Shop Air Filtration #1: Media Filters

Great job/post Bob, thanks!!!

All woodworkers should take heed to Bob’s advice here.

If not you may end up with COPD (Chronic Obstructive Pulmonary Disease) as outlined in my blog: http://lumberjocks.com/topics/5872

-- Only the Shadow knows....................

I really appreciate this post and you seem to know quite a bit about this. As such, I’m going to ask you a question (hope you don’t mind). I’ve never heard of HEPA filters used for woodworking applications. I ussually hear about these in relatively clean environments where the purpose is to get the air in a clean place even cleaner.

Alternatively, in a woodshop, the objective seems to be to use this more like a vacuum cleaner for the air (make a mess and then suck it up). Won’t a hep filter get overwhelmed much quicker? Maybe thats the point, but I’d like to understand this better. I’m just thinking that if a filter pulls out more dust, there will be more dust on the filter, and it will clog faster.

Before you think I’m trying to make an argument that more dust should be allowed to pass thrhough the filter and get into our lungs, just so we don’t have to change filters as much, let me make it clear that isn’t what I’m saying. I’m just trying to understand the practicality of using the machines, similar to the ones in your link, for this purpose. I didn’t see any (I might have missed them) that look like they are intended to work in shop environments.

Finally, I just want to say thanks again for the post. I’m trying to get up the learning curve on this stuff and am actually putting new tools on hold until I can get comfortable with my air cleaning equipment (although I’m still working in the meantime). I’ll keep reading if you get a chance to post more!

Also, you asked what the efficiency of the filter/box fan results are. According to the filtrete FAQ, it looks like it is capapble of catching down to .3 microns if you get the right one. That being said, they don’t talk about the percentage of .3 micron particles they will grab (which I can see is important). Also, I have no way to know how efficiently my setup recirculates the air.

Thanks Bob 42 for the detailed information re filtration.
I have been interested in this aspect of wood working for some time and would like to offer the folllowing observations:
- The woodshop is self loading.
By that I mean that dust is being continously generated in the enclosed area.
It either settles or is picked up by various suction devices or remains ambient in the air.

The most effective way to reduce the fine particles ( ambients) is to leave a fine filter running during off hours of operation and to replace the primary filter frequently.

I use spun polyester cloth from the sewing center as a filter on my own systems . It is very similar to the material they make disposable facemasks from and is very cheap purchsed this way.

As the dust settles on the material the filter clogs up and finer particles are then trapped..
It’s simple matter of stopping the fan and folding up the polyester and tossing it in the garbage, dust and all.
This currently cost me about 25 cents a change.

I applaude the hepa style filters but they soon become overwhelmed when used in the woodshop making them an expensive investment that potentially prevents ambients from being picked up after they clog up.

-- A mind, like a home, is furnished by its owner

thanx for sharing, it’s one of those things in woodworking that is not too obvious, and does not produce any finished products (you could argue that…) but should be thought of as one of the most important aspects of working in a woodshop… easy to neglect, but a necessity none the less.

-- When in doubt - There is no doubt - Go the safer route.

Thanks to all for responding. These are exactly the questions I was looking for.
HokieMojo – First, I don’t mind at all that’s why I posted this. Second, You are correct about them being used in clean rooms and other types but they are being used in homes that are built very tight along with including outside air, as well as industrial such as lead and asbestos removal things of that nature. When looking for a HEPA unit for a shop you should get one that also has a prefilter. That is what will capture the large particles and the HEPA will take care of the smaller ones. One thing to remember is that the dirtier a HEPA gets the more effective it becomes until it reaches the saturation point and then needs to be replaced. Most good units will have a filter gauge on it to tell you when it’s time to change. The other thing is to try to capture the dust before it goes into the air. That’s were a dust collector and good HEPA vac comes in. The point is not to make the mess and then clean it up, it’s capture it first then your air filter and lungs will be more efficient. Any of those units in my link can be used it a shop and can be altered if you desire. They do mention stand alone units. that’s what you would use. They do have a model 350 that would be great for a small shop and is rated after the filters.
And yes you noticed they didn’t tell you what the percentage is on the filtrete. As far as the air exchanges you need to know the cfm rating of the unit and is it rated before or after the filters. and cu. ft. of the room.

