Ceiling filtration or exhaust fan?

[Malcolm Schweizer]

I just bought one of those hanging air filtration units for my shop. My attempt at an exhaust fan failed due to poor CFM from my cheapie fan. I lit some paper and let it smoke and 5 feet from the fan I saw no movement at all. The dust filtration unit wasn’t much different in cost to a better exhaust fan, so I bought one. Should I hang the unit over the bench and just filter the air, or should I take the filter out and aim the unit out the vent above the door and just blow the dust out of the shop? The door exits to the street, and this is a shop in my house where already I take measures to collect dust at the source, so this is just added protection. I’m not going to be blowing tons of dust out of the shop.

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[Alan Jones]

I would be inclined to collect it at source rather than risk any complaints

[Malcolm Schweizer]

Clarification: photo shows the existing fan. Filtration unit has not arrived yet.

[Jon Nuckles]

Let me preface this by saying that I am not an expert, but don't you need make-up air to get good exhaust movement? Maybe the cfm moved by one of these is easily made up by normal air infiltration, but it is worth thinking about. Obviously not an issue if hung above the bench.

[Malcolm Schweizer]

Let me preface this by saying that I am not an expert, but don't you need make-up air to get good exhaust movement? Maybe the cfm moved by one of these is easily made up by normal air infiltration, but it is worth thinking about. Obviously not an issue if hung above the bench.

great question! The shop is in my downstairs which is open-air. Windows are open. The interior door has the same vent over it. My idea is create airflow out of the shop, drawing air in through this door/vent. I am probably just going to first try it with filter but aim it out the vent. Kind of a best of both worlds solution.

[John K Jordan]

I just bought one of those hanging air filtration units for my shop. My attempt at an exhaust fan failed due to poor CFM from my cheapie fan. I lit some paper and let it smoke and 5 feet from the fan I saw no movement at all. The dust filtration unit wasn’t much different in cost to a better exhaust fan, so I bought one. Should I hang the unit over the bench and just filter the air, or should I take the filter out and aim the unit out the vent above the door and just blow the dust out of the shop? The door exits to the street, and this is a shop in my house where already I take measures to collect dust at the source, so this is just added protection. I’m not going to be blowing tons of dust out of the shop.

Do you mean an air cleaner/filter like the Jet that hangs from the ceiling? Mine came with instructions as to the most efficient placement to induce air circulation, generally near a long wall if possible. As well as hanging, they can also be turned 90 deg and mounted on the wall. If air conditioning/heating losses were not an issue, I might be even inclined to try running both the air cleaner and the exhaust fan at once with the intake of the filter towards the dust generation and and the wimpy exhaust fan downstream.

If the budget can stand it a Dylos air quality monitor (laser particulate counter) will let you objectively analyze the before-and-after of various configurations. If the air filter is the Jet box type, you might be able to prop it up on a ladder (or a pallet jack) to test the effectiveness of candidate positions.

https://www.amazon.com/gp/product/B004AWEG0Y

I found the jet air cleaner worked very well, not for immediately clearing fine dust but for clearing the air after I left the shop for a while. Particle counts drop back to ambient in about 1/2 hour or so. (This was in my temporary garage shop when I used a shop vac, before the new shop with the big cyclone.)

JKJ

[Jim Becker]

Malcolm, you have a bit more challenge here simply because of the "open air" nature of your shop. The air filtration units are really good at what they do, but they function by circulating air in one end, filtering it and sending it back out the other side. Rinse, Repeat. Rinse Repeat. When the room isn't "closed" you don't get quite the same level of filtration benefit because how the air moves around more on it's own. In your case, I strongly suspect that you'd get more benefit from a heftier exhaust fan that provides substantially increased cross ventilation so that air coming in one side goes flying out the other side, taking suspended particles with it. That combined with collection at the source as best as you can likely will provide the most benefit. I'm not saying you will not benefit from the filtration unit; 'just that it might not be the bee's knees in your situation like it would be in my shop which most of the time is "closed" up with captive air to filter over and over.

[Brice Rogers]

I have an 800 square foot shop. I use a 2 HP dust collector with a home built separator and vent directly outside. I also have a window fan with a couple of furnace filters that blows semi-clean air at me when I'm creating dust (typically sanding on a lathe). I also have an attic mounted "whole house fan" that I sometimes turn on to bring in fresh air and to clear drifting particles. It has enough suction that if the door isn't latched completely it will open by itself and if I stand in the doorway I can feel quite a breeze. I also often where an N95 respirator, especially if I'm working with some types of woods that can be a nasal irritant. Kind of like wearing a belt and suspenders - - but my equipment is not high-end/high performance so maybe it makes sense.

[Malcolm Schweizer]

Thanks for the great replies. John, yes- this is a filtration unit that hangs from the ceiling. Jim- good points. Brice- I was going to use a whole-house fan, but they were (a) expensive, and (b) quite noisy.

I'm now even more thinking the best thing is to keep the filter in at first, but aim the exhaust towards the vent to the outside. I looked at lots of exhaust vent options and all of them were either really pricey or noisy, or both. I got a deal on this thing and it was remote control which is a plus, so I just bought it and figured it can't hurt. Surely it will provide some additional dust protection.

I really do not make a whole lot of dust in my little shop, but my brother's father-in-law, who was a long-time woodworker, recently died of lung cancer. He didn't smoke. I'm quite sure wood dust contributed to his condition. I was mixing up some epoxy with microballoons and microfibers, and the powder was hovering in my shop and I thought, "I need to do a better job with air filtration." I am meticulous about wearing a dust mask, but stuff hangs around and who knows what the cumulative effects of breathing tiny amounts of this stuff is, but it can't be good. I looked at these filtration units and found a deal on one with shipping at a reasonable rate. It's on the way. I'll post an update when I install it.

[Art Mann]

I use an Air King 9166F window fan in exhaust mode to eliminate wood dust in good weather. It is highly effective in my 864 square foot shop.

[Chris Parks]

Unfortunately you can't move a lot of air without making a lot of noise. The only way it might be mitigated to some extent is via ducting with the fans outside the workshop and in the ducting, how about some big fans from old air compressor units inside home made ducting, it doesn't need to be round duct it can be rectangular and made from thin MDF for a cheap approach.