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Workshop Air Filtration System Performance Shootout - Including Effective, Low-Cost DIY Box Fan Filtration Systems

6/28/2019

28 Comments

 
Copyright 2019, Shop Hacks, all rights reserved
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Dust is like a bully… you don’t know how to avoid him so you just give him your lunch money.  Then one day you learn how defend yourself.  Once you learn how to beat the bully, you are free and you never have to be bothered by him again…  

Do you enjoy cleaning, wearing and breathing dust in your home or workshop?  This is the first in a series of articles that will empower you with the knowledge you need to beat dust in your workshop without spending a fortune on dust collection and air filtration systems. 
​
We tested 8 different  air filtration systems to determine which ones worked best and how you can can have cleaner air in your home or workshop without spending a small fortune.  We tested and compared several commercial air cleaners, a household HEPA air filtration system and several DIY air filtration solutions including a super cheap and simple box fan with a furnace filter.  We used a laser particle counter  to measure dust removal and air filtration performance so you can have confidence that the results presented in this article are objective and reliable.    You  no longer have to rely on Internet opinions.

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I am not sponsored or compensated   by any company  so you can rest assured that all of the results in this test  are unbiased.  I spent several hundred dollars of my own  money and a week and a half of my time to bring this to we can all see which systems may work best for your shop.  My hope is that many of you will use this information to build an even better filtration system and then share it with the community.  I hope the information presented in this article empowers you to create your own air filtration system.  Shop Hacks exists to help you Build Your Space and clean, healthy air is certainly a foundational component of getting the most out of your shop time!

I encourage you to interact in the comments section of this blog and to share the link with friend  and groups that may benefit from this information.  Link to this article HERE.
Is dust really a problem?
That's a great question that doesn't get much attention.   Everyone knows an old-timer who brags about breathing 10 gallons of dust a day for 30 years without a problem.  So, is dust really a problem or is it just something that  we can ignore so we can focus on getting  projects out the door?

Let's start with   a couple obvious benefits of having a nearly dust free workshop...

​1.  You will   spend more time making, building and fixing and less time cleaning  if you capture the dust before it settles on your tools and floor. 

​Did you enjoy cleaning your room when you were a kid?  We all know the answer to that question.  Then why do you not mind having to clean up your shop after every project?  I spent 3 hours cleaning all the dust off of everything after this test.  If I would have used my dust collection and air filtration systems there wouldn't  have been any dust to clean up at all and I would have spent those 3 hours working on something I enjoy.
 

​With effective dust collection and air filtration you will spend more time making, building and fixing and  MUCH less time cleaning.
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2.  Using open tool storage  can save hundreds of hours per year if you work in your shop every day.  

​If you can capture the dust before it lands on your tools and materials you can use open tool storage which is much more time efficient than storing tools in boxes or  cabinets.  
 
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​Open tool storage requires no secondary operations to use a tool  and can save hundreds of hours over the course of just one year.    
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 You don't have to look for tools, you can grab them and put them back without having to open a drawer or  door.  However,  if you don't have good dust collection open tool storage isn't feasible because dust would cover them in no time.  However, if you modify your tool dust ports and install an effective air filtration system then you won't have to worry about dust on anything.  I've had the open storage system shown in the picture above for over 2 years now and I never have to clean any dust off.  It is a joy to be able to reach for and put away most of the tools I use every day without having to walk to a cabinet or open a door or drawer.  ​
3.  Dust is an invisible enemy to your long-term health. 

The dust that does the most damage in your body is the dust that you can't even see.    You can see  dust particles as small as   100 microns.  Dust that is 100 microns or larger is very likely to get trapped in your nose, throat or upper respiratory system and  coughed back out so it doesn't pose as much risk as the very fine particles.   However, larger particles can still lead to allergies or  nasal cancer due to  the chemicals that are in wood products.   Dust from some exotic wood species also expose you to a higher risk for allergies and nasal cancer.  You can find a table listing the relative toxicity of different wood species HERE.
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Image from ​   https://www.epa.gov/pm-pollution/particulate-matter-pm-basics
An even larger problem lies with dust that is so small that you can't see it.  Dust consisting of particles that are  5 microns and smaller can travel the to the full extents of your lungs and enter your bloodstream.  Think about what is in the dust you breathe.  MDF, plywood and treated woods are full of chemicals from glues, binders, formaldehyde, and other chemical agents.    You would never consider allowing someone to inject even trace amounts of these into your blood with a needle but that's essentially what you are doing every time you breath these particles.  They enter the blood which  leads to inflammation which is  at the root of many diseases.

I started taking dust collection and air filtration seriously after leading a NASA research project that studied the effects of recycling plastics in space.  Part of that project included researching the ​ long term effects of airborne particulates  on human health.  That research convinced me to start taking dust collection much more seriously. I didn't want my hobby to negatively impact my long-term health.  I purchased a laser particle counter so I could see the dust that  was previously invisible to me.  Once I could see what tools were the worst offenders and how bad the air quality really was in my shop most of the time, I redesigned the dust ports of the worst offending tools then I worked my way to the rest one by one.  In future articles, I'll show you how to modify your tool dust ports to make them MUCH more effective at capturing dust.  A little hint though, if you can capture the dust before it gets more than 1" away from the source you don't need an expensive dust collection system to do a very effective job.  You can't always capture 100% of the dust so I developed air filtration systems to reduce the time that any dust that  escaped my dust collection systems  stayed in the air.   Those systems are included in the testing performed here.

​Now I enjoy  a nearly dust free shop with air that is typically 10x cleaner than the  air outside the shop.  I now go into    my shop to get a breath of fresh air.  Clean and safe air was my initial goal but saving time and not having to  wear, breathe or clean up the dust were wonderful side benefits that I would never want to do without now that I've become accustomed to them.  I never knew how much I would  come to love being able to make a cut without wearing or breathing any dust.   In the early part of the 20th century people scoffed at the idea of indoor plumbing.   Who needs that in their house?  Once they realized the benefits it was obvious that the old way was outdated.  Some people still have an outdated view regarding dust collection and air filtration.  We are getting close to a major shift in attitudes regarding dust collection in the workshop.  This article should help further the knowledge that can save your health and buy you more time doing what you love to do.
In this article you will learn...
  • How effective are air filtration systems?
  • How can you improve the performance of your air filtration system?
                      (I  improved the Powermatic PM 1200 system performance over 30% with a free, 30 second 
                       modification)
  • Will an air filtration system replace effective dust collection?
  • How much do air filtration systems cost?
  • What features should I look for?
  • What are the benefits to using an air filtration system? 
  • Do air filtration systems really make a noticeable difference?
  • Test results
    • Using scientific testing, how well did each air filtration system perform? 
    • How does a $37 DIY air filtration system measure up to a $500 system? (spoiler alert... surprisingly well)
    • Do the types of filters used make much difference?
    • Does    the location or orientation of the system in your home or workshop matter?
    • Are DIY box fan filtration systems safe?
    • Should I use a furnace blower or an axial fan?
  • How to choose the right size air filtration system for your home or workshop?
  • How much do air filtration systems cost to operate?
  • How do the noise levels of the various air filtrations systems compare?
Air Filtration System Features, Testing, and Results
Air Filtration   System Features
Retail air filtration systems include a couple  features that you may find helpful.