Bob2 – Yes it is good to leave the filter on after you leave the room. Some fine particles can stay airborne for hours even though you don’t see them. Those are the most dangerous to us. The most effective way to control contaminates is how I just explained. Capture as much as possible at the point of source than have the air filter to capture the rest. Then you won’t have to change the filter as much. If you had a particle tester to test the system you are using, you would be very surprised at your results. With all do respect remember the old phrase you get what you pay for, 25 cents worth of filter for 25 cents worth of filtration. I would not suggest a HEPA filter if you do not have any type of dust collection. Then, yes it would clog very fast but that’s what I’m trying to get across. The need to capture at the source and filter.
I hope that helps.

-- Bob K. East Northport, NY

great post bob. allot of great imformation. i am one to never wear a mask. “NEVER”. you name it. exotic woods, plywood, mdf. i was more concerned about urea formaldahyde resin in mdf then small wood particles. after reading your post and realizing how small these particles are and the damage that they can cause made me think twice about getting a filtration system and or wearing a mask “sometimes”. lol

my real question for you bob is more about the filter for my home heating and air conditioning unit. my Heater and A/C for the house is located in my shop just behind my lathe and workbench. there is no wall seperating the unit. all airborne dust particles build up on the unit itself. i remove and clean the filter regularly. maybey once a month. i think the filter is made of some tybe of carbon sandwitched beetween two nets and a metal gate. whener i hose it down large amounts of dark dusty water wash down the driveway. my question is what kind of filter do you think that is, and is it catching the majority if not all the dust that enters the duct pipes leading to the house. is there a better filter i can get. how should i clean it. and how often. or do you think a shop filtration system would eliminate most of the dust from entering the A/C filter all together. seeing how educated your are on filtration i thought you would know something about other filltration devices such as the one for my A/C. let me know what you think. THANKS

-- i can do all things through christ who strengthens me

I think where you and I might see things differently Bob is with the amount or shop time we each have and perhaps the exposure to the real world of woodworking.
I don’t mean to be insulting but my experience suggests that the production and control of dust particles in a practical surrounding is far different than in a class room or a book.
I pretty much agree with all you have mentioned above.

But… as I said it’s often just not practicle. ( a goal to strive for yes).
I think you will find that sanding is one of the worst dust producers followed closely with bandsawing and for blowback I give a prize to the 12” CMS.
Somewhere I have labs test that show without doubt the overhead dust filters actually can create currents of microscopic particles that simply “circulate” in the air as long as the filters operate.
Unfortunately that would apply to filters using Hepa technology as well.

I am not certain that you are familair with the spun polyester material that I am refering to as you dismissed it as not being adequate because of the price.
”you get what you pay for, 25 cents worth of filter for 25 cents worth of filtration”

I urge you to try some in your own environment before you judge it as not acceptable.

http://lumberjocks.com/topics/3888

Cheers

Bob

-- A mind, like a home, is furnished by its owner

Good Comments by Bob on understanding the workings of air filters. I too am part of the air filtration industry having worked for 25 years in the business and now Executive Diretor of the National Air Filtration Association (NAFA), trade group for air filter manufacturers and distributors, worldwide. In regards to the followup question about HEPA filters in a woodworking shop, the answer is how clean do you want your air? Since most wood shops are not air tight enclosures, like a cleanroom, you probably want the air cleaned of any lung-damaging particles – those in the <2.5 micrometer range. HEPA filters would be a bit over the top and a standard MERV 14/15 filter, like those found in the commercial units (with a MERV 6-8 prefilter) mentioned in a previous emails, will remove most all of this size of particle and are affordable. I would echo the sentiments expressed by a previous blog that airflow through the unit and air changes in the shop are the key to cleaning the air. The formula is l x w x h to get cubic feet of your shop, then find out cubic feet per minute (cfm) of air cleaned times 60 – divide and find out how many air changes per hour the unit provides.
AL

-- Alan C. Veeck

Welcome to LJ’s Alan.
I look forward to seeing your shop and some of your projects in the not too distant future.
Interesting perspective that you birng to the discussion.

Perhaps from your experience, you can recall just how much ambient “detritus” would be considered normal in normal air in most urban cities today?

It would be interesting to gauge that against a moderately “scrubbed” wood shop.

In Canada for instance the Govt is no longer recommending forced air furnace cleaning as an annual routine stating that normal dust in the air will almost immediately replace anything removed by the commercial vacuum trucks.

