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Episode #56: Ambient Air Filter Modification

I’m not a gambler. I’ve never even been to Las Vegas, although I have heard good things about their buffets. But as any woodworker knows, taking risks in the workshop- not a good idea. The chances aren’t great that I’ll cut off my thumbs, but I’m still going to use a push stick. It’s the same with dust. Honestly, I don’t know if it will kill me. I do know people who have developed severe health problems from sawdust exposure. I also know people who say it’d much ado about nothing- which always surprises me. I mean, who says “ado” anymore? The way I see it, you have two choices. You can listen to the naysayers, roll the dice and hope you don’t pay for it twenty years down the road. Or you can take the safe bet and put some thought, and investment, into good dust collection. The former carries the risk of repertory illness, maybe even cancer. With the latter option you risk, what? A clean shop?


Now, I know dust collection can be expensive. Especially if you don’t know what you’re doing. I can’t tell you how much money I’ve wasted trying to save money. So we’re setting up a special section of our website to help you avoid the mistakes we made. ( There’ll be tips on different types of equipment, how to make some of it yourself, and other ways to save money so you can still afford to actually make some sawdust to collect.


Today we’re going to talk about upgrading an ambient filtration system. These things are really important, especially if you don’t have a powerful dust collector that captures all of the fine dust at the source. That fine dust is the dangerous stuff, and there are several units commercially available that will do a nice job at collecting it. You can also make your own and save a bundle, which we’ll show you how to do in a future video. Today, I want to talk about ways to increase its efficiency, and lower the maintenance costs.


The biggest expense associated with ambient air filtration systems, after the initial purchase, are the replacement filters. They cost $25-30, or even more, and they get dirty fast. These filters don’t have a lot of surface area to begin with, and as the dust begins to accumulate, the airflow through the filters become restricted. You may have spent money on a system that’s rated for your shop size, but get some dust in that filter and it’s no longer able to move anywhere close to the amount of air it says it will on the box. The only way to keep it working properly is to change the filters often, but like I said, that gets really expensive fast.

That got me thinking. What if I attached one of the big filters I use on my cyclone dust collector to my ambient air filtration system? Those things have a massive amount of surface area, so they will let more air flow through to begin with, and it will be nearly forever before they start to plug up. And the best part is, they can be cleaned many, many times. I figured one of those filters could save me a lot of money long term, and give me the peace of mind that my system was always working at peak efficiency.


So I got in touch with the company that makes my cyclone filters, Wynn Environmental. It turns out, they had been experimenting with that same idea and had it all figured out. Let me show you what they came up with.

Just about every commercially made ambient air filtration system, which we’ll call an AFS from here on out because that’s just too many words, comes with a pre-filter and a post filter of some kind. Both of them restrict your airflow, but we’ll deal with the pre-filter later. The post filter is what we intend to replace with a big cartridge, and that’s just a simple matter of attaching it to the AFS. Well, maybe not THAT simple, we will have to make some modifications. But before you do anything, you have to decide how you want your filter to be positioned in relation to the AFS. The easiest, and most efficient way, is to mount it directly in line with the system’s exhaust. But maybe you don’t have the room for that. Maybe you want your filter pointing to the side, or down a wall. Maybe you want the filter to be in a location that makes it easier to remove when it comes time to clean it. You do have some flexibility here if you duct your system to the filter. You should keep in mind that any ductwork will have a small effect on your system’s efficiency because it restricts airflow. Your AFS doesn’t produce enough pressure to compress the air, so the smaller the duct, the less air will flow through. This isn’t a huge problem because we’re going to be gaining a lot of efficiency with our filter modifications. The only reason I even mention it is because if you have a big shop and a tiny filtration system, you may want to mount the filter directly to the unit to squeeze as much power as you can out of it.


Now, we’ve produced a downloadable guide with step by step instructions for both ducted and ductless options for you to download from our website. But here’s a quick overview so you know what you’ll be dealing with.


For a ducted system you’ll need a 12X6X6 register boot, a length of 6” dryer duct, a 6” hose clamp, a 6” starter collar, a 6” pipe connector, some sheet metal screws, some weather stripping, a bit of plywood, some caulk, a pair of 10” discs cut from wood or plastic, some adhesive and some duct tape. All of that should cost less than $50. The biggest expense will be the filter. We’re using a Wynn 9L300 Nano filter, which provides a massive 300 square feet of surface space and is rated at MERV15- which means it will filter out bacteria, let alone dust. This is way better than any AFS replacement filter, but it costs about 5 times as much. Of course you are only going to be buying this thing once, it’ll last for many years. So in the long run you’ll save a bundle.


First we have to adapt the square grill on our AFS to our round duct. We do this with a piece of plywood cut to the size of our grill, plus a 1” border all the way around.


We’ll cut a hole in the center of the plywood to fit our register boot, which is secured inside the cutout with screws and sealed with caulk.


This assembly has to be mounted to the AFS, but you may find some screw heads in the way. Mark their location and use a drill to create a recess for each one so the plywood will lay flat.


Attach some weather strip around the parameter to create a seal, then use some sheet metal screws to attach the plywood over the grill.


Cut two 10-inch discs from wood or plastic. One of these gets attached to the flangeless end of your filter with adhesive. The other gets a hole cut into it to fit a 6” collar. Secure your collar with adhesive, then secure the disc to the filter with adhesive as well.


After everything is dry, it’s time to think about where you want to mount everything. A lot of people hang their ambient air filtration system from the ceiling right in the middle of the shop, or directly over their workbench. That’s not the best idea. For one thing, it’s going to pull all of that fine dust right past your face while you work, which defeats the purpose. It’s better to install it along a wall near the center of the shop. This will help the air to cycle throughout the entire space. Keep in mind that you’ll probably want to remove the filter to clean it, so mount it in a place that is easy to get at.


Simple wire is sufficient to hang the filter from the ceiling. If you are mounting it to a wall, use a pair of shelf brackets under the base and wire or a bungee strap to secure it to the wall.


Once the AFS and filter are mounted, all that’s left to do is connect them with a piece of 6” aluminum dryer duct. You’ll need a 6” coupling to attach the duct to the boot on your AFS unit. Use some good tape to secure everything. On the filter end you’ll attach the duct with a hose clamp for easy removal when it comes time to clean your filter.


That covers the post filter, now what about the pre-filter? These aren’t as expensive, but they are small. There’s not a lot of surface area for the air to pass through, so your system is only as efficient as your pre-filter. But you can double the surface area by simply taping two together in a triangle shape like this. Glue some cardboard to the sides to seal it up and use binder clips to attach it to your unit. You can buy inexpensive filters either from Wynn or your local hardware store. As long as they’re wide enough to fit your AFS, they’ll work fine. In fact, don’t buy expensive heap filters or anything like that. You want to let as much air through as possible. It only has to catch the big stuff like cat hair and that chisel you threw at the wall when you got angry.


Like I said, we made a step by step guide that you can download and print out from our website, You’ll also find answers to frequently asked questions concerning this project. In our next video we’ll show you how to make a meter to monitor the efficiency of your ambient air filter or your dust collector so you know when it’s time to clean the filters. See you then!






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