Remote  control:    Remote controls are nice if you want to turn the air filtration system on/off without having to reach it.  I keep my remote next to the door so as I leave the shop I can set a timer to run the air filtration system for a couple hours to clear any remaining dust from the air.  The remotes allow powering on/off, changing air speed and setting the countdown timer. 

There are two types of remotes, 1) radio frequency(RF) and 2) infrared (IR).  RF remotes work even if there is not a clear line of sight between the transmitter and receiver.  Infrared (IR) remotes require a direct line of sight to work so they  will not work if there's anything between the remote and the receiver.   Think of an IR remote as a flashlight.  If you can't hit the receiver with a beam of light from the transmitter  it won't work.   I recommend buying units that come with RF remotes.
​
Timers:   Timers allow you to set the air filtration system to run  1 to 9 hours after you leave the shop.  The WEN unit has settings for 1,2 and 4 hours.  The Powermatic unit allows up to 9 hours.  Timers are handy because you can make your last cut just before leaving your shop then set the air filter to run for a couple of hours to clean the air without having to stick around.    That reduces the fine layer of dust that coats everything.
Systems Tested
Table 1​  summarizes, in no particular order, the systems tested as well as their various performance characteristics and features.  The best  of each category is highlighted in green.
You will also find the results of the following tests summarized in Table 1.  
  • Time to bring particle counts from 1M to 300k (just below the very unhealthy air quality level)
  • Time to bring particle counts from 1M to 30k (to the "good" air quality level)
  • Max power consumption  (Watts)
  • Operating flow rate (CFM)
  • Max static pressure (in-wc)
  • Noise Level (dB 6' away from the outlet)
  • Filtration efficiency (particle concentration in / particle concentration out)
  • Cost to run each system 10 hours/day for one year.
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Table 1 – Air filtration systems specifications and features
​

We also tested and documented the following ...
  • Box fan with a discount brand filter
  • Particle counts over time with dust collection OFF and  Air filtration system OFF
  • Particle counts over time with dust collection ON and Air filtration system OFF
You can find a summary of results in the Test Results Summary section.
Lessons Learned...
  1. A DIY air filtration system can be more effective than an expensive retail system and is capable of making the air in your home or workshop much cleaner than the air outside. 
  2. One or two table saw cuts without effective dust collection can raise workshop dust particle concentrations to well above unhealthy levels.  Without an air filtration system these particles can accumulate to extremely unhealthy concentrations and linger in the air for over 5 hours.
  3. Effective dust collection is the only way to maintain a health work environment.  Air filtration systems reduce the time that unhealthy dust concentrations persist but they are easily overwhelmed    with even a small number of cuts.   Using a good dust collection system is 100x more effective than an air filtration system but both systems should be used.
  4. Having a way to measure dust concentrations in your home or workshop is invaluable if you value your health and want a way to know if what you are doing works or if it    does not work.  I recommend researching some of the new air quality meters on Amazon if you are looking for a lower cost option.  I used the   Dylos DC1100 Pro laser particle counter    for these tests.
  5. In my testing, a low-cost DIY air filtration system outperformed a $500 retail air filtration system as well all other retail systems tested including a HEPA filtration air purifier.
  6. Floor fans create more pressure and more flow than box fans so they work better for this type of application.
  7. It is important to match the filter configuration to the fan being used to maximize efficiency and not waste power or money.  More filter area is always better if you have room for it.
  8. The best air filtration system performed about the same as putting one box fan (no filters)  in a window blowing in and one fan blowing out.
  9. One system that I use with 2-year-old dirty filters still performs relatively well compared to brand new systems.  If you don't heat or cool your workshop you can just use fans with no filters and they will work as well or better.  If you heat or cool your shop then an air filtration system is definitely worth the small investment.
  10. I DO NOT TRUST DISCOUNT OR CHEAP FILTERS.  Under the same test conditions, a   discount filter that was rated as MERV 12  was very ineffective in my tests compared to a 3M filter rated at MERV 11. I won’t use a discount filter or a filter rated less than MERV 11   unless I have a way to verify that it is working to the claimed specifications.  You can not tell just by looking for visible dust in the filter since the dust that affects your health is too small to see.  Some filters are simply placebos and may not  protect you.
  11. Using a separate fan to recirculate air around the shop did not affect the air filtration system efficiency at all.
  12. The size of your workshop affects how air filtration systems perform.  For a large shop, dust concentrations won't go as high but they will take longer to filter to safe levels.
  13. Even with   completely  blocked flow, the motors in the two box fans that I tested only heated up to 80F.  These particular fans  would not overheat due to a completely clogged filter.
  14. The location of your filtration system can have a significant affect on your workshop temperature.   Air near the floor can be as much as 10F cooler than air above your head.  Consider this when you mount your air filtration system so you don't  heat the air during the summer or cool it during the winter.
  15. Aim for enough air flow to achieve 6 air exchanges per hour based on the fan flow rate and the volume of your shop.  However, that rule of thumb doesn’t tell the whole story.  All that really matters is how quickly your system can lower dust concentration levels.
  16. Running 10 hours per day the units tested will cost between $3/month and $10/month in electricity costs.
  17. Contrary to popular belief, most furnace blowers (squirrel cage) use LESS power as the flow is restricted.  (this is true for most types but not all).  If you keep the filter clean it will not harm your furnace blower motor.  If you don't keep it clean it can overheat your furnace blower motor.
Test Results Summary
For those of you who just want the facts without the commentary then Figures 1 and 2 and Table 2 summarize,  at a glance, the performance of all of the systems tested.  You can read about specific nuances of each system and several of the important lessons learned in the Systems Performance Summary section.  You can go straight to the Recommendations section if you don't care to know how it works and just want to get started right away.
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Figure 1   – This Chart Summarizes the Performance of all the Systems Tested
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Figure 2 – Time required to clear the air in a 24’x32’x8’ workshop
(Clear from 1 million particles per cubic foot to 30,000.  Particles > 0.5 microns)
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Table 2 –  Time required to clean the air from
​1M to 30,000 particles/ft3 (particles > 0.5 microns)
>300,000 = "Very Unhealthy"
​  <30,000 = "good" air quality

​

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Click to Build   The Ultimate Flip Top Workbench (Plans and Hardware)
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Shop    Hacks   Recommendations 
Best of test...
This system cleared the air in my 2 1/2 car size workshop to a very healthy dust concentration in just 27 minutes compared to over 40 minutes for the Powermatic PM 1200.    With just one set of the filters recommended below this system will perform even better.  This system has two advantages over a simple single filter box fan system - this fan produces more static pressure and more flow and the 2-filter configuration creates 1/4th as much pressure drop as a 1-filter system.