Bob

-- A mind, like a home, is furnished by its owner

Bob #2, No insult taken or meant to be given. It’s OK to disagree. That’s what makes us different. I have a wife and with that comes with a tough skin. ;-)
I am one that likes to keep a clean shop even when working. I will stop sometimes to clean up and then continue. A HEPA filter is still the best choice but consideration must be taken when making the choice of how clean do you want it and do you have a need. Such as someone with allergies or respiratory problems. If a HEPA filter is going to keep them in the shop then that’s the choice they have to make. My point again is to capture the contaminates as much as possible at the source and then you can have a better air cleaner that won’t dirty up as fast and you will be healthier in the long run.
Thanks for giving me the info on your filter material I will check it out. I do try to keep an open mind. As far as the tests that show air filters keep particles in the air as long as they are on, depends on the size particle and how strong is the filter unit is.

I have a HEPA unit installed in my central AC in a by pass configuration. It has been in for 17 years and when I check the duct work from time to time it is spotless. Along with the coils, I mean you could eat off it. No need to clean the duct work. It runs all year to filter the house.

Alan Veeck, Welcome to LJ’s.
Glad to see you jump in. As I said it depends on how much you have a need.

Mike Shea, I would be concerned that you are sucking in contaminates from the shop through the gaps in the duct work as well the filter. It’s hard to know what you have and I’m not here to try to fix it but, I would start by sealing up any leaks in the duct work such as where they join. and think about a partition wall to keep it separate from the shop. Check the duct work. That will tell you how good your air filter is.

That’s my opinion. :-)

-- Bob K. East Northport, NY

Good Morning Bob in Canada…RE; your question about “detritus” in outdoor air versus the typical shop. While detritus leans more to organic matter in the air, there really are no difinitive data on this that I have seen. Particle counts in outdoor air vary from place to place but normally run from 1 million to 3 million paricles per cubic foot of air. Most of these are in the smaller diameter range. Indoors, 1-2 million would be high…for themost part I have seen in 300,000 to 500,000 range fairly standard.
If you run an air cleaner in an area with a MERV 14 or 15 filter and you are not adding more particles, you can clean it to under 50,000. Remember, your nose does a good job on those bigger particles…the ones >10 micrometers an above and your upper respiratory system helps clean down to about 5 micrometers. It is believed that very small particles, those <0.5 micrometers may very well go in and come back out depending on their composition.
Bottom line is cleaning the air of fine and ultrafine particles – those in the 2.5 to .5 micrometer range is healthy since your body does not have to remove these from your lungs.
AL

-- Alan C. Veeck

Hi Al:
Those stats are similar to what I have been seeing over the last 10 years or so here too.
Electrostatic filters are still pretty prevalent here and recommended by HVAC vendors for forced air furnace systems. They are not practical for wood shops as they load very quickly in the environment and take a period of time to be reconstituted for reuse.

In my own shop I use a 2 hp cyclone system with a gate at each stationery machine. (1 micron felt bag)

I use a portable vacuum with an automatic switch for hand held tools like sanders and routers.

For lathe work I use a filtered positive pressure helmet for protection.

I have an overhead ambient filter with 2 furnace filters to catch the large particles and a layer of spun polyester film to handle the fines.
At the end of each shift in the shop I “pressure wash” the surfaces with compressed air and leave the filters running for a couple of hours after I leave the area, ( I wear my dust filter helmet during this procedure)
My shop will pass the white glove test when I return the next day to work.

That’s about the best I feel I can do and still have some shop time.

Bob

-- A mind, like a home, is furnished by its owner

Bob#2
From what you have described to Alan you seen to be taking a lot of good precautions. I wish more did the same.

-- Bob K. East Northport, NY

Thank you very much for all of the information. I am pretty new to woodworking and want to make sure my dust collection is decent – no health issues needed here. I’m thinking of buying the Jet DC-1100CK http://www.cpojettools.com/products/708636ck.html
You mention that one key to dust collection is to get it at the source? Will the Jet I mention above do a good job of that? Will it be better than my shop vac?
Also, will it be able to collect well from my Router and ROS if I get a smaller hose attachment.

-- "Whether you think you can, or whether you think you can't, you're right."

extremely useful post.. thanks

-- making sawdust....

