# Ducting size increase



## laldog3 (Mar 20, 2011)

I'm thinking of increasing the size of my duct work from 4" PVC to 5" metal duct. It presently is about a 10" run with a drop to my chop saw and another drop that is connected to either a router, sander, or planer (by way of a 4" expandable hose.)
Has anyone done this and what kind of increase in performance did you experience?
Any tips and insight would be appreciated.


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## TomCT2 (May 16, 2014)

for collecting sawdust and chips, diameter is not the issue - air flow in feet per minute is.
increasing the diameter will slow the air flow.
so the question is: what problem(s) / issue(s) are you trying to solve?


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## laldog3 (Mar 20, 2011)

I would like to increase suction, or the effectiveness of the dust collection


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## DrRobert (Apr 27, 2015)

Dust collectors are about CFM’S not suction. Shop vacs are about suction.

What is the size if the blower? Anything over 1 1/2 horse will be choked down by 4” pipe. Air flow doesn’t mean much if it can’t pick up the material.

You need a good sized blower and the right setup to collect a miter saw.


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## laldog3 (Mar 20, 2011)

DrRobert said:


> Dust collectors are about CFM’S not suction. Shop vacs are about suction.
> 
> What is the size if the blower? Anything over 1 1/2 horse will be choked down by 4” pipe. Air flow doesn’t mean much if it can’t pick up the material.
> 
> You need a good sized blower and the right setup to collect a miter saw.


I've got the ever-popular Harbor Freight 2 HP with a cartridge filter upgrade.


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## BigCountry79 (Jun 2, 2021)

@dbhost and I are both in the process of upgrading to 5" duct. The math on the upgrade shows a significant increase in airflow.


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## DrRobert (Apr 27, 2015)

6” will work even better.


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## dbhost (Jan 28, 2008)

The charts I have seen say that 5" is as close to ideal as you are going to get with a 2HP blower. And at least stock, the HF 2HP has a pitifully small impeller that further reduces its effectiveness. 

Mine is upgraded to a Wynn cartridge filter, Wen impeller, and Neutral vane to insure it is as efficient as possible although I DO blow down my filter after every use.. Doesn't take but 30 seconds, and the compressor is RIGHT THERE next to the DC so why not?

Anyway, I am going with 5" as it will support maximum airflow while retaining suction, going larger reportedly nets more CFM at the cost of suction. It's kind of a sweet spot thing.

IF I had ANY thought that I could possibly fit say like a ClearVue CV1700 or something like that in my shop, which I simply do not have the headroom, I would have gone with 6", but I fully intend to, unless I hit the Mega Millions someday and can afford pipe dream shop type stuff, I fully intend to stick with the 2HP HF DC and try to maximize my minimums as it were...

What I can tell you, is if you chose to go with 5", you are either NOT going to be able to go full on metal ducting, OR you are going to pay a fortune for it. All because the 5: branch wyes are very rare. I have only seen them in one particular brand whose name escapes me right now, and they are around 40 bucks a piece. 

So I am going for a blend of metal / ABS Plastic. To get things to fit nicely means I have to bang out the crimps on the ends of fittings, and use LOTS of HVAC tape to seal it up.

Oh, and FYI, Orient your crimps backwards from how you would an HVAC system, remember dust collection systems PULL not PUSH, and you do not want your air, and worse, shavings running into the open end of those crimps!

I have other more pressing projects but within the next couple of weeks, I am going to get to HD and grab the rest of my materials to get this job done. Will post about it when I finish...


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## dbhost (Jan 28, 2008)

TomCT2 said:


> for collecting sawdust and chips, diameter is not the issue - air flow in feet per minute is.
> increasing the diameter will slow the air flow.
> so the question is: what problem(s) / issue(s) are you trying to solve?


This statement is not necessarily true. Increasing the duct size to within the tolerances of the blower will remove restriction and INCREASE CFM, but will drop static pressure (vacuum).

There is a tip over point though, so increasing beyond the capacity of the blower will actually cause your CFM to drop.

