Preview - The Shop Hacks Ultimate Air Filtration System

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Several weeks ago I presented the test results from tests of 10 different air filtration systems.  The results were  amazing and a  $100 DIY system beat the $500 Powermatic PM1200 air filtration system by a pretty wide margin.  You can read that article HERE.  Below is a summary of some of the performance results from that article.  Particle counts were logged using a laser particle counter.  All tests were performed by 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 more dust).  For reference, the green band at the bottom of the graph is where you want your shop air to be for a healthy environment.  Anything above that band is unhealthy.

I learned a great deal during the air filtration system testing and  I'll distill the most important findings in this article.  I learned enough to design a system that you can build yourself that will outperform the equivalent of two $500 Powermatic systems!  Next week I'll present  the Shop Hacks Ultimate Air Filtration System   in a "How-To" article.

This article is laid out as follows:

1. How many filters are ideal and why?
2. Which filters and fan to buy?  You can have them ready to build this system as soon as the plans are released next Friday!
3. Cost and performance compared with the $500 Powermatic PM1200.  (Spoiler alert... this system is going to blow the PM1200 away in cost, features, and performance!)

How many filters are ideal and why?
The surface area of your filtration material matters.  It matters a lot.  Each time you double the  filter material area you cut the  flow resistance at any given flow rate down by 4x.  If you increase the filter area  by 4x you decrease the resistance 16x.    Increasing the filter area by 10x decreases the resistance by 100x.  You get the point...  put mathematically, the flow resistance at any flow rate decreases as the square of the filter area. 

What does this mean in practical terms?
​For a 20" box fan the flow using 1, 2 and 4  @ 20"x20"x1" new (clean) filters is...

• 1 set of 2 filters stacked (as tested) - 375 CFM
• Using THIS filter...
• 1 filter - 500 CFM
• 2 filters in a V-configuration - 750 CFM
• 4 filters in a box configuration -  900 CFM

For the Lasko High Velocity Fan

• 2 sets of two @ 20"x20"x1" filters stacked (as tested) - 1300 CFM
• 2  each of  THIS filter in a V-configuration - 1750 CFM
• 4 each of THIS filter in a box configuration -   1850 CFM  (equivalent to 2 Powermatic PM1200 air filtration systems costing $1,000!

As you can see, the benefits of adding more filters drops off after two filters.  However, dirty filter will have about 2x the resistance of a clean filter.  This means 

• A 4 dirty filter system will flow the same as 2 clean filters
• A 2 dirty filter system will flow the same as 1 clean filter

So, a 4 filter system with dirty filters  will perform 35% better than a 2 filter system with dirty filters.  I have a 3 year old, 4 filter system in my shop and I've only swept the filters a few times and it still  performs very well.  It is nearly a no-maintenance system.

For this reason, the Shop Hacks Ultimate Air Filtration System will be modular.  You can use 2,3, 4 or 5 filters with it depending on  your  budget preferences.  That will allow those who want to save some $$ to use just two filters and those who want the least amount of maintenance and the highest performance to use 3, 4 or 5 filters.

What Fan and Filters Should You Buy?
After running the Air Filtration Shootout Tests I realized that lower MERV ratings do not mean that filters will have lower resistance to flow.  In fact, THIS filter, when clean, has a lower flow resistance than ANY filter I've tested, including cheap fiberglass filters.    I found this test data to back up this notion...

So, the stacked MERV 8 and MERV 11 filter configuration that I used in the Air Filtration System Shootout was both more restrictive and filtered fewer particles than a system using THIS filter alone.  I'll link to the fan that I'll design the Shop Hacks Ultimate Air Filtration System around below also.

​If you want to have your materials ready to start building with the plans for the Shop Hacks Ultimate Air Filtration System comes out next week then  purchase the following:
2, 3, 4 or 5 of these   20"x25"x1" filters    (the link is for a 2-pack).  Higher or lower rated filters will NOT flow as well as this one.   You want this exact model.  If you want one for your furnace you can choose a different size but use this model.

The Shop Hacks Ultimate Air Filtration System will be designed around THIS fan if you want to have it on hand to build the system when the plans come out next week.  With a 4 or 5 filter setup, this fan will flow around 1850 CFM and achieve over 85% filtration efficiency for particles 0.5 microns and larger.  This is the equivalent of two Powermatic PM1200 systems ($1,000) for under $200.

I look forward to presenting the Shop Hacks Ultimate Air Filtration System design and a link to the plans to you in next week's article.  If you have any questions in the meantime, please leave them in the comments section below this article!  I'll be happy to help you out.

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