Air-Filtration Systems

Scrub your shop air of the superfine dust left behind by a dust collector or shop vacuum. Then breathe a healthy sigh of relief.

WOOD Magazine Staff July 13, 2020

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You can't help but create airborne dust when cutting or sanding wood. It's the pesky side of woodworking, the fly at the picnic. And that's where an air-filtration system comes to the rescue. This machine, typically suspended from the ceiling, draws dust-laden air into the front of the unit and through one or two filters, exhausting (hopefully) clean air out the back. To help you find one that works well, we tested nine models head-to-head. We also threw in a common shop hack: a $20 box fan with a $20 furnace filter. The results might surprise you.

Airflow starts the process

Use an air-filtration system as a supplement to a dust collector and shop vacuum that collect debris directly from the machines and tools that create the mess. Do not rely on one of these units as your primary source of dust collection.

Before one of these machines can filter the air, it must first suck in the air. Lots of it. To measure airflow, we took readings at the intake filter in 12 spots using a digital vane anemometer, and then averaged the results. We measured each machine's airflow at all of its multiple speeds; the Grizzly G5955 has only one speed. We tested all models with brand-new filters, and then again after each dust-collecting trial, cleaning the filter each time with compressed air.

As you can see in the chart (below), the two larger units, the Jet AFS-2000 and Grizzly G9956, created the highest airflow. (Generally, the larger the unit, the higher the airflow.) Naturally, all models moved the most air at their highest speed, and that's where we recommend you run most of these models, unless you find yours too noisy. None were loud enough to require hearing protection. And the Powermatic PM1250 was so quiet we almost didn't believe it.

With each unit, airflow dropped off as dust built up in the filters—especially the prefilter—but three (Shop Fox W1830, Supermax 810650, and Powermatic PM1250) fell off less than 10 percent. The box fan dropped off the most, eventually stabilizing at 30 percent, followed by the Rikon 62-400 (28 percent) and Powermatic PM1200 (23 percent).

The air-handling industry recognizes air changes per hour (ACH) as a standard of how often a machine can move all the air in a fixed space. Manufacturers suggest you need 6–8 ACH for acceptable ventilation.

To determine the ACH a machine will provide for your shop, multiply a machine's airflow (in cfm, from the chart above) by 60, and then divide by the cubic feet of the room (length × width × height). For example, in a 24×24' shop with a 9' ceiling (5,184 cubic feet), the Jet AFS-2000, pulling 1,178 cfm, will achieve 13 ACH. But, for this same shop, you'd need two units if using the Grizzly G5955, Rikon, Shop Fox, or box fan, to hit the minimum 6 ACH.

We tested these systems in an 850-cubic-foot shop space walled off with plastic floor to ceiling. Then we sanded MDF with a drum sander using 120-grit sandpaper, and no dust collection. When the air was saturated at 6 million dust particles per cubic foot, we ran each air cleaner until it cleaned the air to the "control" level.

Filtration clears the air

The smallest dust particles we can see without magnification measure about 10 microns. (Human hair typically measures about 40–60 microns in diameter.) Particles smaller than 10 microns can stay suspended in the air for 30 minutes or longer—ripe for you to breathe in.

All that airflow means nothing if the unit doesn't capture the particles in the air. The chart above shows how well each machine filtered dust in our trials. Both Jet units scrubbed the air in 13 minutes at high speed. Curiously, both Powermatic models cleaned the air about 60 percent faster at their slowest speeds. Powermatic's Tobias Bridges said he did not know why this would happen, adding that both machines typically clean the air faster at the faster speeds. The good news: Each machine was able to return the air to the control level. Obviously, the larger the shop space, the more time each machine will likely need to clean the air.

All the rectangular-box machines have a prefilter and secondary pocket filter. Both are easily accessible for cleaning.

Furnace filters are rated in terms of a Minimum Efficiency Reporting Value (MERV) number. The higher the number (from 1 to 16), the better its filtration effectiveness. Woodworking machinery filters might not always specify a MERV rating, but will typically rate the finest size of particle, in microns, they can effectively trap.

Eight of nine tested air-filtration systems have two sets of filters, as shown above. The prefilter, made of spun nylon or pleated fabric, captures larger dust particles (5 microns or larger), and can be cleaned with compressed air or a shop vacuum. Most prefilters will eventually need to be replaced after cleaning no longer improves their performance. (The Powermatic PM1250, below, has a screen rather than a traditional prefilter.)

Powermatic's PM1250 looks similar to a box fan, but has a high-efficiency spiral electrostatic filter behind a fine outer mesh screen that serves as a prefilter.

The inner high-efficiency filter consists of large "pockets" of dense fabric to trap particles that get past the prefilter. You also can clean these with compressed air; read the owner's manual before cleaning. Because replacements for these filters cost 4–5 times more than the prefilters, be sure to keep the prefilter clean or replace it often to preserve the inner filter.

When cleaning a filter with a vacuum, make sure its filter traps the fine dust you remove, rather than simply returning it to the shop air. If your vacuum can't pull this off—or when using compressed air—clean the filter outside where dust can vent into open air.

As dust particles build up on the filters, airflow drops off, but filtration improves. So you'll have to find a good balance between adequate airflow and filtration. We suggest erring on the side of caution and cleaning the prefilter about every 7–10 days of working in the shop.

Details add convenience

■  Remote control. With a couple of exceptions, you can turn the unit on or off, control the fan speed, and even set a timer that turns it off automatically via a panel on the unit, or by remote control. (Grizzly doesn't provide a remote control for the G5955, although you can buy a radio-frequency [RF] model as an accessory. The Grizzly G9956 provides the functions on its remote control only.) We prefer the RF remotes on the G9956 and both Powermatic units, which control the system from anywhere in the room, to the others' infrared (IR) remotes that require line of sight to the control panel.

■  Airflow indicator. The Supermax has a gauge that indicates when the filters become too clogged to clean the air effectively. The Powermatic PM1200's indicator light warns you of the same thing. No other units have this feature.

Filter upgrades can save an air cleaner

Curious to see if an upgraded filter would improve performance on these air cleaners, we tested two units with aftermarket prefilters (MERV 7) and high-efficiency pocket filters (MERV 15) from American Fabric Filter (877-742-3653, americanfabricfilter.com). The Jet AFS-1000B actually performed better with its original filters, requiring nearly twice as much time to clean the air with the AFF filters. However, the Grizzly G5955 improved vastly from 213 minutes using its original filters to just 33 minutes with the AFF filters. Our advice: If your air cleaner's performance falls below expectation, consider upgrading to these aftermarket filters. The aftermarket prefilters costs $3 each, and the high-efficiency pocket filters cost $35 apiece.

Let's clear the air

Our Top Tool recommendations come in two sizes. First, the Jet AFS-2000 proved best overall with the top airflow, fast filtration, and the largest filters (fewer cleanings). But its large size could make it unrealistic in some shops, particularly those with a low ceiling. So we also grant Top Tool status to the Jet AFS-1000B as best among the midsize units.

Our Top Value: the box fan. With no frills, and equipped with a MERV 12 filter, this fan outperformed or equaled several of the dedicated air cleaners, and at a significantly lower price (about $40 with a filter). Don't skimp on the filter! Get one rated at MERV 10 at a minimum. A filter rated higher than MERV 12 will increase dust pickup, but likely lessen airflow.