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Discussion Starter · #1 ·
Hey, so I am shopping dust collectors, and I started putting together a spreadsheet to compare the published specifications of several units. I thought this would help bring clarity, but the filter ratings don't completely make sense to me.

I don't want to introduce any bias based on brand, so here are the published ratings all by themselves:

filter 1: Merv 15 and 99.999% @ 0.5 microns
filter 2: Merv 16+/- and 99.97 @ 0.3 microns
filter 3: Merv 13 and 99.9% @ 0.2-2 microns

Is it possible to draw any meaningful conclusion from these specifications? The MERV rating and filter efficiency do not seem to correlate!

Based on the filter efficiency numbers, I could be convinced they are the same filter! (But they are not the same filter...)

What do you think? My assumption is the filter rated down to 0.2 microns is the most efficient filter, but the MERV number is actually the lowest. So is it the best filter here, or the worst? Which rating should I pay attention to?
 

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I wouldn't believe any of the numbers. The MERV is way too high to make any sense in a woodworking shop you wouldn't be able to push any air through something as high as 15. Also, the percentage and micron size do not make sense. It sounds like they are using the same smoke and mirrors that they use on horsepower for shop vacs. Don't overthink things. Get the one with the best customer ratings that will meet your needs. Also consider how loud it is. I would suggest that you stay away from Grizzly and Harbor Freight and don't buy more than you really need. Bigger is not always better.
 

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Discussion Starter · #3 ·
I wouldn't believe any of the numbers. The MERV is way too high to make any sense in a woodworking shop you wouldn't be able to push any air through something as high as 15. Also, the percentage and micron size do not make sense. It sounds like they are using the same smoke and mirrors that they use on horsepower for shop vacs. Don't overthink things. Get the one with the best customer ratings that will meet your needs. Also consider how loud it is. I would suggest that you stay away from Grizzly and Harbor Freight and don't buy more than you really need. Bigger is not always better.
Yeah, so part of my goal in posting is to find out who is knowledgeable and who I should listen to in this forum. And this should be important to woodwokers! Right? I mean, I've met people who have been crippled by lung damage--it's tragic. And there are plenty of people sharing their cautionary tales. So the classic, "It's too hard to figure out, so let's just roll the dice." approach is not acceptable to me. (Also, the "Bill Pentz said dust collectors don't work, so only trust Bill Pentz" is another trap to be avoided!)

And I want to point out that HEPA is 99.97% of 0.3 microns and larger, and HEPA dust collectors do very much exist!

The part that doesn't match up is the MERV score of the third filter. I am starting to understand what the score means--it describes the size particles the filter is intended to capture. The higher MERV says that the filter is intended to capture smaller particles.

Apparently MERV 17 = HEPA. Filter 2 claims to be HEPA, but the MERV is 16 +/-, indicating it is just close to being HEPA.

And Filter 3? It seems that a manufacturer is free to assign a MERV rating, but usually they inflate their ratings. I don't understand why they would choose a lower score than what their other data would indicate.
 

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If you look at the numbers for #3 they might be giving you a more honest but still dishonest rating. They say from .02-2 microns. While the others are all well under 1 micron. The other question is how are they achieving such high ratings? What is the cost in doing so. Do they have disposable HEPA filters? If so how much do those filters cost? Sawdust doesn't require HEPA filtration and a HEPA filter will clog pretty fast and become less effective if it's overloaded. Once it starts to clog then all it will be doing is filtering out the larger particles as in choice #3. One thing I have noticed is that once a filter starts to clog up with the fine dust the dust itself seems to filter out more dust. Although that comes with a loss of efficiency.
 

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Discussion Starter · #5 ·
If you look at the numbers for #3 they might be giving you a more honest but still dishonest rating. They say from .02-2 microns. While the others are all well under 1 micron. The other question is how are they achieving such high ratings? What is the cost in doing so. Do they have disposable HEPA filters? If so how much do those filters cost? Sawdust doesn't require HEPA filtration and a HEPA filter will clog pretty fast and become less effective if it's overloaded. Once it starts to clog then all it will be doing is filtering out the larger particles as in choice #3. One thing I have noticed is that once a filter starts to clog up with the fine dust the dust itself seems to filter out more dust. Although that comes with a loss of efficiency.
Your last comment hints at what is going on, as I have learned since originally posting.

