Three questions about externally vented dust collection

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Forum topic by srzsrz posted 04-17-2013 09:43 AM 4414 views 1 time favorited 43 replies Add to Favorites Watch
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37 posts in 1830 days

04-17-2013 09:43 AM

Topic tags/keywords: dust collection dust collector cyclone air quality asthma dust

I’m buying a house and want to set up shop in the one-car garage. As an asthmatic, I want good dust collection and ventilation. With temperatures out here ranging about 50–70°F, I figure I can get away with a ClearVue CV1800 cyclone/blower with no filter, vented directly to the outside. I do have some questions, though.

  • Pulling 1000cfm of air out of a 2200 ft³ garage (that’s 27 air changes per hour!), how am I going to prevent backdraft from the water heater and HVAC furnace? Is it enough to cut some vents in the garage door, or do I need dampers or fans in the appliance flues? Or perhaps use another fan to forse air into the garage? And, perhaps most importantly, how would I go about measuring whether whatever I did to prevent backdraft is working out? Would a standard carbon monoxide detector suffice? What is the best place to mount it?
  • I see a lot of people install air filtration or ventilation as well as DC, to remove the “fugitive” dust. But is that really necessary if I already just paid for a “Pentz grade” system that can pull 1000cfm out of the shop? Why not just leave the DC running, pulling through, say, a floor sweep?
  • I am a strong believer in actually measuring any parameter I’m trying to control if at all possible. I already have a Dylos particle counter to measure the overall effectiveness of any dust collection and ventilation, but I was wondering what would be a good anemometer to measure air speed. Is Extech any good? I’m considering one of their windspeed/temperature/humidity combination meters, which would also come in handy for testing and tuning the home HVAC system.

43 replies so far

View Fred Hargis's profile

Fred Hargis

4949 posts in 2457 days

#1 posted 04-17-2013 11:52 AM

With a CV, can I ask why vent outside? Typically, I consider venting outside a good option for a few reasons, one being you don’t have to worry about the filter needing cleaning. But with a CV, separation is so complete that the filters stay pretty much clean all the time….negating much of the advantage of the outside vent. There are some other reasons to vent out, but none as important (IMHO) as that one. Back to the question, the furnace and water heater will have to be sealed off from the flow in some manner, there isn’t (that I know of) a way to prevent the backdraft on the appliances themselves.

Some folks report the clean the ambient air by filtering it through the DC. I suggest an ambient air cleaner, but not for health reasons. By the time the AC gets the dust, it’s already made it to your lungs. For your health, capturoing every spec at the source is your best bet. So you also need a really good shop vac for your smaller tools, and fit it with a Gore Clean Stream filter, hepa performance, robust construction, and cheaper than some alternatives. Now, why the ambient air cleaner. To just clean any residual airborne particles and keep them from depositing themselves, well, everywhere to become airborne later the next time you do something. Run it for a few hours after you leave the shop.

You seem pretty serious about DC (applause) so I suggest to measure airflow you consider using a Magnehelic gauge (cheap, $25-$30, e-bay) and a pitot tube (not so cheap, maybe $65+). This is the way the pros do it ( with DC systems). I have never bought the pitot tube, but use a magnehelic to measure when to clean my filter…but I don’t have a CV; in that case I wouldn’t worry about it. All this, of course, is just my opinion.

-- Our village hasn't lost it's idiot, he was elected to congress.

View unbob's profile


808 posts in 1867 days

#2 posted 04-17-2013 12:22 PM

In commercial cook lines with the big hoods over the grills, and ect. There is another blower for make up air.
Otherwise, heat will be sucked out of the building, and the doors will be hard to open, or be sucked open.
I am looking to do outside venting myself, and cant see a way of doing it without providing the make up air.

View crank49's profile


4030 posts in 2934 days

#3 posted 04-17-2013 01:54 PM

Well if you already bought in to the Pentz plan all you can do is plan to inject makeup air.
The only way to be sure it is working is to measure the relative air pressure in the shop v.s. the outside.
A manometer is the instrument that does this.
It is possible to provide electrical controls such that a negative pressure in the shop (created by the exhaust) will cut the power to the exhaust motor.
Good luck with trying to condition the air at 27 changes per hour.