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Components: $90
Lasko 20" High Velocity Fan 2264QM  (Recommended for dual filter V-configuration setup)
In the test I used MERV 6 and MERV 11 filters stacked .  However, after further research I recommend using  one   3M   Filtrete MPR 1900  20x20x1 filter   on each side      to provide even more airflow AND better filtration efficiency.
​(or one 20x25x1 on each side would be even better)
One caveat to furnace filter and axial fan type systems... for a one or two filter system, the flow rate will decrease faster using an axial fan (box fan) than with a cage (furnace) blower system as the filters load with dust.  This means that you will need to clean the filters regularly to maintain performance or use a 4 filter configuration (each filter handling 1/4th of the airflow) to outperform the squirrel cage blower systems even with dirty filters.  Axial fans deliver 1/10th to 1/5th as much static pressure as cage blowers so you will need at least 3x as much filter area to match a cage blower system performance as the filters start to clog.  A 4-filter system should have approximately 1/16th as much pressure drop for any given flow rate compared to a 1-filter system.

The Shop Hacks Ultimate Air Filtration System uses 5 filters so CFM is maintained even as the filters become caked with dust.
Best compact DIY Box Fan Filtration System
This system is recommended for a compact and hassle-free way to move toward a healthier work environment.  Use one of these for each 2500 cubic feet of workshop volume (15x20x8, 1 car garage).    Two of these units should offer close to or slightly less than the performance of one ($500) Powermatic PM 1200 air filtration system if you keep the filter cleaned out.

The following accessories make it a little easier  but you don't need them if you don't want to use them.   Duct tape works fine also.
​

(optional)   Silicone box fan filter grips  (I used these for the box fan filter tests.  They are recommended if you value simplicity of use over cost)
(optional)    Cardboard magnetic filter holder    (I didn't use this but it may be worth looking at if you you like a more finished look.  It certainly is not required to obtain good performance)


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Components: $48
Pelonis FB50-16HB   Good build quality, front controls.  Not sold on Amazon but the link provided is the same fan distributed by a different company.)

In the test I used MERV 6 and MERV 11 filters stacked .  However, after further research I recommend using a single  
3M Filtrete MPR 1900  20x20x1 filter  (NOT  2 filters as shown in the photo) to provide even more airflow AND better filtration efficiency.

Deep Dive - Continue reading if you are the type that wants to understand more about this topic including how these tests were performed.
Will a clogged filter on a box fan cause a fire?
We might as well discuss this first since it is bound to come up in any discussion.    Are box fan filtration systems a safety hazard?  It is definitely worth asking the question.
We completely sealed the back side of two models of box fans and ran them for 20 minutes with a thermocouple attached to the motor housing.  The motor only warmed a little bit.  Internal circulation in the fan was more than enough to keep the motors cool.

This doesn't mean every model is safe so the only way to be sure is to test your fan.
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You will see many people claim that a box fan will overheat if the filter  becomes clogged. I  put it to the test.  I  placed a thermocouple on the metal motor housing of two different box fan models and COMPLETELY blocked the airflow by duct taping a piece of cardboard completely covering the rear of the fan so that no air could pass.  I ran the fans for 30 minutes which was long enough for them to reach their maximum temperatures.  In each case the motor housings stabilized at around 82F in a shop air temperature of 70F.  ​
Fans create a lot of flow in and out of the front grate even if the rear is blocked.  Apparently, for the two fans I tested, that was enough circulation to keep the motors cool.  The fact that the filter keeps dust from accumulating on the fan motor housing and coils probably offers more protection than danger in most cases.   A box fan filtration system will work with the filter on the front or the  rear.  However, you should mount the filter on the  inlet side to protect the motor and blades from dust and lint accumulation.

While this is not a definitive test by any means, I believe it is enough to calm any fears I have that a clogged filter will cause either of these two fan models to start a fire.  If you are worried you should to run the same test with the model fan that you choose to use.

Conclusion:  I don't believe a clogged filter could start a fire in the two fan models that I tested.  However, that doesn't mean that every fan model is safe or that these fans couldn't change over time so you should assume that your fan can catch fire if you don't keep the  filters clean enough to flow plenty of air unless you test it yourself.    I have heard two first-hand accounts from friends who said that they have had a box fan catch fire or almost catch fire.
​


​Motor temperature rise with the back side of two different fan models ​with    
completely blocked  air flow.
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Filtration Performance Test protocol
Each test consisted of cutting about 12 ft of ½” MDF and 12 ft of ¾” melamine on a table saw with the blade elevated 2” above the stock (to create even more dust).  This raised the dust concentration levels in the shop to over 1,000,000 particles per cubic foot for particles > 0.5 microns.  After the cuts were completed and the particle count reached the limit, the air filtration system was turned on and particle counts were  logged from 1M particles/ft3 (very unhealthy air quality) until the level reached 30,000 particles/ft3 ("good" air quality).  




​We cut several feet of MDF and melamine for each test to bring particle counts over 1 million particles per cubic foot (particles > 0.5 microns).  The air filtration system being tested was turned on and particle counts were logged using a Dylos DC 100 Pro laser particle counter with a computer interface until levels dropped below 30,000 particles per cubic foot which is considered "good" air quality.
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For reference,   according to the laser particle meter manufacturer,  particle counts over 300,000 particles per cubic foot is "Very Poor" air quality.  Particle counts under 30,000 particles per cubic foot are considered "Good " air quality.  The graphs below show how quickly the various systems tested  lower the particle counts over time.  Typical particle counts for the outside air where I live (in the Ohio Valley) average between 50,000 and 100,000 particles per cubic foot for particles > 0.5 microns.  The air quality here is not very good but it is excellent inside my workshop.
​System Sizing Considerations
This is a good place to include this information since the test results presented in this article are affected by the volume of my workshop.  If you run the same test in a smaller shop the particle concentration will go much higher and will drop much faster.  In a larger shop the particle counts won't rise as high and it will take longer to bring them down to safe levels.

​My workshop is 24'x32'x8' 2 1/2 car garage which is 6144 cubic feet.  To determine the  volume of your workshop just multiply the length x width x height.    If you  don't have a flat ceiling then the  volume will be less.     Unfortunately you won't be able to simply compare your shop  volume to mine to determine what size system you need.  The general rule of thumb is to choose a system that will move enough air to pass the full volume of your shop at least 6x per hour.  So, if your shop has 6000 cubic feet of air volume then aim for a unit, or multiple units that can flow at least 600 CFM combined.  (I.E. 6 air exchanges per hour x 6000 cubic feet = 36,000 cubic feet per hour.  Divide that by 60 minutes per hour and you get 600 CFM minimum flow rate target.  However, any air filtration is better than no air filtration  as long as the system uses decent filters.  

