Rather than spend another small fortune on a fancy shop air filter, I thought I'd try making one with a fan and some furnace filters.
I had a Jet air filter previously. During one of the moves, I sold it rather than trying to drag it along with everything else. While it did a decent enough job filtering the air, it was really loud when it was running. Replacing the various filters also was costly and I still had a lot of dust that settled around the shop due to the air inlet only on one end.
I seriously looked at the various air filters available on-line that have filters on all 4 sides and use filters that are similar in size to furnace filters. They mostly run in the $275 range with ~1500 cfm or so of air flow.
Menards has a 19" ceiling mounted fan with a VFD that delivers up to 2,500 cfm. Perfect for what I wanted. I also picked up some 2x2's (which might have cost as much as the fan), a 2x4 ft piece of 1/4" plywood, a hook, a 4 ft section of pipe insulation, and 4 MERV 10 16x20 furnace filters.
The frame has slots cut into it for the filters to sit in. I also cut out a 19" hole and put the pipe insulation around it to seal around the fan to keep from pulling air thru the opening.
Initially, the intention was to use 2 cleats on the ceiling screwed into the rafters to hold things up. Unfortunately, the rafters are on 24" centers so the frame wouldn't hit 2 of them as it is only 21". Plan B was to use a single cleat, with a hole through it for the hook to hold the fan that would be anchored into the rafter.
Getting the frame installed and screwing the hook into the ceiling while juggling the fan took some maneuvering to ensure the cord could be fed under the edge of the frame.
After a few tries and a couple of beers (it was hot in the shop and I needed inspiration) everything was properly hung.
I bought some cord covers that stick to the wall and mounted the control box and then ran the feed cord to the outlet.
While the air flow is definitely reduced, there is still a decent breeze from the fan. It is not nearly as loud as the Jet unit was. If this works well, I may upgrade to the next higher MERV filters when they need to be changed. I'm also considering making a small one to use when I have to do router work on the bench, kind of a local air filter to catch the fine dust as it is being generated. Something like this could be useful for the lathe as a dust hood.
Nice, you won't regret it. Yours is much prettier than mine (as usual). My research found that the minimum filter you want is Merv 11 (see chart below). I went with Merv 13 because it was sort of the sweet spot between cost and efficiency. Going up to Merv 13 from 11 boosts the efficiency of 1.0-3.0 μm particles from 65-79% to over 90% and the 0.3-1.0 μm particles from under 20% up to 75%. I also went with 4" filters to improve the air throughput and reduce how often I have to replace them. My measurements of throughput indicate that my setup can filter the entire volume of my shop about 3 times in 15 minutes at the fan's highest setting. At 90% efficiency, that will theoretically get you 99.9% after 3 times through the filter. Likewise, getting up to 75% on 1 μm and below will get you to 98.5% after 3 times through the filter.
Another thing to note is that some fans can actually suck air from the front and sides of the blades which reduces the volume of air that it will actually suck or push through the filters. Using a cheap anemometer from Amazon, I verified this effect. As I moved the anemometer from the center to the edge (outflow side), the direction of the airflow actually reversed. The round shape of yours may prevent that but looking at the grating and how it curves back around the tips of the blades, I would not be surprised if it pulls a little bit of air in from the front around the sides of the fan. You may actually increase the air flow through the filter by making a cowling that covers the curved edges of the grate so that it cannot pull in air from the tips of the blades. An anemometer can help you determine if that is necessary. To see if you actually increase the air flowing through the filter, use the anemometer to measure at the filter surface how much air is flowing through it with and without the cowling.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
One more thought...It looks like the fan can be reversed so that it blows inward instead of outward. If you blow the air into the box, it may (?) be a little quieter and it also will collect the dust on the inside which helps prevent it from getting dislodged and fall back into the air. Another benefit is that in the winter, it will create less of an air flow that might make it a little chilly, especially when standing underneath it.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
Thanks for all of the info Nathan. I'm going to do some work in the shop today even though it's 90+ so I'll get a chance to see if it looks like it I'd doing anything. I'm a bit concerned that the flow drops off a lot with the small amount of pressure drop across the filters.
