Metal or plastic?

[Wade Lippman]

I have done a search than read several threads on this subject; PVC or 26 gauge steel.
I have a 3hp Grizzly Cyclone, 13x25 shop, and will be putting 4 tools on it now; perhaps 6 later on.
My intent is to run all 6" to the machines, then drop down 4" to connect to the machine.

I can buy steel for $2.10 a foot and PVC for $1.50 a foot. I haven't priced fittings, but assume they are comparable. (If I am wrong; let me know!)

As I see it, steel has the advantage of not building up static electricity. As I understand it, SE can't make anything explode, but can give some nasty shocks. In my old shop I used 20' of 5" PVC flex and never got a shock off it.

PVC is cheaper, easier to work with, easier to modify; but builds up SE.

Is all this about right? If so, then PVC seems to be the clear choice.

Still, I am going to run a survey to see what you guys think.

[Rod Sheridan]

Hi Wade, I can't imagine anything being easier to work with then metal ducting.

I have metal ducting and don't use plastic due to the static shock factor.

Nothing gets your attention like bending down to pick up a piece from the planer and getting a static discharge to your head......After 2 or 3 experiences I went with aluminum flex...............Regards, Rod.

[Paul Wunder]

PVC.

Easy to install

Tight installation (no leaks) without taping, calking.

Less risk of cutting one's self

Readily available fittings

Less internal friction than most metal. Improves air flow

Easy modifications as needed

NO STATIC! What a red herring argument

[Larry Browning]

To me PVC is far easier to work with. It is easy to cut and fit. Also you don't need to glue the joints either, so dis-assembly is easy as well. However the PVC fittings may actually be more expensive than the metal ones. My personal experience tells me that the static elec thing is WAY over stated. I have had my system for 5-6 years now and have yet to experience my 1st SE shock from the system. So, my vote goes to PVC.

[Rick Moyer]

Three years and have never had a static issue with mine either.

[Alan Melbourne]

mine is metal but plastic is ok too. you will have to cut the metal with a mini grinder etc but thats not too bad.
i went for the metal because i started working out the cost and there was very little in it.

i would be carfull going from 6" down to 4".
mine ducts are 6" and i tried reducing down to 4" but it restricted everything too much.
i filled all the 6" duct all the way around with planer shavings. i changed the 4" to a 6" and put a 6" y with a 4"reducer on both sides of the y. the extra air coming in as soon as posible allows the full 6" to pull all the air .
i put a blast gate on the open side of the y . if i close that the pipe starts filling up straight away.

[Bas Pluim]

One thing to keep in mind is that the hose from the blast gate to the machine will be plastic, no matter what material you use for your duct work. That's the most likely area for you to zap yourself (if at all).

[Steve Milito]

To me PVC is far easier to work with. It is easy to cut and fit. Also you don't need to glue the joints either, so dis-assembly is easy as well. However the PVC fittings may actually be more expensive than the metal ones. My personal experience tells me that the static elec thing is WAY over stated. I have had my system for 5-6 years now and have yet to experience my 1st SE shock from the system. So, my vote goes to PVC.
Did you do something to try and have a ground conductor with the pvc or is it au naturale?

[Ole Anderson]

Steel here. Easy to install. Check BORG pricing on 26 gauge snap lock, should be about the same as you are getting for PCV, $1.50 per foot. Also available easily in one inch increments. Best if you go with a 7" main and 5" drops to your 4" hoses. Try that with PVC. Ever seen a professional install with PVC? Moving pipes? Just cut the tape, drill the rivets and away you go. Try ungluing or uncaulking PVC. 6" PVC is OK if you are running a 5 hp collector, not so much with a 2 or 3 hp unless you have short runs.

[David Kumm]

The choice is really only valid for 3 hp 14" systems or less. While it may create less resistance than equal sized steel, the lack of 1.5 ot 2.5 radius fittings takes that advantage away. If your system is larger steel optimizes it better. Dave

[Rod Sheridan]

One thing to keep in mind is that the hose from the blast gate to the machine will be plastic, no matter what material you use for your duct work. That's the most likely area for you to zap yourself (if at all).\

Exactly, that's why I indicated that I replaced it with aluminum flex..........Rod.

[glenn bradley]

It used to be that price was a driving force. PVC prices are nearly double since I put mine in 3 years ago. PVC still has the advantage of ease of working/changing/modifying but, that is subjective. All my hose has a wire helix. I hadn't seen hose in those sizes that were all plastic(?). In the winter we get some dry weather and something moving through the duct in those conditions will develop a charge. All that is required to never experience a static shock is to make sure that something is an easier path to ground than you are.