REMEMBER... effective dust collection should ALWAYS be a first priority.  No air filtration system can protect you from harmful concentrations of dust unless you have effective dust collection.
An important note about flow and filter ratings and flow rate
When I started the tests for this article I noticed that the MERV 6 filter that I was using as a prefilter had nearly as much pressure drop as the  MERV 11 main filter.  I assumed that a  higher rated filter would  be much more restrictive.  However, I looked into it some more and found several references that  showed that MERV ratings and  flow restriction are not always related.  As  you can see in Figure 3 below, a higher  filter rating doesn't always mean the filter will be more restrictive.  I haven't verified these results myself but they indicate that the Filtrete 1900 filter is superior in both filtration efficiency and flow rate compared to several other filters, including filters with lower MERV ratings.
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Figure 3 – A higher MERV rating doesn't always mean a filter will be more restrictive
As a result of this finding, I  recommend that you use the   Filtrete MPR 1900  20x24x1 filter  or the 20x20x1 size for any filtration system you make yourself.    It provides a slightly higher efficiency an a lower pressure drop that the filters I used in this test.  Using a cheap fiberglass prefilter in front of the MPR 1900 filter will help extend the life of the high grade filter and prevent it from damage when you sweep the lint off the prefilter.

Figure 3 shows that a MERV 13 filter can have a lower flow resistance than a MERV 11 filter but that is not to say that it will ever have less flow restriction than a cheap fiberglass filter.  That's certainly not the case.  However, cheap fiberglass filters are simply lint filters and do nothing to protect your health.

 Side Note... Will a high grade pleated filter shorten the life of your furnace blower motor?
I won't go into great detail here but this is a good time to talk about filters verses fan motor life.    I tested several of the systems used in this test with no filters, with filters and with the inlet or outlet completely blocked.  In every case the squirrel cage blower motors drew much less power when completely blocked compared to  without any filters.  The axial fans drew about 10% more power when the air flow was completely blocked.    There are some furnace motor types that this  doesn't apply to but, even with those, the difference in power used will be very small.

You will hear almost every HVAC tech you talk to say, "high grade filters will kill your furnace blower motor!".  That is true if you allow the filter to completely clog to the point that it doesn't flow enough air to cool your blower motor.  It is not true otherwise.  In many cases, the motor will draw less power with a high grade filter.    My testing has shown that  some MERV 13 filters have a lower air flow resistance than most lower rated filters.  The only exceptions are the very cheap fiberglass filters that only remove lint and very large dust particles.

Conclusion:  
You should...
1. Use the   Filtrete MPR 1900  filter   which has a LOWER flow resistance and a HIGHER filtration efficiency than any other 1" filter I've tested if you can be sure to clean or change this filter before the flow rate gets too low.
​                               ---OR----
2.  Use an ultra cheap fiberglass filter that can get very dirty before it starts restricting airflow much at all.  These are unlikely to ever restrict airflow enough to overheat your furnace blower motor.

Don't use a filter in between because filters in between these two will restrict air flow more  that the cheap fiberglass filters and the Filtrete MPR 1900  filter   AND they will filter fewer particles than the   Filtrete MPR 1900  filter 
​
Who should use high grade furnace filters?
  • People who would never forget to clean and/or change their furnace filter
  • People who value clean air in their home or  workshop
  • People who don't mind paying extra $$ to maintain cleaner air 
Who should NOT use high-grade furnace filters?
  • Anyone who might forget to clean or change their furnace filters
  • Anyone who doesn't care about clean air enough to pay for more expensive filters
Systems Performance Detailed Summary
Let's start the countdown starting with the worst and working our way to the best...
​

​
#11 

No dust collection or air filtration
$Free (except for the cost to your long term   health)

Baseline Level

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#11  Of course, the least effective method was to use no dust collection and no air filtration.    However, the takeaway from this baseline test is to understand how unhealthy your workshop air can become after just a few cuts if you don't have effective dust collection and no air filtration.  Don't ignore this warning.  If you spend enough time breathing  high concentrations of dust it certainly will affect your health one way or another.  Most often people never connect the symptoms with the cause.


​​

​#10 
,   $29
​
Holmes HBF 2001DP-BM  20" box fan with one discount 2x20x20 "MERV 12" Filter

In my tests, the discount filter performed only slightly better than no filtration at all.   I only use 3M or Honeywell filters unless testing shows a different brand also performs well.  So far, only 3M and Honeywell filters have performed well in my tests.
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To #10 In almost every video I've watched showing how to build  "the ultimate box fan filtration system" they use cheap fiberglass filters or low grade filters.  I cringe when I see this because most of those systems will catch large particles but they do little to nothing to remove fine particles.    In some cases these systems may do more to keep very fine dust stirred up than anything else.

In this test I used a 20x20x2" discount MERV 12 Filter strapped to a   Holmes HBF 2001DP-BM   box fan.   The discount filter claims to meet the MERV 12 specification.  However, as you can see in Figure 4, the discount filter (with a claimed MERV 12 rating) didn't perform much better than using no filter at all!  I won't trust my health to  to filters rated less than MERV 11 or to brands that I haven't personally tested with satisfactory results.     I've tested 3M (Filtrete), Honeywell and discount filters.  The 3M and Honeywell filters have always met or exceeded their marketing claims. 

I ordered the discount filters  two separate times several months apart from Amazon just to make sure I didn't receive a defective product the first time.  Both  filters performed exactly the same.  I sent them back.  I suggest if you use any brand other than 3M or Honeywell directly from a big box store that you use an air quality meter to check to see if it performs to your expectations.  Try comparing different brands to see what  it reveals. 
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Figure 4   – Comparison tests
I won't trust my health to discount filters or discount brands unless I have tested them and they prove effective.  

Based on my testing, I trust 3M (Filtrete) and Honeywell filters.    They met or exceeded expected filtration values in every test.



​


​​

​
#9  ,   $126
WEN 3410
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#9     WEN 3410    - The 3410 is also a very popular model because it  is very inexpensive at $126 including shipping.  The WEN came in as the quietest option of the test but that is expected because it moved the least amount of air.  As with the Powermatic, the advertised 400 CFM flow rating is overstated.  I measured  257 CFM with brand new filters and 357 CFM with no filters installed.  In terms of filtration performance for the price it is on par with the Powermatic PM 1200 but you would need to buy 4 WEN 3410 systems to equal the performance of one Powermatic PM 1200 system.

The WEN 3410 took almost two hours to bring the dust concentrations below 30,000.  That means this system would be most appropriate for very small shed shops.   Even in a larger shop it is much better than nothing but it is only worth the $$ if you don't want to put together a DIY system yourself.

If you already have this system I suggest ditching the stock prefilter and building a custom intake frame so you can use a   Filtrete MPR 1900  20x24x1 filter  as the prefilter.   I didn't test the results but I'm confident that this will improve the performance of this system significantly by lowering pressure drop, increasing the flow rate and increasing the prefilter efficiency.

​


​​#8    ​     ,   $37 (as tested)
Holmes HBF 2001DP-BM  20" box fan,  3M MERV 6  filter   and one   MERV 11 filter    (stacked)

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#8     Holmes HBF 2001DP-BM 20" box fan,  3M MERV 6  filter and one MERV 11 filter (stacked).  The 3M MERV 11 filter is not shown in the picture but it was stacked inside of the MERV 6 filter.  This setup brought the particle count down to 30,000 in 65 to 75 minutes putting it in 7th place out of the 10 tests.  I ran the test twice without cleaning the filters in between and the  it took 10 minutes longer to clear the air in the second test.  This was likely due to a lower flow rate as the filters clogged with dust.

