PVC vs Metal duct


sbarton22

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I just got my dust collector wired and running. I'm pretty amped about the whole thing...so much that I now want to run a trunk line in my joists to collect from another part of my shop.

My question is this...can someone give me a few pros and cons of PVC vs Metal duct?

I understand that I need to run some grounding wires in the PVC. Doesn't seem like a big deal. Would I need to ground metal duct?

Any advice here would be greatly appreciated.

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I had 4" PVC. I just finished ripping it out and replacing it with 6" metal. I had lots of trouble with the seals on my old PVC for some reason. I never bothered to ground my PVC.

I got a new collector and needed to switch to 6". Honestly the metal was much easier to work with. It's much lighter and easer hang and join together.

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I just got my dust collector wired and running. I'm pretty amped about the whole thing.

Cue rim shot. ;)

I understand that I need to run some grounding wires in the PVC. Doesn't seem like a big deal. Would I need to ground metal duct?

Aagh! Like the Kraken, the dreaded "grounding PVC" legend rears its head once again.

Short answer: No, PVC pipes do not need to be grounded. Long answer: Visit Dr. Rod Cole's excellent article on the topic.

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Rob-- after many hours of reading last night, I came across that. I will fall into the safe zones he references in a couple of ways...I'm pulling 1450 CFM, and he mentions 1500. He mentions 20' @ 4" won't level a shop, I'll be right about that distance. However, he just doesn't come off all that confident in some of his research enough for me to risk my home over it. I do now understand that you never actually ground the PVC.

Right now, I think I am loving the idea of spiral pipe as the trunk line, but integrating PVC into other areas closer to the tool...say as part of a tool stand. I think there are giant advantages to PVC there. I also think hanging a metal pipe by myself sounds a lot easier than messing around w/ PVC. It is also easier to reconfigure, should the occasion arise.

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Hi Barton

I am not sure if this will be of help to you but this is my cost in Phoenix, Az

4” x 10’- 28ga spiral duct run about $1.28 ft.

4”Connectors $ 3.50 each

4” long sweep elbows $5.50 each (each elbow add 4’ to SP )

4” end caps $2.50 each

4” metal wye $6 to $10 each

Hard cast (duct sealer) $ 18.00 +-

You will also need some sheet metal tools $50 to $75

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Plan on getting static shocked regularly with PVC less so if grounded. Static shock gets old after awhile and grounding is not a 100 percent cure especially on machines that make a lot of dust.

Don't use the cheap metal like the home depot or penstate stuff. I still have a pile of it laying behind my shop that the cyclone sucked flat.

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Hi Barton

I am not sure if this will be of help to you but this is my cost in Phoenix, Az

4” x 10’- 28ga spiral duct run about $1.28 ft.

4”Connectors $ 3.50 each

4” long sweep elbows $5.50 each (each elbow add 4’ to SP )

4” end caps $2.50 each

4” metal wye $6 to $10 each

Hard cast (duct sealer) $ 18.00 +-

You will also need some sheet metal tools $50 to $75

Wow!! This is the perfect list I need. I found a supplier earlier, and this is fills in the gaps!

This is going to sound like a really stupid question. As an architect, I've seen guys working on spiral pipe in the field and they have them uncoiled a bit. They don't come that way, do they?

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Add me to the list who started with 4" PVC, and ended up with 6" metal mains to 4" metal drops. The metal pipe is pop-riveted together and sealed with metal (not cloth) duct tape. I'm really happy with the metal pipe.

While you're at it, spend the extra money for METAL blast gates. I replaced several cracked plastic gates. I've never had a metal version fail.

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  • 2 weeks later...

Penn State Industries has a design service for $100 and they give you $50 back if you buy the pipe from them. I used it and it worked out great, especially if you're not familiar with how the pipe all works together (inside vs outside couplings). I used the heavy gauge steel pipe and it wasn't too bad to work with. I sealed it up with duct and aluminum tape and they both worked fine with no leaks. I used 6" mains on a 3HP Grizzly Cyclone and can run multiple tools at a time without a problem.

The area I ran the pipe is about 40x40 and all in it cost more than the DC

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wow...I don't feel like I am anywhere near those numbers. I ran a short run near the DC with 3 drops for maybe $60-70 all in on the ductwork. I'm getting ready to buy spiral pipe for another run across the shop with 2-4 drops, and I don't see the first drop costing more than $60, and each additional being in the $25 range.

Maybe I am doing something wrong?

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I did a two blog posts on selecting my cyclone and then the duct installation.while it's not all applicable I think you'll find some good info there. There is a chart that shows what gauge spiral pipe you need for what static pressure. Bottom line is that you will be fine with 26ga spiral that you can buy from a local HVAC supplier. You don't need to spring for the 24ga stuff that the dust collection guys are pushing. I found spiral to be much easier to work with than snap lock. Using to right tape is key too. All the info is here:

Http://www.gunpowderwoodworks.com/blog

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I found a very easy way to cut the spiral pipe - use a jig saw. There are details on my blog. With spiral all you have to do is cut to length and tape it up (or rivet if absolutely required). No crimping required. The spiral also is stronger due to the spiral seam and much harder to dent. For the same strength in snap-lock you have to step up the gauge of the metal which costs more. The only advantage to snap-lock is shipping costs.

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I have found through testing and errors that most snap lock pipe is fine if at least 26 gauge. Currently the big box stores stock 30 gauge and it will collapse when the gates are all shut and the DC is running. You can over come this with anti crush rings (piece of plywood with hole in the middle) but it adds to the install time. The other option. Is a "vacuum safety device", I made mine from a T fitting and a mdf "valve" on the top. This way the valve stayes closed as long as one of the blast gates is open. When I close a blast gate the vacuum opens the "valve" and reduces the internal pressure. It also opens partly if I am. Using a 4" drop, main drops are 6", so it maintains the proper CFM flow through the main trunk. I will try and get a picture of both and post them here. My cyclone is a 5hp Clearvue.

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I found a very easy way to cut the spiral pipe - use a jig saw. There are details on my blog. With spiral all you have to do is cut to length and tape it up (or rivet if absolutely required). No crimping required. The spiral also is stronger due to the spiral seam and much harder to dent. For the same strength in snap-lock you have to step up the gauge of the metal which costs more. The only advantage to snap-lock is shipping costs.

Another option is an angle grinder with a cut off wheel, for me this was the easiest and quickest. A few rivets and wrap of metal tape and the connection is done. One important aspect in using metal pipe is the ease of retrofitting in the future
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