[Andy Fox]

6" PVC is OK if you are running a 5 hp collector, not so much with a 2 or 3 hp unless you have short runs.
Why is that?

[Robert Payne]

I'm another PVC proponent and have found that either silver HVAC tape or a length of stranded wire wrapped helically around the duct will pick up the static charge; add jumpers around blast gates and connect crimp connectors on the wire coil ends of flex duct to get any charge they carry and then route one or more locations to ground to dissipate the static without ever getting zapped. Even though PVC is a non-conductor, a fairly substantial static charge will build up from the moving particulates inside the pipe, but this bleeds it off before your get a jolt. The other advantage of price, internal smoothness, tight joints and easy modification all add to the advantage side. I've used PVC for nearly 20 years (first 4" and later 6" when I upgraded my DC). My blast gates are all ClearVue and they fit PVC perfectly. Just my .02

[Larry Browning]

Did you do something to try and have a ground conductor with the pvc or is it au naturale?

Nope, no grounding conductor. I think maybe one time I felt the hair on my arm raise a bit when I was close to one of the ducts, but it has never shocked me.

[robert morrison]

One advantage of steel over PVC is the 90* adjustable elbows that are cheap and handy. Two can make a nice sweep 90, or you can make whatever angle you want. With pvc you are limited to set angles of 90, 45, etc.

Lashing straps (where the strap runs thru a spring loaded clamp) are handy to temporaily hold up piping to permenatly secure.

Blast gates larger than 4" in diameter can be expensive. Homemade gates can be made with scrap for almost no cost.

[Lornie McCullough]

PVC for me.... no grounding, and I have never had a static shock from it. Years ago, I would get static shock from a 'shop-vac', but I no longer have one in the shop (I HATE that shock!!) . I have said this elsewhere, but: I don't glue my PVC, and I don't use any hangers to hold it up. The horizontal runs lay on the shop rafters, and the vertical runs reach to the floor for support, with y adaptors at whatever height needed for take off to each machine.

It is no effort at all to add to or move components .....

Lornie

ps spent time in the shop today making homemade blast gates to replace the metal prefab gates.

[Ole Anderson]

Why is that? ( 6" PVC is OK if you are running a 5 hp collector, not so much with a 2 or 3 hp unless you have short runs.)

If you run your ducting layout to your farthest big machine in a static pressure calculator like the one on Bill Pentz's site, you will see a lot of losses in your 6" pipe, and if you sub 7" pipe those losses will be cut substantially. You need a bigger collector (bigger impeller and resultant horsepower) to make up for the difference. If your main run of 6" is not too long, those losses won't be a big issue, but with longer pipes and more fittings they start to chew up your available static pressure at 800-1000 cfm, the range you want to be running for a TS with top and bottom collection or anything running a 6" final connection. For example if you have a main run with two 90 degree bends, a wye and 30 feet of pipe, and you are pulling 1000 cfm, your target velocity with a 6" pipe will be 5093 fpm and your losses for just that section of piping will be 4.86" wc (water column). Bump your pipe to a 7" and your target velocity at 1000 cfm drops to 3742 fpm and the losses drop by a huge amount to only 1.25" wc. When using Bill's spreadsheet be sure to input your cfm and the target velocity which is the calculated velocity in your chosen pipe size at the 1000 cfm. If you leave the target velocity at 4000 your answer will be wrong. The one major reason I am able to get good results in my system running just a 2 hp Super Dust Gorilla is that I have a 7" main, which by no coincidence, is the size of the cyclone inlet. So I am guessing that the guys running copious amounts of 6" PVC successfully are likely running a CV or other machine with a 15" impeller and close to 5 hp.

By the way, static discharge issues are largely dependent on relative humidity. If you live in the south where the RH probably doesn't go below 40%, static isn't the problem compared to doing woodworking in your basement in the winter in Michigan when the indoor RH is 20% or less. It seems the humidity in the air tends to drain off the static charge as it occurs. I would think that those living in desert climates also notice the static issues more.

[ian maybury]

Have not used plastic, but went for galvanised steel spiral on the basis that (a) it seemed plastic could result in problems with some know it all insurance assessor in the event of, (b) steel (direct from a HVAC fab/ducting manufacturing place) is much cheaper here, (c) it opened up the option to go to 160mm ducting (not sure if this is US option), and (d) there seemed to be more fittings available. The stuff anyway solders up easily to make odds and ends. e.g. stuff like machine connections.