However, I have reasons to disagree with your statement, "Sawdust doesn't require HEPA filtration." Your lungs need the fine dust to be removed from the air you are breathing, otherwise some of them will get stuck in your lungs and lead to a reduction of your lung capacity. It is an inevitable, but slow, process. Wood dust isn't "safe" to breathe. (Apparently some woods contain toxins that create an additional danger separate and apart from the problem of fibers getting trapped in your lungs.)
 

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Discussion Starter · #6 ·
Ok, so I guess it is time for the big reveal. I think I found the answer I was looking for.

First off, the numbers I quoted were from (1) ClearVue EF5, (2) Oneida 5hp Dust Gorilla, and (3) Oneida 5hp High Vacuum Cyclone.

I am told the reason the #3 filter has 2 different ratings is because the MERV is measured with a brand new, never used filter, while the other rating is based on a "seasoned" filter in operation.

Apparently HEPA filters are special in that they are designed specifically so there is no "seasoning" required to achieve the max performance.

I don't know much about this seasoning, so if someone knows, please do explain. I was told that it happens quickly, like within the first 20 min of use. And of course "seasoning" is not to be confused with getting covered with "cake" or plugged up with chips. I understand that seasoning remains even after cleaning the filter.
 

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HEPA filtration can never be achieved in a working woodshop with a dust collector. In order to capture 100% (and even that is questionable) of the dust you would have to negative air machine or air scrubber. Aim for 1 micron with a dust collection and you'll be fine.
 

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Discussion Starter · #8 ·
HEPA filtration can never be achieved in a working woodshop with a dust collector. In order to capture 100% (and even that is questionable) of the dust you would have to negative air machine or air scrubber. Aim for 1 micron with a dust collection and you'll be fine.
Hey, I get it. You think HEPA is a hoax or something? I guess that's fine, but that doesn't make it true.

You seem to be confused about the job of the HEPA filter.

The "Aim for 1 micron," advice is bad advice in the sense that you are recommending a machine that will actually fill the air with the small particles that pose the greatest risk. Sure, lots of people follow that advice; hey, everyone here seems infatuated with the harbor freight dust blower thing! But that machine being popular just shows that people are cheap.

The whole point of a HEPA filter is to guarantee the air coming out of the filter is no more dangerous to breath than the ambient air. If you run one of those machines, you should also wear a quality respirator with appropriate filters.

HEPA doesn't make air 100% pure, because that really doesn't exist. It just means that it isn't actively making things worse.
 

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HEPA filtration is needed when what you are dealing with is extremely dangerous. This would include asbestos (which I am certified to remove) or mold spores. But I think you misunderstood what I meant when I said that it couldn't be achieved in a woodworking shop. In order to capture dust particles of less than 1 micron, your shop would have to be treated as an asbestos abatement area. You would need at the least an air scrubber or better yet a negative air system. No matter how good a shop dust collection is it is only as good as the equipment that it is hooked up to. The worst offender in a shop is the table saw. No matter what you do dust is going to get out of it. Don't forget that 1 micron is invisible to the human eye. If you do any sanding forget about the dust collector. If you use a planner or jointer then chips are the biggest issue and you could capture them with a screen door. Yes, there is also dust created, but again the spinning blade puts a lot of that dust in the air. You can see this dust as it settles back onto your workbench and saw top. To get a really good idea after you have installed a dust collection system would be to buy an air handler and hang it from the ceiling. Leave it turned on for at least half an hour after you finish up. At the end of the month check your filter. If it's clean then your dust collection is doing what it was advertised to do. If you have dust in the filter and you're still convinced that your system is better than one that filters out 1 micron then the advertising company has done its job.
 
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