Best location for overhead air filter?

[mark mcfarlane]

I plan to add an overhead air filter to the new shop build. What's the 'best location'? In a corner? In the sanding/finishing area? How far away should the intake be from a wall?

My shop plan has 2 general work areas , left and top sides are for machines, disc and belt sanders on orange tables along top wall, bottom side for wood storage, and right side is for assembly and finishing. All the hand sanding will be done with Festool sanders, which so far for me are pretty much dust free.

Cosmetically. I'd like to hang the air filter in the lower left corner of the photo below, which is in the wood storage area. Alternatively I could but it over the sink (right wall), blowing the air towards the garage door.

[Sam Puhalovich]

Mark ... I would put it in the upper left corner about 2' from the walls ... that's about where I have mine ... in proximity to the saws.
I have a common 20" box fan ... hung horizontally ... with a MERV 7 filter attached.
I was majorly surprised how well it did ... so much so, that I did a upright floor version to use in the assembly area.

[Chris Damm]

It should be hung 1/3 of the way from a corner of the longest wall and near the wall for best air flow. These is what I have always read on the subject.

[Mike Chalmers]

It should be hung 1/3 of the way from a corner of the longest wall and near the wall for best air flow. These is what I have always read on the subject.

To improve the effect, I put a small fan on each wall near the ceiling to keep the air moving around the shop and carry the dust to the cleaner.

I am planning to move to a MERV 14 filter so I can dispense with the quite expensive and difficult to clean inner filter.

[Howard Acheson]

Here is some info that should be helpful.

Here are some general rules based on Nagyszalanczy's "Workshop Dust Control" and some of my own experiences and thoughts.

The two most important criteria for an air cleaner are the CFM and the filters. You want a CFM factor that will clean the size of your shop and a filter that removes the particle size that you are concerned about.

To determine the size or required air flow, use this formula: Volume of your shop (Length x width x Height) times Number of air changes per hour (typically 6 - 8) divided by 60. This will give you an answer in Cubic Feet per Minute which is how air cleaners are measured. MOST AIR CLEANER MANUFACTURERS RATE THE CFM OF THE FAN ONLY, but there are losses due to the filters. If you are building your own or if the air cleaner you are purchasing rates only the fan, figure you will lose about 25 - 40% for filtering losses.

As important as the air cleaner size is how and where you mount it. Try to mount at about 8-10 feet above the floor (no lower than 6'or 2/3 of the floor to ceiling distance if less than 8' ceiling). Mount along the longest wall so the intake is approximately 1/3 the distance from the shorter wall. Mount no further than 4-6 inches from the wall.

The exhaust is the largest determiner of the circulation pattern. You are trying to encourage circulation parallel to the floor/ceiling so ceiling mounting is not recommended. Use a smoke stick (or a cigar) to observe and maximize circulation. Use a secondary fan to direct air to the intake if necessary. Also, consider that a standard 24" floor fan moves a lot of air and, in some shops, just positioning it in a doorway with a window or other door open can accomplish as much or more than an air cleaner. It's all in the circulation patterns.

The exhaust is the clean air so that is where you want to position yourself. Do not place the air cleaner over the a dust producer. That will guarantee that the operator will be in direct line between the dust producer and the air cleaner. The operator wants to be in the clean air stream. If the dust has to pass your nose to get to the air cleaner, you get no benefits. If you have an odd shaped shop, two smaller units may be better than one large one.

DO NOT RELY ON A AIR CLEANER TO ACT AS A DUST COLLECTOR. The purpose of and air cleaner is to keep airborne dust in suspension and reduce airborne dust as quickly as possible AFTER THE DUST PRODUCER HAS BEEN TURNED OFF.

Finally, if you are looking for health benefits, you will not find any air cleaner manufacturer that makes health claims because there are few health benefits. CATCHING DUST AT IT'S SOURCE IS THE BEST LONG TERM GOAL. Rick Peters', author of "Controlling Dust in the Workshop", makes the point that spending your money getting the dust at its source is a better investment than trying to capture it after it is already airborne. If the dust is in the air, it's going to be in your nose and lungs too. Robert Witter of Oneida Air Systems has noted that "overhead cleaners can only lower ambient dust levels AFTER THE SOURCE OF EMISSIONS IS SHUT DOWN, and they take several hours to do this. This is why they are not used in industry." The absolute best answer, if health is the primary concern, is to use a NIOSH approved respirator. The dust cleaner will help keep your shop cleaner but have minimal or no health benefits. OSHA takes this position too. They measure the number of particles per a volume and most air cleaners will not satisfy their specs.

[Craig White]

image.jpgI placed an ambient air cleaner ahead of the HVAC intake.
Craig

[John K Jordan]

The instructions with mine said to mount it high, somewhere near the middle of a long wall to induce a circular air flow through the room.

