Shop air cleaner

[John T Barker]

I'm looking to build or buy an air cleaner for my shop. I notice some build videos on youtube use attic air fans and the like. Anyone have any input on good choices/bad choices on this? They seem to pull more than enough cfm's. I'm trying to keep the costs down so I don't want to be over $75 for the fan. Do I put myself into the land of quick dying crap at that price?

[Mike Schuch]

Search ebay and craigs list for electostatic smoke eaters. These were used to filter cigarette smoke from bars and restraunts back when it was legal to smoke in such establishments. I picked up my smoke eater for $200 off ebay several years ago. It was a $1500 unit new. They give the air going through the filter a high voltage negative charge. Then the air flows through a set of positively charged plates and all the micron sized particles stick to the positive plates like glue. I periodically pull the positive grid, thoroughly wet it with 409 then hose it off (Running the positive grid through the dishwasher also works great!). It is amazing the amount of incredibly small particles it collects! It is by far the best shop filter I have ever seen! It is also great for cleaning up the air when I am welding.

[Sam Puhalovich]

John, try this ... a ordinary 20" fan with a 20" filter attached to the suction side ... it'll surprise you.
Julie Moriarity did a test study on air cleaners that you should be able to find.
I had already had mine up for two years at the time she did her evaluation; and I knew what kind of results she was going to have.
After about 6 months that the ceiling fan was up; I decided since it worked so well that I would set-up a floor model that has, also, worked-out very well.
A lot of the 'fines' that I was letting float off-and-around were from hand operations that seemed trivial and the occasional use of the jig saw.
After a few weeks there was a noticeable brown shade to the filter. I use it even when I use the ROS at the down-draft table: set-it-up-on-top adjoining the work.
I paid $20 apiece for the fans and use MERV 7 filters that I clean about 3 months to ensure they sustain ability to pass air.
And btw ... I am rabid about dust collection ... basement workshop ... ClearVue DC ... 4 shop vacs ... and a plenum filter on the house system.

[David Falkner]

Mine is mounted from the ceiling and I can swivel it for changing direction but it works pretty good for an air cleaner (fan is mounted upside down so I can easily reach the switch). Total cost was about $35.

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[John T Barker]

I appreciate the responses. Sam, Dave, my understanding was, from threads here, that ordinary fans like that don't do the job. My memory is not enough cfm's and once the filter got a little dust on it no air pull.

[Jim Finn]

A squirrel cage fan is much more suitable to moving air through a duct or a filter. I have a unit, designed for cleaning air, mounted to the ceiling of my shop that I bought years ago from Grizzly. Mine cleans the whole shop full of air every six minutes. I paid $175 for mine.

[glenn bradley]

I built one using a gable fan that is rated at 1650CFM. this is greatly reduced once it is put into a fixed airway with filters in the path. As John F mentions above, if I were to do it again I would use a squirrel cage fan. As others have mentioned, even with a cyclone for the machines there are plenty of activities that don't involve machines. I also use a vac with a Dust Deputy for hand held power tools and I am amazed at how much an ambient cleaner picks up during some operations.

[John Donofrio]

I built mine around two Dayton 10" axial fans rated for 665cfm each (search ebay for dayton 10" axial fans, I see some there now for $59ea). As Glenn stated above this type of fan is not very good at overcoming static pressure and when building it I was figuring it would move about half the combined cfm (600cfm+-). The best I can tell it's actually moving about 300-400cfm passing through a 24"x12" electrostatic pre-filter and a 24"x12"x12" one micron pocket filter. At that rate the air in the shop (22'x22'x9.5') would be cycled through it about every 12-15 minutes. Not quite as fast as recommended but I find it acceptable and the Dylos meter seems to confirm this. They are quiet too, nothing more than a little white noise.

I have a 1,2,4,8 hour timer on it and always have it running while making dust and for eight hours after I leave. I can tell you it does capture quite a bit of fine stuff, especially the pre-filter. When I clean it, first with compressed air and always outside, the amount of super fine dust is impressive. I'm sure a squirrel cage fan would move more air and work better but...

[David Hawxhurst]

i think the ultimate homemade one is using a wynn nano 9l cartridge filter and a inline blower fan motor. seal off one end of the filter place fan on a seal on the other end and maybe add a swivel so you can direct the air flow as needed. bill pentz's website has a more detailed description on how to build it.

[John T Barker]

What is the advantage of the squirrel cage fan?

[cody michael]

to make a reasonably cheap air filter, would it work if you took a 1 micron dust collector bag, and fit it over the output from a squirrel cage setup?

[glenn bradley]

What is the advantage of the squirrel cage fan?