Another fringe benefit of this plan is you will have the garage air pressure positive relative to the house; if it’s an attached garage, and will get some dust and fumes in the house.

I think Pentz is a putz if you haven’t already figured that out.

View MrRon's profile


4710 posts in 3207 days

#4 posted 04-17-2013 07:44 PM

I have stated in many of my DC threads; NO filter will remove 100% of the fine dust (the destructive stuff). Even HEPA filters won’t remove 100%. Hepa filters don’t start working effectively until they start to trap dust. As the filter traps dust, the pores in the filter get smaller and smaller, because they are clogged with effectively traps most of the dust. BUT, a clogged filter (any filter) will slow down the velocity of the air stream and as the velocity drops, so does the CFM. The result of venting to the outside is no loss of velocity or CFM. If you go this route (recommended), make sure the exhausted air can’t make it’s way back into the shop through a door or window or you will lose the benefits. It doesn’t matter which type of DC you use, cyclone or non-cyclone. It is there only to collect large particles and chips that you don’t want passing through the fan. The fan will see only fine dust.

View srzsrz's profile


37 posts in 1830 days

#5 posted 04-18-2013 05:31 PM

Thanks everybody for your suggestions!

crank49: As to conditioning the 27 changes per hour: the only reason I would even consider outside venting is because the climate is so mild around here. Average temperatures are around 50°F in January and 70°F in July. As to your opinion about Mr Pentz: do you think he exaggerates the dangers of fine dust, or the equipment needed to control it?

View crank49's profile


4030 posts in 2934 days

#6 posted 04-18-2013 07:36 PM

The equipment side. I was a foundry engineer for 30 years and designed a lot of dust control equipment for materials much more hazardous than wood, like silica, chrome and lead oxides, asbestos, etc. so I am fully aware of the dangers of respirable dust. I just think he conveniently seems to recommend a particular piece of equipment. When you want a specific solution it’s not all that difficult to adjust the facts to arrive at that conclusion. I believe it was Will Rogers who nailed it pretty good when he said there were “Lies, damn lies, and statistics”

edit: upon further investigation I find that that quote is attributed to “Benjamin Disraeli, Alfred Marshall, Mark Twain and many others as well”

View Grandpa's profile


3259 posts in 2639 days

#7 posted 04-18-2013 07:45 PM

Crank I thought Pentz designed what he thought was the best system then Clear Vue copied it or bought his design to copy. I don’t think anyone has ALL of this figured out. Pentz did a study then put his paper out there for the world to read. He stands on that. He didn’t condemn anyone. Yopu could be sitting on the shelf next to Pentz but you have had to put someone down to make yourself look good. This is not necessary if you are really any good at all. I do wish you would just put the facts out there and let us sort them out. We do have respect for you so please don’t change that image we have. Thanks

View MrRon's profile


4710 posts in 3207 days

#8 posted 04-18-2013 07:56 PM

To test the efficiency of any filter, run the DC in a dark shop at night and observe the dust that is coming from the filter in the beam of a small flashlight.

View srzsrz's profile


37 posts in 1830 days

#9 posted 05-01-2013 07:06 PM

As to Pentz: I understand your skepticism about his advocacy of one very specific design.

I think his emphasis on “this is the only way to get it done” came about before the availability of affordable (Dylos) particle counters. The annoying thing with fine dust is that there is no way to know whether you are adequately controlling it without measuring it. MrRon’s suggestion about looking at visible dust with a flashlight is useful, but not perfect. (Matthias Wandel has some interesting blog posts about trying to quantify that sort of measurement.)

So anyway, imagine you’re Bill Pentz and you really care about this and want people to get it right, but you realize that it’s not feasible for them to close the loop on the control system and actually measure what they’re doing.

The next best thing is to come up with set of very specific, overengineered recommendations that you know from your own experience will work, even if in any particular case you could get the job done in other ways.

I’m sure there’s lots of ways to skin the cat, and given that I have the means of checking whether the cat has been skinned, I may try some ways other than Pentz’s, but I don’t think that to explain why he is so specific in the methods he advocates you have to assume a financial interest.

