PVC vs Metal Duct

[Jim Barrett]

Hello,
I recently received my new Oneida Commercial D/C system and I am in the process of installing. In my other shop I used PVC and it worked fine for my application.
I received my duct system design from Oneida and they spec out primarily 6" duct. Expensive, plus Oneida charges a 25% re-stocking fee so I need to get it right the first time if I choose to use their ductwork. Right now I need to configure my system for a MM 300 Smart combo, MM 16 Bandsaw, workbench, floor sweep, and a 6x48 belt sander.
Looking for any input.
Thanks,
JimB

[Tyler Howell]

I think the task is overwhelming and you should ship all that stuff to me for proper assessment, safety checks and evaluation. :D

[Scott Coffelt]

Besides the old debate out there about running plastic for ducting vs. metal. I guess that's really up to the old self.

I myself, choose not to take a risk and used metal. I found 26 gauge spiral pipe in 10 foot sections at a local HVAC distributor. The pricing as much better then Onieda. I just didn't have the dollars to spend on their stuff. For fittings I used HVAC components, but would would recommend using either the econo versions from Penn State or Ken Craft. I made my 6" gates. Often the designs I have seen from the professionals has pipe reductions, I myself ran 6" to the tool if it could handle it or be modified. For those that couldn't, I ran 6" to the blast gate and then reduced to 4", trying to have the shortest run of 4".

Good luck.

[Steven Wilson]

The metal pipe isn't very expensive, but the fittings tend to be. By working and reworking your design I bet that you can reduce the expense for fittings. I'm in the process of hooking up my system to support a CU350, MM20, and various other tools. I chose to go with Oneida duct work with Nordfab fittings for the machine connections (Nordfab is pricey). I figure with 20K in equipment, and $1500 in a DC, spending $1K on pipe and fittings isn't too bad (5%).

[Jim Becker]

Congratulations on the new cyclone...I've very pleased with mine and suspect you will find yours "rocks", too.

Don't compromise on the design of your duct work, regardless of what material you end up using. Your 2hp Commercial Cyclone system requires a 7" main run out to at least the first branch for maximum performance. You have-ta use metal for that! As Scott indicated, you can shop around for the staight pipe and get good deals. But be sure to buy proper wyes...HVAC metal wyes are "backwards". You can also use metal for the 7" portion of the design and transition to PVC after that if you choose.

I'd suggest you stay at 6" all the way to the combo machine and only reduce at the hoods. You may need a 120mm adapter; my FS-350 did, but I don't know what they have on the CU300. I found that the 6" drop to the J/P really reaps benefits when jointing and planing wider lumber. A 4" hose will press fit over the 100mm connector on the MM16 no problem. Floor sweeps work great at 5" in my shop. (I have two)

[JayStPeter]

I've been having the same thoughts myself. Oneida did my design. Their recent price hike has made a difference in my thoughts of "it's only $x more to do metal over pvc".
Plus, I just paid off the credit card and drywallers for the shop. Ouch, can you say waaaay over budget :eek: . I think I'd rather have metal, but the checkbook is saying PVC with homemade blast gates.

Jay

[JayStPeter]

Stephen,
Wow, only $1K. I guess there are cost savings benefits to having a combination machine. Mine is up around $1500 for the cheap stuff.

Jim,
The Oneida designs I got for my 2HP commercial (with the monster filter) only went with 7" for the first 24". Then straight to 6" and to 5" for almost all the drops and even some of the longer runs. It's one of the things that sort of bothered me about the design after reading so much about keeping the pipe larger. I understand the concepts and physics of balancing CFM vs. flow velocity. But, I originally called to buy a 3HP system and they down sold me to the 2HP system. Now, they're saying there isn't enought oomph to drive the large pipe. The max run length is around 40' along the ceiling.
I guessing that the thing will work great no matter what I do.
I installed the door on my DC closet this weekend. I haven't yet vented the closet, or installed the knob. When I fired up the DC the door came flying open. Pretty good amount of pressure to hold the door shut.

Jay

[Jim Becker]

Jay, I have about 5 effective feet of 7" duct on mine and if I had known better, I might have brought it further out. I don't think that the system would have much problem with extending the 7" material longer, nor with keeping the backbone at 6" for a longer run. Drops are what they are...I happen to like 5" drops for most tools as the increased velocity isn't horrible for vertical runs and the hoods on the tools, themselves, don't benefit much from huge pipes...unless you can retrofit the machine with something bigger. Sometimes you can. Sometimes you can't. The 5" drop to my cabinet saw keeps the interior clear for the most part...and the port is still 4". The 2hp Commercial system really pulls air.