The downside with metal is that it produces lots of metal chips if you cut it with a jigsaw (a fine HSS Bosch metal cutting blade works well), and the resulting edges are pretty hard on the hands - and of course the joints need sealing with foil tape. Some of the very light (thin wall) gauges are risk collapse with a powerful dust system it seems, I can't remember what the required minimum is. The fancy clip together Nordfab pattern stuff seems to be much more easily re-usable, and significantly less labour intensive to install - but at a significant price premium.

It sounds like it matters which exact type/schedule (?) of plastic you get (cost), and some can be hard to assemble (tight) and more expensive - but realistically there's respectable looking technical writings about that says the fire risk with plastic if any is minimal.

So its probably a pays your money takes your pick sort of deal...

ian

[David Kumm]

I agree with Ole's post although I go farther in not wanting the 6" mains on a 5 hp 15+" impeller system either. The impeller will pull more cfm at higher Static Pressure but it is still like buying a Corvette and putting a restriction filter and exhaust on it. Using larger mains allows more cfm to be pulled through the relatively small machine ports and increases the dust captured at the machine which is what it is all about. That pushes me to steel. Dave

[Jim Andrew]

8 years ago, would have used pvc but could only find the heavy 6" plastic. Now the thin wall seems to be more available, although they are not using it for sewers any longer. Went with the metal, and have gotten along fine, and have made several changes. My system is all 6" and my cyclone is 2 hp. Although I could probably use more hp on my sander.

[Steve Rozmiarek]

I use steel because I needed bigger than 6" pipe, and I like the sweep type elbows and fittings that are only possible with steel. Onieda spec'd my system to start with 8", and step down from there. Try finding, 8" or 7" pvc at your local borg. The longer radius elbows and transitions of steel are completely different than the abrupt transitions of pvc too. In my mind, the smoother transitions provided higher flow because of less restrictions.

[Gordon Eyre]

I hate SE so went with metal and never looked back.

[Michael W. Clark]

I have 4" PVC on a small system (small HP, short runs) and am planning an upgrade to get more CFM and better hooding. I'm going with metal primarily for the flexibility in sizes. For example, I want a 5" on my TS cabinet and to connect to a 3" shark guard for the blade, both of these brought back to a 6" duct. I haven't seen 5" in PVC and I don't like the thought of running 6" all the way to the cabinet port and reducing down. I don't have enough flow to support a 6" and 3" connected together.

I do prefer metal because it is conductive. The only shocks I have had are from the hose when connected to the planer (heavy dust loading in a dry basement shop). I have copper wrapped around the PVC runs to help dissipate any static but they still "grow hair" with dust that is laying around. If the dust is sticking to the outside, there is "potential" for it to stick to the inside, partially buildup, add restriction, and reduce flow. Not saying this is absolutely going to happen with every system, some situations may be more prone to it. For example, if you have your 15" planer located at the far end of the shop (30-40 feet away plus fittings) and marginal HP/impeller system, this situation may be more vulnerable.

[Steve Rozmiarek]

Doesn't it make sense that those of us living in very dry climates will experience more plastic induced static issues? I know my old Ridgid shop vac used to zap me pretty often, but less so in the spring when it is wetter. FYI, western Nebraska is VERY dry most of the time.

[Alan Lightstone]

I went with the metal Nordfab. Very pricey, but very nice. Need to figure out what fittings you need beforehand. NOt always easy. But it works great.

[Paul McGaha]

I like spiral duct, that's what I used.

PHM

[James Baker SD]

I also went with metal Nordfab, but I could not figure out what I needed beforehand. So my system just sort of grew starting at the cyclone and creeping along the ceiling toward its various destinations. I would order a few pieces that I knew I needed, install them, then measure what I actually had, then plan a little more growth and place another order. Install it, measure it, and plan a little more creep. Not efficient time wise, but with the weird shop I have, multiple height levels to the ceiling and obstacles to be dodged, it was the only way for me. Sometimes a 90 degree or 45 degree elbow or wye would split the degrees of direction change amoung vertical and horizontal planes, and I just wasn't up to doing the trig to plan the system. Shipping charges did not seem that much worse with the smaller orders as some vendors ship free if your order is over $75 which is easy to reach with Nordfab.

[Paul McGaha]

The results of the poll are Metal-24 Votes to PVC-10 Votes at the moment. I'm surprised, I thought most people actually used PVC for their piping.