Snoop, The 1 micron filter is even better than the 2 micron if cost is not a factor. You said no health issues and that’s a blessing, but the cleaner you keep the air now will hopefully keep you that way. It sounds like you are headed in the right direction. This will be a significant increase from the shop vac. Assuming that the vac is not HEPA. It still wouldn’t have the power of the dust collector. How good any dust collection works depends on if it is sized and duct work installed properly. As far as connecting to your router and ROS depends on the sizes. You can find many adapters online such as Rockler. This will keep the shop cleaner but you should also think about an air cleaner for the future to collect the smaller particles that will stay floating for hours. Those are the most damaging to us. I hope this was helpful.

-- Bob K. East Northport, NY

That was very helpful. Thank you for all of the information. Sounds like I may have a decision to make between my shop vac with Hepa and the Jet dust collector. The information you provide above is very useful and I appreciate it.

-- "Whether you think you can, or whether you think you can't, you're right."

snoop, You might be able to upgrade the filter in the shop vac with a HEPA, check with the manufacturer.

-- Bob K. East Northport, NY

I’ve been looking around at various air filtration recommendations, based on CFM ratings, filters, prefilters, etc… One thing I haven’t found is an upper rating for CFM for filtration systems. Is there any general rule of thumb for an upper bound? Something along the lines of “Don’t go over X times your minimum CFM rating.”

In a world where bigger and more powerful usually means better, I don’t want to accidentally go overboard and create a tornado in the shop.

Bob42,
I have the Craftsman 17762 model from Sears (http://www.sears.com/shc/s/p_10153_12605_00917762000P).
I am able to upgrade to a HEPA filter with this vac, but as you mentioned earlier a lot depends on the percentage of material captured at 0.3 micron level. I did some searching but couldn’t find any info on percentages for the HEPA filter…do you happen to know of a resource I could reference for this? As you can tell by all my questions capturing as much of the fine dust as possible is really important to me.
Regardless of whether I end up with the HEPA filter on the vac or the dust collection I think your info has convinced me that an air filtration system is really necessary, so that suddenly went to the top of my list for next shop purchases. I actually found a really great deal for a used one online – it is the Jet AFS-1500 for only $150…seems like a really good deal to me so I think I may go ahead and get it. If anyone has this particular model I would be curious to hear thoughts (didn’t see any reviews for this on lumberjocks yet).

-- "Whether you think you can, or whether you think you can't, you're right."

Snoop, That seems to me to be a good price to me. If you don’t have any health problems to date that would restrict you then that looks like a decent filter. Most shops are not going to use a HEPA filter unless you really have a need, but the cleaner you keep it the better you will be in the long term. I like the dust collector because it’s more powerful than the vac on the bigger machines. Then use the shop vac for the little stuff. As far as HEPA goes, the closer you get to a rating of 99.97% at 0.3 microns the better the filter. 95% at 1 micron is less efficient but good for most shops.

Rogue42, You have to size the filter (cfm) to the size of the room (cu. ft.) to determine how many air changes per hour you need. You do not want a tornado effect but enough to circulate to capture the particles. A filter unit with variable speeds works well because when you want to clean the room fast you can but also slow it down so you don’t just push it around the room. The general rule is about 4-6 air changes per hour for good circulation and 1-2 for maintaining over a longer period. I like to turn it down or off before I start finishing. Your right, bigger is not better in this case. Always keep in mind these are general rules and you must look at you particular needs.

-- Bob K. East Northport, NY

Thanks, that’s pretty much what I had figured. I knew about the 4-6 changes/hour figure, but wanted to clarify that changing it upwards of 20x an hour would be bad. (If not a bit breezy!)

Snoop, I think we might have been looking at the same AFS-1500 unit… 8-)

Roque42,
Yes, 20 X would over kill and make more of a mess.

-- Bob K. East Northport, NY

I want to make a correction on my first post.
In the fourth paragraph after filter ratings it starts off by saying:

When choosing a filter of any type remember that the more air changes per hour the more you will filter. One question to ask: Is the cfm of the unit rated before the filters are installed or after? If they can’t tell you then you must assume that is is rated after. That will effect the cfm of the unit dramatically if it is rated before and puts a strain on the motor.