BTW, I have one section of 7" (5') and some 6" available if you or anyone needs it. The price will be good...:o

BTW-2, I probably have 40' from the cyclone to the drops at the end of the line. Incredible system. Even my miter station with the port underneath and small hose to the blade guard gets good extraction.

[Steven Wilson]

Jay,

I'm running (or soon will be when it arrives) about 4' of 7" pipe that then splits off to two 6" runs; one that goes about 10' and ends of with 3 5" gates, the other goes about 15' and then drops down to end with 2 5" gates, another split goes another 20' to the lathe (sanding hood) where it ends in a 5". Anyhow, the combo will have two 5" gates (a 6x5x5 wye). When used for the tablesaw I'll have 5" to the machine base and 4" to the saw guard. The guard will be terminated with a 60mm ID raw to 4" QF Nordfab reducer. Each of the 120mm ports on my CU350, plus the shaper hoods will be terminated with 120mm ID raw to 5" QF Nordfab reducers ($26 each - ouch !!) The end of each flex hose is fitted with Nordfab QF, I bought a couple of 5"QF to 4" QF reducers to handle transitions from 5" flex to 4" machine fittings. Each 4" machine port will have a 4" ID raw - 4" QF machine adapter. I plan on attaching the machine adapters (4"-4"QF, 60mm-4"QF, and 120mm-5"QF) permanently with duct mastic and rivets. The main piping will be fixed with sheetmetal screws and silicon so that It's removeable when I move. The connection to each machine will be with Nordfab QF fittings to make it easy to add sections of flex hose or to hook up machines when needed. Hopefully it will all work out, I should know within the next two weeks or so.

[Jim Becker]

The main piping will be fixed with sheetmetal screws and silicon so that It's removeable when I move.
I found that the heavy foil tape is more than sufficent in strength that you can eliminate any mechanical fasteners other than at particularly stressfull points, such at overhead drops. I used a few pop rivets there rather than screws that stick way into the air stream. Removing them is easy with a drill bit should you need to make changes or move. I only used mastic on the wyes to seal the leaky welds.

[Robert Ducharme]

I talked to a variety of people (will not mention their names to protect their reputations) some of which are not on the forum. There is a problem with the foil tape in that it can sometimes not hold as well as other tapes. :(

I did not use any sealant. I did use screws (figured the air flow was so fast it would wear off the tips after a week :D ). However, I did use a special tape for sealing the joints. This is over in the vent supplies near the foil tape in HD. I am trying to remember the number - something like 557 or 357. This tape is good to 180 degrees and is extremely sticky. A plumber acquaintance says that unlike duct tape, after it sets up you need a knife to remove it . Been very happy with using it so far (except I did have to remove a piece once and yes I did need a knife to cut if off).

I also replaced some foil tape I had on my IR pipe (intake/exhaust vent) with this material. Turns out as I removed the foil, I could see where water was leaking past it. The foil was barely sticking on the pipe.

[Jim Becker]

Robert, that's interesting what you write. In the occasions I've had to remove the foil tape for "system redesign"...I had to use a sharp knife to slit it and then spend a lot of time prying it off. It stays stuck solid...as long as the duct you are sticking it to is clean and dry when you stick it. At least this is my personal experience over several years. The only issues I've had with this stuff is if there is enough flex in a joint that it can crack the tape, that joint should also be reinforced with mechanical fasteners, such as pop rivets or screws. Maybe the tape I had was better quality (from an HVAC supply, not the 'borg)?

[Robert Ducharme]

Nope, good quality stuff. However, the tape was attached where the flex pipe joined the hard stuff. Since there is vibration there and some water comes down the pipes if the wind blows right that may have had an impact. By the way, the same foil tape in other parts also had to be cut off. Could also have been something related to the cleanliness of the pipes in those areas.

[Jim Becker]

However, the tape was attached where the flex pipe joined the hard stuff. This confuses me. You're not saying you used the tape to seal flex to duct are you? I don't thing that's an application that would work well. A good, sturdy compression band "cranked to eternity" will seal that connection off!

At any rate...I'll keep my eye on things to insure that I don't have any tape letting go over time. There sure is a lot of it in my system!

[Robert Ducharme]

Nope, the connection between flex and hard pipe is with a clamp. However, the hard stuff is a 90 degree elbow. These joints were sealed up - however, since they are "flexible" they did vibrate slightly. It is warm and fuzzy now. :)