Just based on what I've seen here on the creek. Seems like most of the time I've seen a shop tour or pictures of a dust collection system install the owner was using PVC.

PHM

[Curt Harms]

I suspect there are two primary considerations.


Cost and availability. PVC used to be the clear winner here. Today I'm not so sure, it depends on what you have locally. S&D PVC pipe and drainage fittings with more gradual sweeps are not always readily available. If you want any size other than 4" or 6" in PVC, good luck.
What we're comfortable working with. I am happier working with PVC. Someone else may prefer working with metal. 6" blast gates are difficult to find for PVC but they're easy and cheap to make.


I think the static explosion/fire argument has pretty much been put to bed. Static discharge with PVC is a consideration but can be alleviated by wrapping with light gauge wire and grounding any plastic flex hose. Do what you're comfortable with.

[Ole Anderson]

Very interesting results, at first PVC was ahead, but a huge turnaround for steel. I always felt I was in the minority for using steel. Appears not so.

[Wade Lippman]

Very interesting results, at first PVC was ahead, but a huge turnaround for steel. I always felt I was in the minority for using steel. Appears not so.

Yes it is interesting.
But I am going with PVC anyhow. Those who use it made a better case for it than those who used steel. Steel IS probably better, but PVC is cheaper and easier.

[Ole Anderson]

I keep hearing that PVC is cheaper and easier. I am not convinced. Has anyone done both that can make that as a fair statement?

[Larry Browning]

Maybe others will not agree with me, but I have metal for a short distance from the DC unit in one room going into the main shop area. Working with the metal was a royal PITA for me. Cutting the metal ducting with tin snips was difficult keeping it straight and I cut myself on the sharp edges more than once. Also at the time I built mine PVC was considerably cheaper, but that may have changed now days.

[Ole Anderson]

Maybe others will not agree with me, but I have metal for a short distance from the DC unit in one room going into the main shop area. Working with the metal was a royal PITA for me. Cutting the metal ducting with tin snips was difficult keeping it straight and I cut myself on the sharp edges more than once. Also at the time I built mine PVC was considerably cheaper, but that may have changed now days.

I can see where cutting PVC with a chop saw would be easy. Although with metal, I avoided tin snips as much as possible, same reasons as you. I took a piece of ply and with a circle cutter made a circle for each size of duct, then slid the duct into the hole, used a marker to mark the duct around its circumference using the ply as a guide then used an angle grinder with a thin cutoff saw to make a starting hole for my jigsaw to finish the cut with with a very fine metal cutting blade. Used a cratex wheel to deburr. Sounds more complicated than it really was. Currently our local HD has 6" 26 ga snaplock for $1.64/ ft.

[Ken Fitzgerald]

I used metal because I live in a very arrid area. Our total average annual moisture is 13". 3 inches less we'd be desert. I don't like static shocks. Now that I am the recipient of a cochlear implant for my left ear, not getting static shocks is even more important as they can destroy the implant and further surgery could be necessary.

That being said.....make sure you get at least 26 gauge metal. Our own John Keeton accidentally got some 30 gauge mixed into his purchase at his local Borg. When he fired up his Oneida DC.....well......click on this link and scroll down to post #43 and look at the photos..... http://www.sawmillcreek.org/showthread.php?79131-And-the-fun-begins-yet-another-DC-project!/page2

[Wade Lippman]

I can see where cutting PVC with a chop saw would be easy. Although with metal, I avoided tin snips as much as possible, same reasons as you. I took a piece of ply and with a circle cutter made a circle for each size of duct, then slid the duct into the hole, used a marker to mark the duct around its circumference using the ply as a guide then used an angle grinder with a thin cutoff saw to make a starting hole for my jigsaw to finish the cut with with a very fine metal cutting blade. Used a cratex wheel to deburr. Sounds more complicated than it really was. Currently our local HD has 6" 26 ga snaplock for $1.64/ ft.

I planned on using a bandsaw, rather than a chopsaw. Any reason that wouldn't work?

Must vary by location; my local HD doesn't carry anything. HVAC supply house is $2.20/ft.

[John McClanahan]

Don't cut pipe on a bandsaw unless it is clamped down! Once the bandsaw cuts through the pipe wall the teeth will grab the pipe and spin it at high speed. Don't ask how I know.