An interesting note about these results is that this system moves about the same CFM as the WEN 3410 and was only slightly more efficient at removing particles > 0.5 microns (outlet concentration/inlet concentration) but it performed about twice as well as the WEN.    Looking at these two numbers one would expect them to take about the same amount of time to clear the air.  So, why did it clear the air more than 50% faster than the WEN?  If you have any theories feel free to discuss them in the comments.  

Box fans pull  a LOT of air  into the front as well as blowing air out.  This makes it somewhat difficult to obtain reliable air flow rate readings.  It is possible that the air flow test readings were underestimating what was really occuring.  The efficiency readings are in line with the filter specifications so I believe that number is accurate.  Considering the profound difference in how quickly this system pulled particle counts down compared to the WEN it would be interesting to know exactly why.

This configuration is certainly the lowest cost and it is the easiest to implement.  For this test I used silicone box fan filter grips  to secure the filters to the fan.  You can also simply use duct tape to save a few  dollars and to gain a little bit more performance.

As I mentioned earlier, after completing these tests I found a set of flow-curves for furnace filters with various MERV ratings online.  To my surprise, some of the higher rated filters had LOWER flow resistance.    See Figure 3  for reference.  For this reason, if you want to use this setup I recommend using a   single   Filtrete MPR 1900  20x24x1 filter .  It will flow more air and  catch even more of  the small particles than the filters used in my testing.


​


​#7 ,   $198
Honeywell 50250-S True HEPA Air Purifier

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#7   The   Honeywell 50250-S True HEPA Air Purifier   is a true HEPA rated air filtration system designed for home use.    As the test results indicate this system captures 100% of all of the particles my system can measure.   The HEPA standard calls for the capture of 99.97% of all particles > 0.3 microns.  I included this unit in the test to see how the performance of a home air filtration system compares to a workshop and DIY air filtration systems.  To my surprise it barely surpassed the $37 box fan system.

To be fair, this HEPA filtration system will remove  some particles that a furnace filter can't such as very small smoke particles as well as some allergens that are too small for furnace filters.  However, for  most particles of concern the  box fan and floor   fan setups will outperform this system by a very wide margin.

The Honeywell system was slightly quieter than most of the systems tested by not by a noticeable margin.


#6,   $128
​The Shop Hacks 4 Filter System
 Single Stage Filtration System
With 2-year-old (dirty) filters!!


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#6   This system probably would have ranked #1 if I had installed clean filters but I wanted to test the Shop Hacks Downdraft Single Stage 4-filter System to see how a system with 2-year-old, dirty filters compared.   They haven't been swept clean in over 6 months and were used "as-is".  I designed this system to have ultra low pressure drop so that the flow rate doesn't change much as the filters get dirty.  The pressure drop across an air filter is proportional to the square of the speed of the air flowing through it.   A system with 2 filters should have 1/4th as much pressure drop at the same flow rate as a single filter system.  A system with 4 filters has 1/16th as much pressure drop   at the same flow rate as a single filter system!    Axial fans  produce less than a maximum of 0.2 in-wc of pressure.  To compare, a squirrel cage furnace blower produces closer to a maximum of 1.25 in-wc which is approximately 5x as much pressure as an axial fan.    For that reason it is possible to use less filter area for a squirrel cage blower  and still get the same flow rate as an axial fan.  The flow rate of a squirrel cage blower system drops off less than an axial fan system as the filters get dirty.  Quadrupling the filter area allows the axial fan to perform better than a squirrel cage blower.



​This will give you a feel for just how dirty the filters on this unit are.  I was surprised that it still removed 80% of the particles >0.5 microns and flowed over 1100 CFM even after 2 years of 24/7 use on the original filters. 
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At 60 minutes to bring particle counts below 30,000, this system came in mid pack.    I was quite surprised to see that the filters were still operating at 80% efficiency for particles > 0.5 microns after two years on the original filters.  I've swept them clean a few times  over the two year period but the filters were not cleaned prior to this test.  This says a lot for the   longevity of furnace filters.    With  that said, this is by no means a conclusive test for dirty furnace filter performance.  However, it is one encouraging data point.  As I mentioned earlier, the only way you can be sure what works and what doesn't is to purchase a particle counter and test your shop and home air yourself.  Using a particle counter allows you to see  the invisible, and with that information you will be able to make rational, verifiable, incremental changes until your air is always clean and safe.

If you plan to reproduce this system I recommend using the   Lasko 20" High Velocity Fan 2264QM   fan and 4  of the  3M Filtrete MPR 1900 filters.


​#5,   $500
​Powermatic PM1200

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#5       Powermatic PM1200 - This is a very popular model put out by Powermatic, a very reputable company known for quality products.  It is also the most expensive model tested, coming in at $500.  We wanted to include a top of the line mainstream retail system to serve as a baseline  to compare  the other systems.  The PM 1200 uses a squirrel cage blower that  flows around 865 CFM on high with the front grill and diffuser removed.  Powermatic claims 1200 CFM .  I measured  1200 CFM with both filters removed.  It is not uncommon for manufacturers to overstate performance by testing in an off-nominal configuration.  The system includes two filters.  The outer filter (prefilter) is similar to a pleated furnace filter and is rated to capture particles  5 microns and larger.  The inner filter is a bag filter rated to capture particles 1 micron and larger.  However, according to the test results it was quite effective at capturing particles down to 0.5 microns, the limit of the laser particle counter used.  The unit tested is a 2 year old system.  I cleaned both filters thoroughly with compressed air prior to testing.  

With the diffuser installed the PM 1200 took 41 minutes to clear the air.  It was much more effective without the diffuser, taking  a mere 30 minutes to clear the air.  That's  a 30% improvement by simply removing the diffuser!  

The diffuser does absolutely nothing to filter the air.  It only exists to lower the air velocity.  The diffuser prevents  high velocity  air from stirring up more dust in your shop.  However, it creates a significant pressure drop that significantly lowers the flow rate.  I suggest removing the diffuser if  the high velocity exit air stream doesn't  negatively impact your workflow.

If I had this unit I would ditch the stock prefilter and I would build a frame to allow use of a Filtrete MPR 1900  20x24x1 filter as the prefilter.  This will increase the filtration efficiency greatly  while  also increasing the flow rate  by at least another  150 CFM compared to the stock pre filter.

​


​#4, $38

20" fan drawing air in a window + a 20" fan blowing air out the door
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 #4      One   20" fan drawing air in a window + a 20" fan blowing air out the door ​ -  Simply placing one fan in a window drawing fresh air in from the outside and one fan in an open door blowing dusty air outside worked well.    However, surprisingly,  this did not outperform some of the air filtration systems.  One caveat to note for this test... the condition used to determine the time required to reach "good" air quality is when the particle count  drops below 30,000 particles per cubic foot.    During the time of testing, the outside air particle count was 36,000 so it was impossible to ever reach the "good" air quality mark using this method.  This system was ranked #4 based on the time required to drop the particle concentration below the "very unhealthy"  lower limit of 300,000 particles per cubic foot.