I'm also going to do some planing which will give me a chance to find out if my red neck grounding works or not.
We got a new Furnace, and AC unit a few years ago. AC went belly up, and replacement for just it, or both was only a wee bit more for both so we went that way. It has an attached "Air Bear" unit for an easy filter replacement which is a joy to have, versus climbing inside to pry the old one out.
Anyhow, I need to buy new to us 2" thick filters. The tech who services us suggest going here for filters Not saying you have to buy Air Bear type, just they have a huge assortment of sizes, and all different ratings, and for prices I can't buy local and get close. I ended up with what will end up being a MULTI year supply, and did get the free S&H, plus they email me with sale info on a regular basis, the sales are a good thing usually 50% or better off regular prices. Below are some regular prices.
With 90+ temperatures, you may want the fan blowing outwards, though since it is collecting warmer air near the ceiling, maybe not. In the winter having it blow outwards definitely makes it a little chilly out there.
4" filters will help reduced the airflow drop off. That helped a lot with mine. I recommend getting a cheap anemometer to check the air flow and whether it is sucking air in from the front and reducing the amount of air going through the filter. You can also use it to check whether the flow has dropped enough with dust accumulation that it is time to swap out the filters.
I have a couple of air quality meters that I use to monitor how well my filter is clearing the particulates from the air. I actually bought 2 units to give me a sense of whether they are providing accurate results. Both give similar results. This unit from Temtop is the one that I leave running full time in the shop. The M10i model logs history over the web that you can look at through their app. I recently knocked the M10i on the floor and broke it and I bought the M10+ model but unfortunately, it does not seem to have the logging feature. The other one is from EG. I mostly use to it to spot check. It also shows PM 1.0 and PM 10 levels on top of PM2.5. Both also measure VOC and formaldehyde levels. Those levels tend to spike when I use finishes in the shop and is a queue to open my garage door. You may find other units on Amazon, some which may also have data logging capabilities.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
BTW, I bought my filters from filterbuy.com. Comparable prices to what George linked to but significant discounts if you buy in bulk (shipping is free). One 20x20x2" Merv 13 filter is $35 but 6 of them is are $15 each. Similarly, 4" filters are $36 for 1 but $17 each if you buy 6. With over 3 times the filter surface area of a 1" filter. $17 each is a pretty good deal for a Merv 13 filter.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
I think the idea of reversing the fan will provide better dust removal. I don't feel much air flow standing below the fan which makes me think it is losing flow due to the pressure drop across the filters.
Some fans have different airflow curves depending on which side of the blade the air enters the fan. It is related to the blade type and pitch.
If you haven't already, get yourself a cheap anemometer and see if it is sucking in air in from around the edges in the front. I was amazed at how much air a basic box fan pulls in from the front side of the fan. As I moved the anemometer from the center to the edge, the anemometer actually reverses direction and the velocity is pretty high. That probably isn't an issue for moving air around the shop but it is if you are using it to pull or push air through a filter -- you are wasting that much air flow. I would bet that as the filters clog, it will pull even more air from the front side to make up for it. You could try, temporarily at least, attaching a piece of cardboard with a hole cutout so that only the flat part of the grill is open and see if that actually increases how much air goes through the filters. I used my anemometer to measure (estimate anyway) the total amount of air going through the filters as well. The fan I used for my DIY filter has a cowling that prevents it from sucking in air from the front side of the fan (verified with the anemometer). I also push air into my filter box so I know that any air going into the box has to exit through the filters so that I can measure the intake airflow to know if the flow is reduced due to clogged filters. When I stand under my filter, I can feel a slight draft coming down from the filter so I know that it is still cleaning the air, even a year and half later.
Also, I highly recommend going to thicker filters. Even 2" filters will help but my four 4" filters have been going for a year and half now with no noticeable reduction in airflow. If I had 1" filters, I suspect that I would not only have significantly lower air flow and poorer air cleaning but I think I would have probably had to swap them out 3 or 4 times during the last year and a half.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.
