Ductwork Choices for Dust Control

A woodshop owner considers the cost and value of PVC ducts as compared to various metal duct options. January 3, 2012

I'm entering the final phases of setting up my new shop and am researching ducting to use with my Clearvue 1800max (aprox 1900cfm, 5hp, 16" impeller). My first choice is using Nordfab, smooth interiors, wyes, and branches designed with 30 degree sweeps enabling large radius transitions, and large radius elbows with 2.5"ird, all adding up to a very efficient and affective duct system.

After drawing out the ductwork and figuring all the fittings/pipe (I did spec it out with the pricey 60 degree tubed elbows to come off the 30 degree branches which enables the smoothest flow of air) the cost came to about $3400.00. In of its self not a huge cost for all the benefit but after building, moving and resetting up, I'm being conscious of not overspending. I refigured my duct needs using PVC.

My second choice is PVC, due to its very smooth interior and ability to create large radius transitions and elbows (using 22.5's and 45 degree fittings) also researching PVC it seems the drawbacks are mitigated if the blower and ductwork are sufficient in power and size to keep the interiors free of build up, and static can be reduced using some creative grounding. The PVC cost is about $600.00, quite a substantial cost savings and still seemingly an effective/efficient duct system.

It seems PVC is a better choice for me over standard metal duct due to its smoother interior and also having more flexibility creating the larger radiuses and transitions (better air flow). Some of my duct needs are 8", most is 6", and a few transitions down in size. In my new shop I will be working in a closed environment for four-six months a year due to the weather so air flow/filtration is my primary concern in setting up my dust collection. It doesn't seem the cost of the Nordfab is justified, since can create an as effective duct system using pcv for 3k less. Any thoughts or insights would be greatly appreciated.

Forum Responses
(Dust Collection and Safety Equipment Forum)
From contributor F:
Well although PVC may be fine for hobbyists, not quite the same thing for a pro shop. Although regulations are different all over the country, I'd be surprised if you could use PVC anywhere. Talk to someone who knows your local regulations before investing in a system that you may end up having to tear out down the road.

Don't overlook spiral pipe. Although the Norfab stuff is very nice, it's also about two-three times the cost of spiral. You can get the long radius 90's with spiral also, but I doubt you'll see much difference. I used the regular 90's on my system and they're not a problem. If youíre a one or two man shop you'll only be using two machines at most at a time. Your cyclone should be able to handle that with regular 90's without any problem (unless you have extraordinarily long runs). My system cost about $3k and goes from a 12" main to as small as 3" with nine drops.

From contributor G:
It seems like you are going from one end of the spectrum to the other. Why only consider high end Nordfab or cheap out with PVC. Sounds to me like standard metal ducting would be best for you. What are the large radius PVC elbows like? Two standard short stubby 22.5s or 45's with or without a length of straight pipe in between do not make a large radius elbow.

Recommended radius is at least 1.75 times the diameter being used. Maybe you are considering true large radius one piece elbows that I am not aware of. I have never heard of PVC having an advantage over metal because of inside smoothness. Did you price out regular metal duct (spiral or snap lock)? When you get to 6" and 8" PVC it is not less expensive than metal. I used 4" PVC in my first shop years ago and while it worked, I wouldn't go back to it.

From the original questioner:
Yes price is a factor but the reason for choosing both the Nordfab and the PVC over spiral/snaplock pipe is their ability to deliver the air with the most efficiency, that along with the large centerline radius of the elbows coupled with the effective design of the wyes and branches (Nordfab) seemed to me to be the best choice for maintaining air speed which helps with capturing the fine particulate (at least thatís how I understand it).

I realize that creating sections out of 22.5s and 45's isnít a true large radius tube (like the Nordfab) but it does increase the diameter of the curve the air is traveling through, creating less friction. Although I could build similar curved sections with standard spiral/snap lock metal pipe, the PVC seemed better due to its slick interior.

My intent is to create an effective duct system. As stated previously I thought the Nordfab was the best (due to tech. specs.) but am hesitating spending that much when there might be a close second (in tech. spec.) for considerably less cost. If the science isn't valid for backing up the PVC then it makes sense the comparable second choice to the Nordfab is the standard metal duct.

From contributor J:
Where can you get spiral metal pipe for about 1/3 the price of Nordfab pipe? All of the literature I have the cost of spiral is only marginally less expensive. The one time I priced a system, the only difference in cost between all the spirals out there and Nordfad was the cost of the quick clamps.

From contributor G:
I purchased my spiral pipe from a company in Minneapolis, MN appropriately named Spiral Pipe. They supply to professionals and were not willing to design a system for me.

From contributor F:
The truth is no matter how good your DC is you will still need air filters to get the stuff that escapes. Not to mention the dust that's on the boards and other products as you bring them into the shop.

I have some of the Quick lock stuff and it is very nice, but I wouldn't say it's more effective than spiral. In fact I might even say the opposite. Quick lock is dependent on rubber or silicone seals to keep it airtight. It seems possible that with jarring from being bumped into and constant vibration from machinery these seals could fail over time. I know the stuff I picked up had several seals that were not seated properly upon disassembly. Spiral on the other hand if installed correctly will have all the joints screwed or riveted together and taped, meaning airtight until it's taken apart.