If you never use heat or air conditioning in your workshop then using a large fan to draw in fresh air and opening a door or window to allow dirty air to escape will be a very effective method of clearing your shop air.  This is contingent on the quality of the outside air and the flow rate of the fan(s) you used to accomplish this.    If your shop is heated or air conditioned then this method is very impractical.

Note:  When you draw air in you much provide a way for the air to escape freely or the fan will not move much air into the space.  An open window or door to allow air to flow out will suffice for most cases.





#3
The Shop Hacks Downdraft Table
4-Stage Filtration System
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#3 The Shop Hacks Downdraft Table 4-Stage Filtration System was the  only surpassed by the Lasko  2264QM V-configuration system.  I use this system as a multi-function table/workbench, a downdraft table,  a dust collection system for my table saw and a shop air filtration system.  It uses a 1200 CFM squirrel cage furnace blower and a 4 stage filtration system.  The first stage is a cheap 1" fiberglass  filter that is used to catch the large dust particles so I can sweep them off when the pressure drop gets beyond a certain limit.  The second stage is a 4" MERV 12 filter.  The 3rd and 4th stages are two MPR 1900 filters.  One of them is at the outlet of the blower to diffuse the airflow so it doesn't stir up dust in the shop.

This system moves about 600 CFM in this configuration.  It would perform better as a shop air filtration system if I only used 2 stages of filters.  However, since it is used as a dust collection and downdraft system it often sees very high concentrations of dust and I wanted to ensure that it would put out clean air even in the worst case conditions, which it does.  Using multiple stages of filtration also allows the higher MERV filters to last longer before needing to be cleaned.  I've been using this system over two years now and had only cleaned the last 3 stages of filters a couple of times prior to this test.  I replaced the second stage filter for this test.

It is best to use a squirrel cage blower for  multiple stage filtration systems.  Squirrel cage blowers produce up to 1.3 in-wc of pressure compared  to a max of about 0.12 in-wc for a 20" box fan.  The extra available pressure means that a system that uses a squirrel cage blower will lose less air flow as the filters get dirty than a system that uses axial fans and the same filter area.  



#2 ,   $85
​Lasko 20" High Velocity Fan 2264QM   with 2 sets of 3M MERV 6  filter and one MERV 11 filter (stacked)
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#2  Lasko 20" High Velocity Fan 2264QM   with 2 sets of one    3M MERV 6  filter   and one   MERV 11 filter (stacked).   This setup performed better than any other air filtration system in the test.  It was only topped by the test using my dust collection system.   ​
The V-Filter configuration was used for this test setup.  The V-Filter splits the flow between two sets of filters so the air velocity flowing through each set is  half that of the same system using only one set of filters.
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At $85 this system is a no brainer for anyone who has the space to fit the V-filter configuration and who doesn't mind a little bit of fabrication.    I simply cut three cardboard panels and duct taped everything together for this test.  That is all you need for a completely function system.  However, in a future article I'll expand on this idea to show you how to build a high quality system that looks and performs even better than this one.

Based on the information I noted in   Figure 3  regarding the superior flow and filtration performance of the   Filtrete MPR 1900  20x24x1 filter  , I recommend building  this system with that filter rather than the  filters I used in this test.  The performance should improve measurably and the system will drop another $20 also.

​

 Adding a 1200 CFM recirculation fan didn't make a measurable  difference in filtration efficiency.
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This system brought the particle count down to 30,000 in 27 minutes with and without   the recirculation fan.  I expected this would be the case because the very fine dust particles disperse  more like gasses than particles so they pretty much fill the space evenly regardless of how air is circulated.  This is not a definitive  test since I only tested one recirculation configuration and the recirculation fan was used on the second test  in which the filters had been loaded slightly from the first test.  However, considering the curves overlapped almost exactly with and without a recirculation fan, I doubt that any recirculation pattern will make a significant difference.​
The BEST and the WORST performers of the tests...
​Best of Test - Dust Collection -ON-         Air Filtration Systems -OFF-
 ---AND---
​Worst of Test - Dust Collection -OFF-         Air Filtration Systems -OFF-
The best results of all of the testing came from running my dust collection system.  Even after cutting twice as many boards as with any other test and with NO air filtration systems running the particle counts never moved out of the "good" air quality range.    The results are illustrated in Figure 5 below.
I ran tests on two other setups to serve as baselines.   They are...
1.  With dust collection only
2.  With no dust collection or air filtration


​Effective dust collection trumps effective air filtration because it is always MUCH easier to remove dust one inch away from the source than it is to remove it from the entire room.
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Figure 5  – Effective Dust Collection is   Imperative​
As you can see, using effective dust collection worked so well that I didn't even need to turn the air filtration systems on for this test even though I ran 2x as much material through the saw.  That's not to say that you should not use dust collection and air filtration systems in your workshop.  There are times when you just can't capture all of the dust at the source.  In those times the particle concentrations can rise quite high and having an air filtration system will bring them down  quicker which means you breath less dust in between cuts.

With no dust collection and no air filtration the shop air particle concentration remained in the dangerously high range for many hours.  Imagine making cuts one after another without dust collection or air filtration.  When I first bought my  Dylos DC1100 Pro laser particle counter   I routinely saw particle counts rise over the 6-million mark!  That's 6x higher than the highest level shown in any of the graphs for these tests.  There's no telling what I was doing to my lungs and body during all of those years.  Hopefully the effects can reverse, similar to the way smokers negative symptoms often  cease after they quit smoking.  Either way I know that I'm breathing healthy air now  and I rarely have to clean up dust in my shop which is a great side benefit.

All that to say, don't count on an air filtration system to replace effective dust collection.  In future articles I'll show you how to get nearly 100% effective dust collection on just about any tool in your shop with a simple and inexpensive shop vac.  Be sure to subscribe to the Shop Hacks newsletter HERE if you want to receive those articles.
Conclusions and Recommendations 
Empower Yourself - technical deep dive
(you can skip this section if you don't care to understand the "whys")



​For visual learners, a picture is worth a thousand words.    The graph shows one blower curve, one fan curve, one curve for the PM 1200 2-filter system without the front diffuser installed and one curve representing a 20x25x1" MERV 11 furnace filter from 3M.  
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Figure 6   – Blowers and Fans Have  Very Different Flow Curves
For those who may be interested, let me explain how to read the graph in Figure 5.    The orange line that starts at around 1.3 on the vertical axis and slopes down to 1200 on the  horizontal axis represents how the Powermatic PM 1200 blower performs.  If you block the inlet or outlet completely off that represents 0 CFM.  At 0 CFM you can see that the pressure is around 1.3  in-wc.  The dark curve sloping upwards in the middle of the graph represents the PM 1200 2 filter system flow curve.  The point where it intersects the orange curve is the operating point of  865 CFM and about 1.0 in-wc.  (In-wc stands for "inches of water column".  1 psi =  27.7 in-wc or 1 in-wc = 0.0036 psi.)  The upward sloping curve under that one represents the flow curve for a 20x25x1" MERV 11 3M furnace filter.  If you were to replace the two filters in the PM 1200 system with that furnace filter it would operate at around 1100 CFM and 0.3 in-wc.