Correction! It should read:

When choosing a filter of any type remember that the more air changes per hour the more you will filter. One question to ask: Is the cfm of the unit rated before the filters are installed or after? If they can’t tell you then you must assume that is is rated before the filters are installed. That will effect the cfm of the unit dramatically if it is rated before and puts a strain on the motor.

I am very sorry if that messed any one up. Please accept my apology. I proof read it but must have over look it.

I am working on getting time to write a little something soon on ERV’s (energy recovering ventilators) and the possible use in the shop.

-- Bob K. East Northport, NY

Thanks Bob42 for all of the information! I may end up going with the shop vac with HEPA filter since it sounds like that may get more of the fine dust.

Rogue42, I went ahead and purchased the jet air filtration. don’t have it installed yet but when i do i’ll let you know how it goes.

-- "Whether you think you can, or whether you think you can't, you're right."

Thank-you all for the great info.

Bob42 I am thrilled to be able to learn from you. I now better understand dust collection, though I have always been as cautious as I could be based on what I knew. In approx 2 months I will be leasing a 24.5×50 x 16 ceilings shop and will have all the basic tools of a well equipped do-it-yourself shop. 2 table saws, oscilating belt sander, 24” panel sander, 20” planer, a shaper, 8” joiner, 19” bandsaw, chopsaw, router, & lathe are the major dust makers. I was planning on three 1321cfm stand alones with 2 micron bags. I am now considering an air purifier since I have been learning. First of all how do I know how many machines I can use at once with each stand-alone? Do I have enough or not enough stand-alones for collecting at the source? And am I thinking about hooking this up completely wrong or not? I’d spend $4000 if I had too.

Also I am building a small paint bay 10’ x 10’ vented outside through the wall. I’ll be using industrial lacquers and such. Where do I start? Suggestions from anyone will be much appreciated.

-- "Safe woodworking isn't just about avoiding injury, it is also about avoiding extinction." CKG

Hey Bob.. when is a part II coming? ;)

-- Martin, http://lumberjocks.com | My Facebook: http://profile.to/msojka

Cameron, Look at www.billpentz.com, his site will give you the calculations on how to determine your dust collector and ducting. If you can get down to the 1 micron canister would be better. You need to calculate how much power you have to run multiple machines and the proper ducting. If you are using them as a stand alone you will be taking alot of time moving from machine to machine. You might think about one large dust collector maybe a cyclone, and the proper ducting. In the long run it would save you time, and time is money.

In the paint room you have to be very careful with fumes.
If you are doing alot of finishing you should go with an explosion proof motor. That is a good place for a energy recovery ventilator. That will exchange the air in the room but not send you heat or AC out the window.I’ll post that soon. I hope that helps.

Martin,
I have been working on a renovation in my house and taking my father to Dr appointments. Sorry for the delay in part II. I will get it up next week.

-- Bob K. East Northport, NY

Great post on filtration…...... now I am totally confused….............LOL Just kidding.

-- Jerry--A man can never have enough tools or clamps

I’m thinking of upgrading from the supplied bag on the Jet DC to a 1 micron bag Will that adversely affect the amount of draw on the system (because it will provide smaller holes for the air to return to the shop)?

Lee

-- No piece is cut too short. It was meant for a smaller project.

Sawdust2,
Your thinking is correct, but many of us have done the upgrade and had no problem. It will make the motor work harder and it would be wise to call Jet and see what they say before you do it. You should see a cleaner shop if you do it.

-- Bob K. East Northport, NY

Ok.. coal miners used to take a canary down into the mines. The canary was very sensitive to poisons and would die giving the miners a warning that something was wrong; or so I’m told.

Anyway, We have a canary too. Do a day of woodworking.. Really cut it up and do some sanding. Later that evening (I know this is disgusting) Blow your nose. Everyone here, I’ll bet, knows what I mean. Our noses catch dust but not the fine stuff. How’s yours?

Strange post huh?

-- The smell of wood, coffee in the cup, the wife let's me do my thing, the lake is peaceful. http://web.me.com/deceiver6/Deceiver/Craftsman_on_the_lake/Craftsman_on_the_lake.html

Thanks for all of the info. Lots to chew upon. (Sorry for the pun)

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †

Daniel,

You hit it right on the nose! (I couldn’t help that). Over time that can do damage.

Thanks to all for your responses.

-- Bob K. East Northport, NY