This won't work when I move it to my new shop so my plan is to jack it up near the ceiling with a panel lift and experiment. If I can't get any of the special smoke sticks made for this I'll rig up something and see if I can judge if the air circulation effective in my planned position and tweak the position and rotation if needed before I mount the thing. Note that most can be mounted vertically, that is turned up on the side with the air still moving horizontally. That might be a better fit in some shops.

JKJ

[glenn bradley]

I think you will find most recommendations are to place the unit at about the midpoint of the long wall. This creates a circular flow pattern. Tucking the unit into a corner or in any position that does not allow and order of magnitude of the units length for intake and outflow will reduce performance. These units are not incredibly powerful and rely on ease of movement of the suspended particle air mass. The reduction will be proportionate to the deviation from the recommended installation method.

[John Lankers]

Howie is spot on with his advise, there are two things I would like to add:
A: No health benefit claims by the manufacturers. I am very sensitive to the smell of cedar and other softwood, the aircleaner completely eliminates this issue for me to the point where I would call it a significant health benefit. I do realize that if health benefit claims are being made it can open a whole can of worms though.
B: If you have a forced air heater or in your scenario most likely an airconditioner you have to take its airflow pattern into consideration so the two systems work in sync and don't interfere with each other.

[Bud Millis]

Put it in the center of the shop PERIOD (Think ceiling fan effect - there is a reason for this).

John/Howie - you stated, "A: No health benefit claims by the manufacturers." True. The reason being is these are designed to clean the fine particles from the "room" air, which takes time. Depending on the the size of the unit, CFMs, etc., the average unit will circulate the room air 10-15 times per hour cleaning the air. These were designed to be used as an adjunct to dust collection and not as a primary form of dust collection. This helps from all the fine particles floating around and landing all over - like when you come back in the next day and find that layer of film on top of every thing.

Mark, you'll need to decide on whats more important "Cosmetically," as you put it or your health.

Mike, your planning to move to a MERV 14 filter so I can dispense with the quite expensive and difficult to clean inner filter. I'd keep the inner filter, actually I have the inter filter running with my MERV 20. MERV 14 filters are good for smoking lounges as they typically filter to about 1 micron. Remember the smaller the micron the deeper into the lungs it goes. The MERV filter will collect alot, but there will be dust that makes it through, another filter is another layer of protection.

Redundancy is key; HEPA filters increase efficiency; and more is truly better.

Watch for my article on dust it will be out in one of the rags later this year.

Bud

[Mike Chalmers]

Put it in the center of the shop PERIOD (Think ceiling fan effect - there is a reason for this).

And the reason would be? Please state qualifications and/or substantiation for this comment which is not supported either by the instructions that come with the machine or by the vast majority of comments on this issue available on a search on the internet.

John/Howie - you stated, "A: No health benefit claims by the manufacturers." True. The reason being is these are designed to clean the fine particles from the "room" air, which takes time. Depending on the the size of the unit, CFMs, etc., the average unit will circulate the room air 10-15 times per hour cleaning the air. These were designed to be used as an adjunct to dust collection and not as a primary form of dust collection. This helps from all the fine particles floating around and landing all over - like when you come back in the next day and find that layer of film on top of every thing.

Pure logic would refute this statement. While your assertions are true (and obvious), any measures to remove particles is going to have some health benefit. Is it enough on its own? I think not. Is it worth doing? In my opinion, based on actual observance of the machine and the results obtained from it, definitely.

Mark, you'll need to decide on whats more important "Cosmetically," as you put it or your health.

A given.

Mike, your planning to move to a MERV 14 filter so I can dispense with the quite expensive and difficult to clean inner filter. I'd keep the inner filter, actually I have the inter filter running with my MERV 20. MERV 14 filters are good for smoking lounges as they typically filter to about 1 micron. Remember the smaller the micron the deeper into the lungs it goes. The MERV filter will collect alot, but there will be dust that makes it through, another filter is another layer of protection.

Redundancy is key; HEPA filters increase efficiency; and more is truly better.

All references I have found on the subject of MERV rates MERV 14 as effective for 90 - 95% of particles to .3 micron, not just 1, and good for such applications as operating rooms. This renders your comment regarding smoking lounges (no longer an issue in Canada) irrelevant. I would keep the inner filter, however, it should not have to be replaced very often. That is the bonus.

Watch for my article on dust it will be out in one of the rags later this year.

Bud

So, the overall objective of this post is to promote your article? Quite the opposite effect for me.

[mark mcfarlane]

Put it in the center of the shop PERIOD (Think ceiling fan effect - there is a reason for this).

...

Thanks Bud for the idea. Ceiling fans tend to be omni directional, whilst air cleaners are directional. Can you share your logic?