The blue downward sloping curve near the bottom of the graph is the flow curve for the Holmes 20" box fan.  As you can see its maximum pressure is about 1/10th as much as the PM 1200 but when there is no resistance to flow it flows almost 1200  CFM also.  However, adding a 20x25x1" MERV 11 filter will drop the flow down to  just under 600 CFM.  As the filter gets dirty, its flow curve gets steeper which causes the fan to drop in flow rate faster than the blower.  This is why blowers are most often used in air filtration systems.  However, one way around this problem is to increase the filter area.  Doubling the filter area reduces the resistance to 1/4th.  Quadrupling the filter area reduces the resistance to 1/16th!  Once you get into that range  an axial fan can outperform a squirrel cage blower using 1/10th the pressure and 1/10th the power.

For reference
A typical  1.5 hp (10 Amp, 110V, 1100W) dust collector can move about 800 cfm with no resistance and produces a maximum static pressure of about 14 in-wc.

A typical full size shop vac  (12 Amp, 110V, 1300W)  can move about 200 cfm with no resistance and produces a maximum static pressure of over 100 in-wc.
Products  Used In These Tests
A Laser particle counter allows you to run your own tests to see where your dust is coming from and to optimize your dust collection and air filtration systems.  This particle counter will pay for itself many times over by allowing you to build your own dust collection systems without having to spend hundreds of dollars more for each system.
​

Dylos DC1100 Pro laser particle counter (Highly Recommended, measures down to 0.5 micron particles)
Dylos DC100 laser particle counter    (Recommended, lower cost but only measures  down to  1 micron particles)​
​
Holmes HBF2001DP-BM 20-Inch Box Fan (NOT recommended.   Although it puts out a little more air than the Pelonis, the cheap quality and rear mounted cord and controls make it more difficult to use)

3M MPR 1550 (MERV 13) filter 6 pack (Highly recommended for single filter box fan air filtration setup.  This will probably perform even better than the filters used during testing)
Filtrete 20x20x1 MPR 300 filter 6-pack (Used as pre filters in DIY filter tests.  Not recommended because they have as much pressure drop as the higher rated filters so they don't add much value.  However, they are very inexpensive and you can sweep them off without damaging them)
Filtrete 20x20x1, AC Furnace Air Filter, MPR 1200, Allergen Defense Odor Reduction, 2-Pack (these were used in the testing for this article.  They worked very well but I would recommend the 3M 1550 MPR filters over these since the 3M filters have less pressure drop)
Silicone box fan filter grips (I used these for the box fan filter tests.  They are recommended for simplicity of use)
Cardboard magnetic filter holder  (I didn't use this but it may be worth looking at if you you like a more finished look.  It certainly is not required to obtain good performance)

Retail air filtration systems and components tested 
Powermatic PM1200  air filtration system
PM1200 Inner Filter
PM1200 Pre Filter

WEN 3410   air filtration system
WEN 90243-027-2 5-Micron Outer Air Filters, 2-Pack
WEN 90243-026-2 1-Micron Inner Air Filters, 2-Pack

Honeywell 50250-S True HEPA Air Purifier
Honeywell 50250-S HEPA filter
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By buying products listed in this article (affiliate links) you don't pay any extra but Shop Hacks receives a small commission from Amazon which helps support the creation of more content to help you Build Your Space.  Thank you for your support.  Shop Hacks was not sponsored by any companies so you can be sure that all of the results in this article are completely unbiased.
28 Comments
Chris Board
4/27/2020 10:50:59 pm

Hello there ! Great article on air filtration! I am curious, would you recommend using the filtrete 2800 for the lasko fan? Or should I stick with the 1900? I have two of these fans already so it's a cheap build for me. I just want the best filtration possible. Your reply is appreciated! Thank you!

Reply
Shop Hacks link
8/9/2021 01:18:55 pm

The 2800 filters will filter finer particles than the 1900 but it will take longer and they will clog much more quickly. I haven't tested the 2800 filters but I talked to 3M and they said the 1900 filters are the best combination of flow and filtration efficiency.

Reply
Tony link
4/27/2020 11:29:49 pm

I don't recommend the 2800 filters because they will clog more quickly. The 1900 gives the best flow x filtration efficiency combination which should offer the highest overall performance overall time as the filters get loaded.

Reply
Tim
5/31/2020 05:35:24 pm

Great article. Been researching a DIY air purifier and was convinced you'd need a cylindrical/inline/exhaust type fan. I saw an interesting design that placed one atop a cylindrical HEPA filter. How do you think a 4-inch (depth) filter with some space between the box fan and filter (how much?) would perform relative to the 2x1-inch "V" design you built? Thank you.

Reply
Auren
6/3/2020 09:52:58 am

Hi, Im trying to build an air purifier as well and I agree that an inline fan seems to be a better choice, If you search in "cannabis grow rooms" youlle find many filters and fans.

Reply
Shop Hacks link
8/9/2021 01:17:00 pm

Axial fans move more air with less power but they also produce less pressure drop. If you don't use a very large filtration area with an axial fan it will not perform as well as a squirrel cage blower. I covered a wide range of combinations in the article. The Shop Hacks Ultimate DIY Air Filtration System performed the best by far. It is a well matched system. If you change an element you will need to run tests to determine if you are improving or decreasing the performance.

David Kirschner
8/13/2020 08:03:07 am

Thank you for such an insightful article. Just to help me understand, you V-shaped system performed the best in your test for purifying air. I am planning to buy your plans for the box-shaped set up assuming it would perform better than the V-shaped as long as I use new 1900 filtrete filters. Is that a correct assumption? Thank you again for your thorough article. David

Reply
Shop Hacks link
8/9/2021 01:14:10 pm

The V shaped filter system works very well but the flow rate will drop 25x faster than the 5 filter system as the filters get dirty. As long as you keep the filters cleaned out it will work well. The filters listed in the plans are the best combination of pressure drop and filtration efficiency.

Reply
Max Rockbin
12/7/2020 11:57:44 am

Great post! The testing is fantastic.

BUT...Wouldn't it make more sense to use a 2" or deeper furnace filter (they go up to 6" I think) instead of multiple 1" filters as in the ShopHack Ultimate system?

The object is to increase the surface area extending the life of the filters and actually reducing back pressure.

A deeper filter just has deeper pleats, increasing the surface area and having the same effect - in theory - as the Ultimate System.

Reply
Shop Hacks link
12/22/2020 01:45:05 am

Max, the 4" filters are typically MERV 12 vs 13, cost over 2x more, and have nearly the same flow resistance as the 1" filter I recommend in the plans. The filter I recommend has as much area as a 4" filter. It does this by making the pleats 4x denser.

I wanted to optimize for cost and performance. The filters I used accomplish both objectives.