LOTS of users are running with Harbor Freight 2HP dust collectors connected to 6" mains, in order to make this happen they have to modify the intake flange on the impeller housing,just to make the connection, and they are operating beyond the parameters of a 2HP blower. 

Does it reduce real world performance?

I honestly do not know, I just know the charts and articles I have seen. And they seem to agree that for a 2HP blower, go with a 5" duct, so that is what I am doing.

You WILL have issues connecting 5" to your tools as most tool ports are either 4" or 2.5". Plan accordingly.


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## BigCountry79 (Jun 2, 2021)

How hard was it replacing the impeller @dbhost ? Did you rotate the shroud while you were in there?

Also I think it may be more accurate to say that going fron 5 - 6" pipe increases cfm at the expense of velocity, and you need a minimum velocity to keep larger chips suspended, especially in vertical runs.


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## Rebelwork (Jan 15, 2012)

I think buying a better DC would be the answer.


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## dbhost (Jan 28, 2008)

BigCountry79 said:


> How hard was it replacing the impeller @dbhost ? Did you rotate the shroud while you were in there?
> 
> Also I think it may be more accurate to say that going fron 5 - 6" pipe increases cfm at the expense of velocity, and you need a minimum velocity to keep larger chips suspended, especially in vertical runs.


I have the older green model, so the impeller swap was straight out easy. Did not rotate the shroud, didn't see a need as it is the same orientation as the Wen. 

Simply unplug the machine, remove the cover, remove the counter threaded allen screw, Use a gear puller to grab the flange and press the old one off. Line up (and lightly lube) the shaft and key, orient the key UP so it doesn't fall out, line up the new impeller and drive it home with a hunk of 2x4 and a mallet, reinstall allen screw, spin to make sure no interference, reinstall cover, plug back in and test.

The gray ones I hear have a problem with a brittle flange on the impeller. I have heard of 2 cases where the flange broke off while trying to pull the impeller. That certainly would make things harder.... I know of quite a few swaps though, and only 2 issues... still worth the risk, but you will be cussing if you are issue #3....


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## dbhost (Jan 28, 2008)

Rebelwork said:


> I think buying a better DC would be the answer.


I'll gladly take donations for a "better DC", it must fit in my space, be as good as my HF DC or better, and run on the avaialble 110V circuit.


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## d.mcknight58 (11 mo ago)

A little late here, but make sure you find all your little leaks. I have changed to a powertec 5370 and a 5 inch main metal duct. after the super dust deputy which has a 6 inch outlet. The inlet is 5 inch and there is a trick to the cyclone. I used an anemometer to measure every step of my duct work. I have a recloseable 30 gallon barrel which is great. Did a 5 inch wye metal duct right out of the cyclone and ran a 5 inch line about 10 feet before knocking it down to 4inch. The blast gates you buy plastic or aluminum are leaking little devils. I maintained 4000 cfm with no problems. When you choke it down to 2 1/2 inch for some tools it just collects some but still has its velocity to clear it out. Avoid using long lengths of flexible ducting. Mitre saw is a definite issue but I have made some gorilla tape wings on mine which funnel most of it into the factory little 1 1/2 outlet. After really observing the debris left, most of it now goes straight back. Got a 4 in wye with a 2 1/2 inch which then gets chocked to the top of the mitre saw down to 1 1/2 inches. Now I plan on reduce the 4 inch down to 3 inch and mounting a movable duct to position behind the saw and see how much is left after that. Got long winded, I wanted something quiet less noise than my shop vac and can barely hear it running outside of my shop. Bigger is not better and the trick is to measure. So my blower is 4 inch and I incresed it to 6 inch for the super dust deputy. Then the 5 inch goes to my main; sounds weird but that is the trick to the cyclones. You want enough CFM to get it their but then you want it to slow down so it falls out of the airstream. to much and the fine dust will end up in your bag or filter. It works great for me. Hope it helps some one. So much information about all this and here is a great calculator online. https://www.engineering.com/calculators/air-flow-conversion-calculator/


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