Should I do this (ductwork)?

[Tom Slick]

If the intake and exhaust are in the same room the room pressure will remain neutral. it will not suck air in from another room.

If I were designing your layout I'd put the filter at the intake of the blower on one end of the room and use the ducting as exhaust and duct it to the other side of the room (as practical). That way dirty air goes though the filter first, then "clean" air continues through the blower and out the duct. By having the exhaust on the other side of the room you create a cross flow that guides airborne dust back at the filter. The exhaust is a much more powerful "air mover" then the intake is.

duct size should be dictated by the blower's CFM rating and the desired air velocity from the exhaust duct.

[billfrommich]

Regarding several points brought up by Tom Slick (I apologize for not knowing how to use the forum's quote function).

"If the intake and exhaust are in the same room the room pressure will remain neutral. it will not suck air in from another room."

I believe that's true in the sense that it will not suck air in from another room without returning air back to that other room as well, otherwise the pressure in one room would rise continuously while the pressure in the other room dropped continuously. But if the other room is connected to the shop through leaks both "in the duct" and "out in the shop", then the pressure differential will create an airflow (and possibly undesirable dust transport/infiltration/accumulation) within and between the other room as well. Also although what you assert seems theoreticlly correct as regards net exchanges of air, it would seem to imply that I needn't concern myself with sealing the doors that separate my shop from the rest of the basement, but I have a hunch that in that case there would be some movement of dust from the shop into the rest of the basement.

"If I were designing your layout I'd put the filter at the intake of the blower on one end of the room and use the ducting as exhaust and duct it to the other side of the room (as practical). That way dirty air goes though the filter first, then "clean" air continues through the blower and out the duct. By having the exhaust on the other side of the room you create a cross flow that guides airborne dust back at the filter. The exhaust is a much more powerful "air mover" then the intake is."

I believe that either of the two approaches I described above achieve the identical ends of 1. having filtered air (as oppossed to dusty air) passing through the blower and 2. having filtered air exhausted into the shop at one end and taken into (sucked into) the filter at the opposite end of the shop. I think the approaches differ in the pressure situation "in the duct" vs."out in the shop ".

"duct size should be dictated by the blower's CFM rating and the desired air velocity from the exhaust duct"

I agree but as a practical matter I believe in this situation you would want the highest CFM as possible (without burning up the blower motor) to achieve the highest air overturn rate possible in the shop. Typically this involves increasing the cross -sectional area of the duct which tends to produce a decrease in air velocity (FPM) within the duct - but since the duct air has ostensibly been filtered down to micron level I have a hunch (haven't crunched the numbers though) that the FPM in the duct would still have adequate "carrying power".

[capncarl]

If you are just going to be using it for and air duct and it is the same humidity as the rest of the house air, just caulk up all the cracks in the boards and joints and paint it. It should stay as clean as a metal duct.

capncarl

[Kristofor]

Or as dirty as metal ductwork

But, from the perspective of someone living in an area that does have basements I have seen this method of cold air return construction on newer houses that ranged from $200-500K. While it looks cheesy to me, and feels like there should be more internal resistance, it's apparently still allowed (or was as of 2-3 years ago).

If you have your filter near the blower at the "head" end there wouldn't be any negative pressure in the duct to try to suck dust in from the floor above. If you have the filters at the head end of the run and the blower at the exhaust you could have some negative pressure once your filters get very dirty. But I doubt under normal use that it would become much of an issue.

[dbhost]

I don't understand this comment. The size (CFM capacity) of a dust collector has no direct relationship to the size of the shop space it's serving. What do you mean?

Sorry it wasn't clear. What I meant by WAY oversized, is... Any of the DC systems I have seen that will have the 6" port, tend to be physically much larger than say your 2HP HF DC unit.

I think what people were probably trying to say is that while a shop vac-powered DC system can help you keep a cleaner shop, it's not going to do anything much to protect your health. The reason is that no shop vac can move a sufficiently large quantity of air to collect all the fine particles right at the source, where the dust is being created. Unless that can be done -- and my HF "2HP" DC with 4" hard piping can't do it, either -- the fines will escape into the shop air and eventually find your way into your lungs. A shop vac like yours and smaller dust collectors like mine can indeed do very well at chip collection, but they're lousy for bona-fide dust collection.

Agreed to a certain point. Even the giant twin cylinder 3+ hp models don't have enough suction to effectively remove all the fine dust. Take a CMS for example, they tent to fling pretty much everything everywhere, far enough away from the DC port and chutes that the suction from the DC isn't going to be effective unless it also starts sucking the nuts and bolts off your tools... Which is why you also need an air cleaner of sorts. I am making do with the 20" box fan w/ the 20" filtrete filter duct taped to it...

In the research I have done, the testing that I have read about was to run the air filter / fan assembly for a few minutes to scrub the ambient dust out... Then run a dusty operation with the fan and DC system running. Then kill the lights and shine a flashlight through the air to see how much suspended dust is in the air...

Using my Random Orbital sander, and this process, my shop has cleaner air after sanding than prior to starting the procedure.

During ANY particularly dusty operation, I still use a dust mask. And I would do the same thing with that HF DC system, or even a monster 8" Grizzly 3HP cyclone system...

As far as fine dust collection is concerned. The HEPA filtration of the Ridgid, with it's .3 micron filtration rating, certainly is better than the 30 micron filtration of that HF unit... I am NOT slamming the HF unit in the least, that is a decent, competent DC unit.

I could stand to be corrected here, but I don't think there is any ONE single product solution for complete dust control. The systems I have seen in pro shops are all plumbed DC units with air filtration systems of some time. (The big Jet is REALLY popular it seems)...