Ducting size question

[Sean Walker]

I am looking to purchase a Grizzly G0548ZP pretty soon and want to re-do my current ducting. I currently have a harbor freight D/C but find that it lacks the cfm for my needs. My only issue is, my separator trash can only has 4 inch ports on it, and I was wanting to go with a 6" main line. Would I lose any by keeping the D/C at 4"? I read elsewhere that the more cfm's, the bigger the main line should be.

Thanks again

[John Donhowe]

I read elsewhere that the more cfm's, the bigger the main line should be.

It's not so much "should be" as "can be". Large ducts will have less resistance to air flow (good), but for a given air flow (cfm), air speed (fpm) is less (bad). You should have 4000 fpm air speed to keep dust particles from dropping out- small DC's can't produce enough airspeed with large ducts. Airspeed = air flow/duct area.

[marty shultz]

I don't know the specs on your DC but a 4" main doesn't allow for much flow. You may not see a significant difference between the two DC's if you stay with the 4".

[Sean Walker]

I don't know the specs on your DC but a 4" main doesn't allow for much flow. You may not see a significant difference between the two DC's if you stay with the 4".


Yeah i'm upgrading to 6" main after talking to penn state industries.

Thanks again

[Jim Andrew]

I'd look at getting a cyclone rather than a bagger, and nothing less than 3 hp.

[Sean Walker]

I'd love to but for my needs, the 1700 CFM is plenty for 1 tool at a time and a 15' run. I am also trying to save that extra money for another tool purchase lol.

[David Ragan]

I have the smaller of the two ClearVue. Went from all 6" duct to about 6'of 6" followed by two 90* corners and 15' of 4". Man, what a difference! I was worried about static drop, and it is no problem whatsoever. My issue was that before, with the hodge-podge stringing up wyes and ducts/blast gates, etc over the years, it led to a lot of leakage.

So, this time, after I secured the pipes/flex duct with selftapping small bolts, I wrapped the joint in that clear 4" wide shrink wrap or some white duct tape to ensure no leakage.

Now, the system screams suction down at the end machine. Of course, the TS, BS, and planer have 6" fittings. I did not enlarge the 4" intake off any machines. Planer has about 8' run of 4" going to it.

I am really happy with the improvement---one good thing about a small shop, great dust collection.

[David Utterback]

Agree that 1700 cfm is sufficient for single machine use. Unless you have long duct runs and lots of elbows and/or intersections, the upgrade to 6" may not be that important. John identified the important factors above. With 1700 cfm, 6" would have more than sufficient duct velocity. 4" would have even higher velocity but greater frictional losses that lower the volume to some extent. You may want to test with the 4" that you have before making the switch.