John

[David Kumm]

A metal cutting blade in either a chop saw or a cutoff saw works just fine. Get a little smaller blade so the pipe fits under it and cut as far as it will go. Turn the pipe 1/4 turn or so and cut again. You will get all the way around and have a good cut. Makes cutting spiral easy too. I've cut up to 10" that way. Dave

[Hank Hill]

I think metal ducting is best but I voted PVC based on ease of use, cost, and availability.

[Wade Lippman]

Don't cut pipe on a bandsaw unless it is clamped down! Once the bandsaw cuts through the pipe wall the teeth will grab the pipe and spin it at high speed. Don't ask how I know.

John

Wouldn't it be even worse with a chopsaw?

I suppose making a clamp would be doable.

[John McClanahan]

You might think so, but I had no problems with cutting PVC with a miter saw. Cut, turn and cut some more.

John

[Curt Harms]

I think metal ducting is best but I voted PVC based on ease of use, cost, and availability.

I don't have first hand experience with them but I believe plastic piping is not permitted in commercial applications. Materials quantities and velocities are a bit different than home or small commercial shops. To say a hobby shop should operate by the same rules as a large commerical operation is like saying a farmer with a 5000 bushel granary should operate by the same grain dust control procedures as one of Pillsbury or Cargill's grain elevators. Would it be a good idea to consider what 'the big boys' do and adapt as appropriate? Sure.

[Ole Anderson]

One more note on cost. In looking at Ken's referenced posts for moderator John Keaton's system using 26 ga snaplock (HVAC) back in 2008, John made this final comment:

"Hope this primer on hvac duct is helpful. The total cost of the duct system, tape and silicone, flex and various fittings, but not counting the replacement of 4 sections of collapsed 30 ga, was about $425 - substantially less than spiral, or even PVC. All in all, I would do this same system again and wouldn't hesitate on the hvac vs. the others."

And Hank, is your comment and vote based on personal experience or are you repeating what you have read on the Internet? Not saying it isn't so, just asking. We need to take such statements with a grain of salt unless someone has documentation or personal experience. Reminds me of the current TV ad with the gal saying everything on the Internet is true because the Internet says so, as her "french model" neanderthal Internet date comes walking up.

[Michael W. Clark]

I don't have first hand experience with them but I believe plastic piping is not permitted in commercial applications.

That is correct, dust codes require ducts to be constructed of conductive materials when handling combustible dusts, such as wood dust. I haven't looked for it as I only work with industrial systems, but to my knowledge, there is no distinction between home/hobby/light commecial/heavy commercial/institutional/industrial/farm, etc.

Wood Processing and woodworking has its own code and it distinguishes between "systems" (not fan capacity) rated for less than 5000 CFM and those above 5000 CFM. It also divides these groups into open type collectors (baggers) and enclosed collectors (baghouses and cyclones). There are different rules that apply to each of the four groups. Bagger systems less than 5000 CFM would be relatively easy to comply to, not so true for cyclones. My thought is the code was written this way to lessen the requirements on the small shops and because they probably have a much lower incidence rate (if at all).

It may be the code, but who is going to enforce it? Sure, if there is an epidemic of home shop DC explosions, its going to get attention, same for small farm grain elevators. The reason the big boys invest is because it is required and if they do not, they stand to loose more if there is an event. Both in terms of property damage, lawsuits, bad publicity, reputation, injuries, etc.. Plus, they are handling such a larger volume of material, that the likelyhood of an event is much more probable. Is the NFPA conservative, absolutely. However, if there is something in there that makes a system "better or safer" it may be worth doing.

Metal duct has been the standard for a long time in industrial applications before there was NFPA code requirements. There are other reasons that it is used other than it being conductive.

Mike

[ian maybury]

Interesting to see the flattened 30G ducting Ken - you hear about the possibility, but wonder if it's for real.

A jigsaw with a very fine tooth T118G Bosch HSS metal cutting blade (for 0.5 - 1.5mm sheet metal, the tooth pitch is about 0.7mm http://www.ebay.ie/itm/5-x-BOSCH-T118G-HSS-METAL-JIGSAW-BLADES-SHEET-METAL-NON-FERROUS-METALS-/320925078511 )works very well on metal ducting - but it has to be the fine toothed version run with no pendulum action.

The cut line needs marking so that you have something to follow - wrap a piece of card around the duct, and use an indelible marker. It's worth making a cradle (two U shaped brackets separated by about an 18in spacer to clamp on the bench) to support the duct while cutting - it makes it easy to rotate the duct into the blade when cutting so you don't need to move the saw.

ian