Box Fan Dust Filter

[dkerfoot]

I wanted to build a home-made dust filter - the basic "attach a furnace filter to a box fan" type. Since no stores have box fans this time of year and we didn't have an old one laying around, I ordered one from Amazon. $25 with free shipping - not a great deal, but it beat waiting until spring.

My first thought was to attach a cheap "basic" furnace to the inlet side of the fan and a good 3M Filtrete electrostatic one on the outlet. It would have been perfect except for one thing... Nearly no airflow.

I tried attaching them both to the inlet side, with the 3M on the inside and it worked great! Until I realized there was still almost no airflow through the filters - it was coming in the outer rim of the front of the fan and then out the center.

So, I now have just the cheap filter on the outlet side. Still not great airflow, but better. But of course, it isn't doing much to trap the most dangerous and bothersome dust.

Any suggestions? I may try one of those super-cheap fiberglass type filters on the inlet and the 3M on the outlet and see how that works.

I also ordered the HF 2HP Dust Collector today which should help a lot.

[LCHIEN]

Originally Posted by dkerfoot

I wanted to build a home-made dust filter - the basic "attach a furnace filter to a box fan" type. Since no stores have box fans this time of year and we didn't have an old one laying around, I ordered one from Amazon. $25 with free shipping - not a great deal, but it beat waiting until spring.

My first thought was to attach a cheap "basic" furnace to the inlet side of the fan and a good 3M Filtrete electrostatic one on the outlet. It would have been perfect except for one thing... Nearly no airflow.

I tried attaching them both to the inlet side, with the 3M on the inside and it worked great! Until I realized there was still almost no airflow through the filters - it was coming in the outer rim of the front of the fan and then out the center.

So, I now have just the cheap filter on the outlet side. Still not great airflow, but better. But of course, it isn't doing much to trap the most dangerous and bothersome dust.

Any suggestions? I may try one of those super-cheap fiberglass type filters on the inlet and the 3M on the outlet and see how that works.

I also ordered the HF 2HP Dust Collector today which should help a lot.

Basically box fan designs are meant to work with very low restriction. generally no ducts and no filters on the input or output side.
Two filters = too much. those electrostatic filters also have more restriction than the fiberglass ones.

I guess that's why you have different kinds of blowers in the air cleaners. Mostly they use squirrel cage blowers.

[final_t]

What Loring said. Try using just one el-cheapo fiberglass filter on the intake side. You can also use the cheapest pleated filter, which should allow good airflow vs filteration comprimise - this is what I do, and it works pretty good.

[Pappy]

The HF dust collector comes with 30 micron bags. Not near enough filtration to protect you. Consider ordering 5 micron bags or look into the Wynn's conversion. Lots about it on the forum.

[leehljp]

I don't know what level of dust you want to get, but I have had success with a box ban and a standard fiber (about 3/4 in thick) AC filter. I cut it to size and put it on the back of the box fan; turn the fan on low. It does restrict the flow but a small amount of air comes out and the "pull" is enough to keep the filter pulled to the back of the fan.

I leave this on 24 hours a day and it does as well or better than AC filters on window/room ACs. It is not an "air cleaner" or expensive as one, but it does pick up the basic room floating dust. LOML said that she can tell the difference as well as not having to dust weekly - now every once or twice a month for the same amount of dust.

I am not sure of what you are looking to accomplish in having a box fan and filter but if it is to do general filtering, it will do that. If you are expecting the "air cleaner" size particles, I don't think that it will do that without more filters and stronger fan motors.

I have long thought about buying a Delta or other workshop air cleaner along the lines of what Pappy said and move it from room to room at times; probably will some day when I retire.

[drumpriest]

Before I got my ambient air cleaner I was using a 20" box fan with 20" furnace filters. I used pleated filters for it. I found that it was important to get a good seal all the way around the edge, as the air will take the path of least resistance. I agree with the others that you probably can't get any CFM with 2 filters. But mine sure did clean the air, just not nearly as quickly as the jet air cleaner.

I agree with others here too about the 30 micron bags, I can't stress enough how important it is to upgrade from those. All the 30 micron bag is going to do is pump the fine dust all through the air of your shop. The canisters are the best way to go, but also the most expensive, the bags help a bunch too for less $$$...

[siliconbauhaus]

I've been looking into making a air cleaner as the cost is out of reach at the moment. I'm going to build a box unit like the ones they show with the squirrel fans but I'm going to look at using a attic fan as an option as I think they'll be cheaper.

[leehljp]

Keith's post reminded me of something - I had four different kinds of filters but soon found that the more open 3/4 thick fiber filters on a box fan were more effective for us. I have a 1/4 thick black (charcoal) impregnated filter but it did not let enough air to flow through. I have the pleated filters too but with the cheap walmart $10.00 fan would not pull enough through it to be effective. The 1/4 in foam filters do OK but I think the 3/4 filters do the best job for us within the weak confines of the cheap fan that I have.

It really takes getting the right filter for the power of fan that you have. If you want a more effective filter, you will need a more powerful fan. By the time you move up a few notches in fan power, you may be getting close to the price of a room air cleaner.

[lum]

Around 1988 I installed an active electrostatic filter just above the fan housing in the forced air system for the home. This worked by charging rows of two-inch wide aluminum strips with very high voltage. Passing dust was attracted to those strips. The removable filter required a hosing in the backyard a few times a year.

The thing worked much like a bug killer.

Judith liked it. No dusting for months on end during the winter.

The air flow was unrestricted by the filter's parts ... those rows of strips of aluminum and wires between each row which charged the air.

The power supply for it resembled those found in a cathode ray picture tube TV set to generate the very high voltage.

I think I've seen free standing units for around $60 that lack a fan. Hence they are very quiet. Apparently, the air is pushed through by the charge.

Perhaps a plenum built around a filter like that and a box fan (which is reasonably quiet (I use two to exhaust our restaurant's kitchen) would make a low cost and easily maintained system that would push a lot of air per hour.

[eezlock]

I think that two filters would severly restrict the air flow and continued use would just burn out the motor premayurely. One filter on the inlet side should be all that is needed. eezlock