Reply
Max Rockbin
12/29/2020 08:27:45 pm

Really great info. I looked up the California report you linked to. One interesting thing is a difference between brands. Like you say - Filtrete filters don't seem to get much more of a pressure drop with thickness. In other graphs in that study with different brands, FilterBuy actually did show a closer to proportional pressure drop between their M13 1" and 2" thicknesses. (Filterbuy - as far as I can tell is well thought of. Though WireCutter rated NordicPure #1 with NO testing of it at all so - grain of salt).

Filterbuy's 1" at 1500CFM has a drop of around .31, whereas their 2" is closer to .19. On that same graph, the Filtrete1900 1" is about .25 FilterBuy's 2" seems to cost about 10% more than the Filtrete, but I think they do a lot of promotions.

BUT... without testing of how well they actually filter, it doesn't mean much.

Kurt
12/30/2020 02:05:28 pm

I saw the same thing Max did, in the California Energy Commission test the FilterBuy 2 inch Merv 13 was the best performer. In checking prices it is even cheaper than the 3M Filtrete Filters ($13 vs $20) that ShopHacks has tested and recommended. I'd love to see ShopHacks test out the FilterBuy and give us some real world data.

Unfortunately I bought NordicPure for my shop built filter before I read this article and before I saw the CA Eng Commission report :(. So I'm shopping for some new filters.

Reply
Shop Hacks link
12/30/2020 02:21:59 pm

Kurt,

Great information. I'll buy some of the filters you recommend and test them. If they perform better I'll give you a free set of plans and a free hardware kit for anything at www.shophacks.com/shop.

I offer free plans to anyone who submits an idea or improvement that I incorporate into my plans. If this filter you recommend works better that's worth adding the free hardware too.

Thanks for the suggestion!

Reply
Andrew Aslesen
1/27/2021 12:32:27 pm

Hello, I'm thinking about buying your DIY air filter/purifier plans to build one for my surfboard shop. When I sand foam, I get a lot of fine foam dust and I'm worried that it will clog the filters quickly. Do you think this would be an issue? Is there some sort of course pre-filter that I could put over the filters that would catch the main stuff and be easier to clean regularly? Thanks for any suggestions you might have.

Reply
Shop Hacks link
8/9/2021 01:22:39 pm

You could use a fine screen as a prefilter or one of the see through fiberglass furnace filters. That would probably help with the situation you described. The only complaint I've heard regarding the filters clogging was a welding shop where the soot quickly clogged the filters. The only solution in that situation was to vent the soot outside and not try to filter it. I don't think foam dust would be a problem if you add a prefilter. A prefilter may not even be needed depending on how fine the particles are.

Reply
Chris Pederson link
1/29/2021 05:49:43 pm

You really connected with me when you brought up how you could have saved 3 hours of your life if you had a dust collecting system installed. I hate cleaning. Honestly, I'd do anything to have it as automated as possible.

Reply
Jason
2/5/2021 07:46:50 pm

Really great article! I was doing a little research for a diy system when I came across your article.

I have a similar size shop (slightly larger than 2 1/2 car garage). I was actually thinking of running duct work and placing the fan and filter system in my garage attic. I’d most likely run 10-12” insulated ductwork along with your recommended Lasko fan. I like the idea of keeping the fan/s and system upstairs just for space savings and the fan noise should be greatly reduced.

Do you think my system would work?

Reply
Shop Hacks link
8/9/2021 01:23:57 pm

You have to match the fan or blower to the ducting and filters you use. Otherwise there may be too much restriction and the system won't work efficiently.

Reply
Genevra Garrett
2/8/2021 01:48:58 pm

Thank you so much for the phenomenal article!

I need a follow up on where to place and angle my DIY fans for optimal cooling and air purification, given what you said about floor temp and positioning near an opening. My garage/workshop has no windows, but I could keep the door open or rig something to blow through the door vents. Thanks again!

Reply
Russell
3/28/2022 11:15:10 am

Yeah, I’d like more on optimal positioning/ placement

Reply
Chance Cook link
7/1/2021 10:37:41 am

I never thought about how a filtration system can help eliminate clean-up time. I just don't want to spend hours cleaning something after spending hours using it. That would take too much of my time for something that is supposed to be a hobby.

Reply
Colin
8/7/2021 10:49:14 am

I just learned that a MERV rating that does not have an “a” behind it - as in 13a - is relying on a temporary static effect of the filter material to improve the filtration ability. This wears off and the filter loses its effective MERV rating. Doesn’t seem easy to find these “a” rated filters or information as to how long the non ”a” filters are effective. Might help explain why some higher rated MERV filters seem to have a lower pressure drop - they may be low MERV with a static charge boost. How long before the static charge diminishes and to what MERV rating does it drop to? Seems like a way to cheat the MERV rating system to me but obviously that system created the “a” rating also so it was intentional.

Reply
Shop Hacks link
8/9/2021 01:10:57 pm

That is true but I ran the prototype for this system for almost 3 years 24/7 on the original filters. I vacuumed them a few times but they were caked with dirt. I tested them and they were still filtering at 80% efficiency for particles >0.5 microns. The flow rate had dropped very little. That's because of the huge filtration surface area. 5 filters produces 25x less pressure drop at a given flow rate than one filter. That's why this system rarely if ever needs filter replacements or filter cleaning.

Reply
Richard Ledwell
6/3/2022 02:04:21 pm

Is this a scam? I send for the plans and hardware kit, paid for both with a credit card and never received anything except a notice to download plans. No hardware kit or printed plans. I thought I would receive both but received nothing.

Reply
Shop Hacks
8/4/2022 08:49:03 pm

Richard,

My system shows that you downloaded the plans. They are PDF so you have to print them yourself.

I have a tracking USPS tracking number for the kit was sent to you. Please email me at [email protected] if you haven't received your kit and I'll send you another one.

I apologize for the late response. I don't get notifications for comments on articles to I just saw your comment.

Reply
JIm Dillon
6/21/2022 11:08:24 am

Great information. RE: potential overheating of fans with clogged or blocked filters, UL ran a test on cheap box fans with TOTALLY BLOCKED airflow and found that 7 hours' use with no airflow didn't lead to overheating, let alone a fire hazard. I often have heard people way that "UL Approved" just means the item won't burst into flames, and here's one example where that's exactly what we want to know! https://chemicalinsights.org/wp-content/uploads/DIY-Box-Fan-Report-2021.pdf?utm_source=Chemical+Insights&utm_campaign=d52ba63ea8-July_2021_Newsletter7_13_2021_13_4&utm_medium=email&utm_term=0_09fecf83d2-d52ba63ea8-119531236

Reply
Garrett Campbell link
10/7/2022 12:26:49 pm

Student stock just imagine enjoy. Study agreement myself do number argue.
Appear performance dinner learn view difference. Everyone account available green. Better everything theory.

Reply
Karen Iniguez
3/8/2023 12:48:11 pm

Thank you! This is amazing and I am a visual data geek. Living in a city outside of Mexico City that has not had rain in 5 months and at 7 k feet.. I am suffering from both pollution, pollens and lucky me.. cockroach allergies.. The HomeDepot here is twice the costs for any air filtration machines I own in Seattle. I have a round fan and this is the best site information and guide I have found for a DIY air quality filter that I can easily assemble! Thanks 🙏

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