I won't get into the number crunching aspect of this stuff as it's mostly over my head. I would say though that if you have a cyclone with enough power, the minute losses youíre attributing to elbows and such will likely be irrelevant. You didn't say if you have employees, but if not a 1900 cfm (even assuming exaggerated manufacturer specs) system should move more than enough air for your purposes and the different piping will likely make no discernible difference. For instance a 24" drum sander requires somewhere in the neighborhood of 600 cfm. Assuming your collector pulls a true 900 cfm, you could still lose 100 cfm to duct and have plenty left for the machine.

My advice would be to run your duct and not worry too much about those elongated bends. Instead you could spend a little extra time trying to improve the efficiency of the collection on each of your machines.

From the original questioner:
I understand the futileness of chasing down every last dust micron, although with the new machine ports I'm having made, the increased duct size and the more powerful cyclone, I'm going after as many of those rascals as I can! Also after milling how about leaving the cyclone running with blast gates open to filter the shop air?

Thatís interesting your observations regarding the seals on the Quick lock (Nordfab?). I agree and also prefer the screwed and tapped joint of the standard fittings/ pipe for the reasons you address. For me the Nordfab is appealing due to its smooth interior along with the very well designed wyes, branches and elbows. (I don't need the quick lock feature).

I do use help when needed but prefer and usually work alone, that being said I do like to leave the band saw and jointer running at the same time with both 6" dust ports open when milling veneers. Also my tablesaw will have two separate 6" branches feeding it. I'm confident my system will adequately meet those requirements, and having a well designed and efficient duct system is an important element of that setup.

From my research it seems PVC is a viable efficient material to use for duct but there also seems to be plenty of controversy surrounding its use. Since my shop will be seen by clients, architects, and builders (possibly inspection from homeowners insurance) I canít justify the risk (if only perceived) of using PVC and will set up with a quality metal duct.

From contributor F:
I've heard about guys leaving the cyclone running to try and filter the shop air, but to me it sounds like an impractical idea at best. You'll be using a 5 hp motor to draw air through one or two specific points in the shop, as opposed to having a 1/3 hp motor physically circulating and filtering the air. I have three air filters in my shop and they do a very good job at filtering the air quickly.

I use a 7-1/2 hp cyclone with a 7" and 4" drop ungated. The 7" splits to 2 - 5" ducts, 1 for each of my tablesaws. The 4" splits to 2 - 3" for 2 overarm guards. This is more air than typical for a tablesaw. Even with this setup there is dust that escapes, it is very difficult to counteract the force with which the blade throws dust at the very end of the cut. I'm not sure I see the benefit of using 2 - 6" drops on a single saw? Where and how are you planning on attaching?

I applaud your trying to design a top notch system - too many guys are short sighted in this area. I think if your cyclone is a well built unit you'll be fine with regular spiral duct. As I said on my 7-1/2hp system there is a 7" and 4" drop always open. The rest of the gates are open as needed and I have had two other 6" ports open without noticing any significant loss of suction. I think the elongated elbows are much more important for guys trying to get by with two or three hp systems. Iím avoiding the use of the flue. I hard-piped half my equipment and the rest where it needed to have flex, (things like planer hood), has as little as practically possible.

From the original questioner:
For cleaning the air I was thinking of leaving more gates open which would actually draw from both ends of the shop. When I'm set up I'll experiment and repost results.

Sorry for the confusion, my t-saw will have two 6" lines feeding it one staying 6" to the base cabinet and the other up above which will then reduce down to 4" to use over the blade and shaper if needed.

I went to my local HVAC supplier and went over my duct needs. I've decided to spec out with the same angles that Nordfab uses for their wyes, branches and elbows. My main 8" y will have a 60-degree angle between the two arms and will use 60-degree long radius elbows (2.5" CLR) to complete the 90 degree change in direction. The branches (8x6x6, 6x6x6, 6x4x6, 6x3x5, 4x4x4) will all branch at 30-degrees and will use the 60-degree lr elbows to complete the 90's. These softer angles will allow for a more even pull/flow of air through the wyes and branches adding up to a more effective, efficient draw/duct system. I will use spiral pipe for the straights (for strength). It seems the seamed snaploc pipe has a smoother interior but Iíve been advised not to use it due to its inferior strength?

With this system I'll get the technical specs I wanted from the Nordfab (except the laser weld) without the expensive quick link. The duct seems to be a very important element of an affective dust collection system and for me is well worth the extra effort.

From contributor M:
Why not just use furnace ducting? I looked at some of Oneida's ductwork, and almost fell on the floor when I compared their price to standard 8" furnace pipe. I ordered 5' lengths from my local plumbing supplier (5' were cheaper than 2- 2' pieces). I had them order some 8"-6" y's also. It may be a little more work to assemble than the clamp together stuff, but the money savings is well worth it. As for air leaks -duct tape, go figure. While efficient dust collection is necessary, spending $3k on ductwork will not give you the return it will if you spend 1/3 of that on ductwork, and spend the other 2/3's on machinery that produces the product you sell.

From contributor G:
Furnace duct is lighter gauge (thinner metal) than duct used in dust collection. It is possible to collapse ductwork that is too thin when most or all the blast gates are closed. The y's have too small of a radius and rob the system of efficiency. In my experience duct tape will eventually fall off in a couple years. While furnace duct may marginally get the job done, you are not comparing apples to apples compared to real dust collector pipe.