibility if I want to change my machine configuration or later add duct ports
-the less bends in a dc system the better; the most efficient systems have relatively straight runs. As well, there should be several feet of straight duct before the DC inlet before you have a bend. Putting the ducting in the floor, for me, would result in a lot of bends in the ducting system which I wanted to avoid.

-- Sometimes the creative process requires foul language. -- Charles Neil

View crank49's profile


4032 posts in 4022 days

#3 posted 02-11-2014 03:18 AM

You have to get the dust up to that cyclone inlet anyway. Doesn’t matter whether you go up at the tool then across the ceiling or wall, or if you go across the floor then up to the cyclone. The overall amount of lift is the same.

Also, “lift” as it refers to raising dust in an air stream is not the same as lift as in head pressure in a water pumping system. The only thing you have to be concerned with in a dust handling system is conveying velocity. If your air flow drops below about 2500 FPM you can bank on having heavy particle drop out and clogging.

That velocity is determined by the amount of pressure available and the diameter of the pipe. If you are sucking the dust through a machine fitting of 4” and if your collector is pressure starved then you might drop to that low velocity in a 6” pipe. You would have to either open up some bleed air or enlarge the machine’s connection port , or alternately just run 4” all the way if it’s not too long of a run.

View Jim Finn's profile

Jim Finn

2877 posts in 3973 days

#4 posted 02-11-2014 03:23 AM

I have a 22×13 foot workshop and I set up all my equipment so that I could run all the dust collection duct along the floor at the wall. It is out of the way and is still exposed. I ran six inch metal duct. (Snap lock). Works for me. Just another option.

-- No PHD just a DD214 Lubbock Texas

View Fred Hargis's profile

Fred Hargis

6919 posts in 3544 days

#5 posted 02-11-2014 12:16 PM

If you can access it easily, I don’t see a downside to under floor ducting. The possible exception might be making changes to the layout (that WILL happen). But again, if you have access, t shouldn’t be a problem. I know the concern of a clog, but truthfully after living with various forms of a DC for over 15 years, I’ve not had a clog in the pipes….though I have had a few at the ports on machines.

-- Our village hasn't lost it's idiot, he was elected to congress.

View shipwright's profile


8703 posts in 3849 days

#6 posted 02-11-2014 03:30 PM

Here is a blog link to my under floor system, lots of pictures. I have an 8” PVC vertical pipe from under the floor to a good six feet above the floor and another foot or so of elbow to join to the top of my DC. (Probably 8 vertical feet overall) It works really well.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View Kelly's profile


73 posts in 2859 days

#7 posted 02-12-2014 01:13 AM

Thanks for your advice/suggestions!

I thought I’d pass along a link incase anyone else, putting a dc together, should stumble on this discussion.
Bill Pentz has a great site with a lot of information and advice on what/what not to do when building a dc.

Thanks again!

View changeoffocus's profile


467 posts in 2668 days

#8 posted 02-12-2014 02:15 AM

Amen to Bill Pentz’s site, I’ve found It to be a single source of all things DC etc.

View Kelly's profile


73 posts in 2859 days

#9 posted 04-10-2014 11:10 AM

Yet another link, in case anyone working on dc sys. stumbles onto this page. Here is a great way, from ‘The Wood Nerd,’ to build cheep pvc wye’s –

This site also has several other postings about putting together a dc system which have been very helpful, so be sure to view all his articles/blog postings…

Good luck

View Fred Hargis's profile

Fred Hargis

6919 posts in 3544 days

#10 posted 04-10-2014 11:35 AM

I think my biggest objection to floor systems is changing them (you will have to change it at some time). But with access it sounds like you have that covered, so there’s no downside, and you do have it out of the way. As for type of pipe you can start endless arguments suggesting one material over the other. Both have been used successfully so I suggest you consider cost and availability. PVC is pretty much either 4” or 6”, and the 6” thinwall can be hard to find. Metal is in just about all sizes, but getting wyes instead of tees is a problem and if you go with snaplock there’s more work to seal the ducting. But you may find most of the cost in the fitting, so try to estimate what you want/need and start there….choose on what you can get, they both work fine.

-- Our village hasn't lost it's idiot, he was elected to congress.

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