View MrRon's profile


4710 posts in 3207 days

#10 posted 05-01-2013 09:02 PM

There are air swirl patterns in a shop that will never effectively catch all airborne dust. If you are looking for a “clean room” environment, you will never get it with a shop DC system of any kind.

View John Ormsby's profile

John Ormsby

1283 posts in 3700 days

#11 posted 05-01-2013 09:20 PM

What you don’t seem to understand about Bill Pentz is that he developed the small shop Clearvue size and style of dust collection system. He originally sold full size patterns and then metal kits. He teamed up with the original owner of Clearvue who came up with the idea of using clear Lexan. What happened is the other dust collection makers basically Stole his design and started selling them as their own. You need to know the history of Bill Pentz before you make these types of statements. These are designed for the small shop and hobbyist so they could have an affordable and much safer dust collection system rather than using the old and obsolete dust bag type collectors.
As far as being able to direct vent versus a filter goes. It is always better to direct vent. The problem you are having is your heat ducts and water heater must have normal air pressure. You will need to just block off the heat ducts and the water heater might need to be relocated in order for it to be safe. Or install a completely sealed exhaust vent.It depends on the type of water heater you have as to what can be done with it.

-- Oldworld, Fair Oaks, Ca

View HorizontalMike's profile


7749 posts in 2877 days

#12 posted 05-01-2013 09:53 PM

Good for Pentz and his cyclone, however I chose to build a DIY Phil Thien separator for less than $40, if I remember correctly. It works great and looks ugly, but so what because mine is 30x cheaper and still does NOT pollute the environment.

There are many ways to enhance your DC and I disagree that venting to the outside world is a “good” way to do it. To me, that is no better than walking your dog so your dog will crap in your neighbor’s yard. So you (the proverbial you) want to pollute your local environment and the local kids playing outside get to inhale your dust, or maybe your wife and your kids get to inhale your dust. To me, this is not being responsible.

My opinion, PUT A FILTER ON IT.

-- HorizontalMike -- "Woodpeckers understand..."

View Dusty56's profile


11819 posts in 3651 days

#13 posted 05-01-2013 10:32 PM

As a fellow asthmatic , I have to agree with HMike’s statement about polluting your neighbors air quality.
Seems kind of selfish to dump your waste into the air for others to suffer with. Think about how you would feel if you found out one of your neighbors was doing something that affected your health , but benefited his /hers. Example : your neighbor burns wood in his /her wood stove / fireplace and never opens the damper enough for good combustion and you get to breath in all of the smoldering exhaust that comes into your yard from their chimney. They’re all nice and warm while you’re huffing on your inhaler or heading for the Emergency Room trying to breath.
Just sayin’ , think about it ; )

-- I'm absolutely positive that I couldn't be more uncertain!

View firefighterontheside's profile


17931 posts in 1820 days

#14 posted 05-01-2013 11:30 PM

As a firefighter we never recommend CO detectors in the area of gas appliances because these appliances are always going to give off some CO and will eventually set off your detector. We recommend CO detectors in the living and sleeping areas, hallways and living rooms. It’s while sleeping that CO is the worst as it is odorless. Correct placement for the detector is around 4 feet off the floor. If you have those appliances in your garage, I would say if you’re going to vent to the outside that you need to create some vent such as a cracked door or actual installed louvre. The biggest causes for elevated CO in homes is newer home that are sealed so well that there is negative pressure in the home which causes appliance vents to reverse flow. So I would make sure that you have CO alarms in the home not only because of your shop situation, but also for the fact that you have an attached garage and have gas appliances.

-- Bill M. "People change, walnut doesn't" by Gene.

View John Ormsby's profile

John Ormsby

1283 posts in 3700 days

#15 posted 05-02-2013 12:54 AM

The exhaust air that goes to the open air or filters has a very small percentage of dust with it. The vacuum design of the system actually sucks the dust into the dust bin/can/ So, the filters are just the finally down end exit of the air which is not that bad. The filter is used mainly in enclosed environments where one needs to have a closed shop. That is all.

-- Oldworld, Fair Oaks, Ca

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