As best I understand it a centrifugal (squirrel) fan will develop much more static pressure than an axial fan. In a ducted environment (like in a tube, duct or air cleaner housing) the ratio is about 5 to 1 in the ability to shove an air mass through a restrictive space. The usual cornucopia of variables and ranges of actual numbers apply :)

[John TenEyck]

Whatever you build use a HEPA filter or equivalent MERV rating. Otherwise you will remove some coarse particles but continue to circulate the fine (read potentially health harmful) particles around your shop. I bought a HEPA filter from Grizzly and built my own fine particle filter using a squirrel cage blower I had lying around. It helps clean the air but is no substitute for dust collection at the source.

John

[Prashun Patel]

The squirrel cage style fans are more powerful at moving air through filters. The box fans choke down easier. However, the squirrels are heavy and bulky and are usually mounted to a wall or hung from a ceiling.

The box fans are arguably more mobile and can be positioned near the point of purchase. I used box fans with filters for sanding and rasping and they work extremely well.

[Jim Finn]

What is the advantage of the squirrel cage fan?
A squirrel cage fan produces much more static pressure than a propeller fan does. That is why they are used in your furnace or in any ducted system, including dust collectors. Propeller fans should not be ducted and work best when not obstructed in any way... like with a filter. Squirrel cage fans are usually quieter also.

[Bill Adamsen]

I built one using Bill Pentz' design (http://billpentz.com/woodworking/cyclone/air_cleaner.cfm) and it was reasonably priced (not cheap but great value) and works exceptionally effectively.

[Keith Westfall]

I built one (more than a) few years ago out of an old furnace fan/blower. I built a box on wheels at a height that I could comfortably put my 12" disk sander and osculating (spl) sander on. On 2 sides I put a double layer of furnace filters and have it exhaust through the bottom of the stand.

I could probably have better filters, but it cleans the shop air pretty good. In the sunlight you can see the dust doing the big swirl to the filters.

The price of the squirrel cage was right (free from a neighbours new furnace install) and some old plywood. Plus I have a good table with the sanders on it.

I've noticed a couple times when I changed the filters, there is no dust anywhere in or on the blower housing, so I have myself convinced that I catch most of it.

Plus it's quiet! Easy to fordet and leave on, and since it can move air through a whole house, my small shop is no match for it!

[David Linnabary]

I'm currently planning a squirrel cage air cleaner build that I will be installing inside a section of repurposed kitchen base cabinet, it is mounted on wheels and has a work surface on top. I hope to keep the drawer functional and use it anywhere in the shop as an assembly surface or as needed. I imagine a power strip mounted somewhere and possibly a timer for the fan to shut it off after I've left the shop.

Originally I had thought to just design it as a downdraft table but I don't think I'll go that way.

David

[Dale Murray]

I picked up a 3 speed furnace blower off craigslist for $25 and built a system around it thus creating the most compact system I could for ceiling mounting.

I user three grades of 12x24 filters on the inlet side:
- spun fiber (not shown in photos) for course particulates
- Merv 4
- Merv 7 or 9 for extra fine

I use a spun fiber on the outlet side to diffuse noise from the fan.

Furnace blowers work best when there is considerable constriction on the inlet and outlet pathways. This allows the motor to turn higher RPM while drawing fewer amps thus moving more air more efficiently. Seems counter intuitive but my clamp meter convinced me otherwise.


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This is the exhaust side of the fan prior to installing a baffle to restrict airflow.
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This shows the baffle installed.
I was not sure I would need it until I finished the build. The baffle offers additional restriction muffles the sound a bit.
There is a spun filter on the exhaust side as well. I had not received the filters in the mail at the time I took the photos.
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In this rear (inlet side) with the filter retainer removed to show access to the filters.
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The filter retainer is in place.
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Again, there is a spun filter on the inlet side but now shows in this photo.
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I think I spent between $75-$100 on this entire project and it work beautifully.

[Howard Acheson]

Here is some basic info that may 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.

[Dale Murray]

Cannot argue a single point and will admit I see the most benefit when cleaning up shop.

I do run a DC when running machine with limited exception - that quick cut at the chop saw. When I see the greatest benefit is when I am doing a cleaning at the end of the project; sweeping off tools, counters, and the floors raise a lot of dust and that when the filter really does its job.

[Lee Schierer]

What is the advantage of the squirrel cage fan?

You can get a squirrel cage fan pretty cheap if not for free from a local HVAC contractor. Ask them for an old furnace that they have replaced with a new one due to a heat exchanger crack.

[Ole Anderson]

I used a box fan for years, set up with a cheap 24x24 pre filter followed by a filtrate for the fines. Problem is that with even a little bit of buildup, the fan chokes, it is a high volume, low suction fan. As many others have said, go with a squirrel cage fan. Mine was replaced with a ceiling mount DustRight ambient air cleaner from Rockler, no longer available. Those are typically set up with a pre-filter and a bag style final filter for the fines. And you can really feel the air blowing out of them, unlike the box fans which need to be on hi speed to even spit out any air.

Look at the amp draw of the fan to get a judge of the power. A squirrel cage will provide the suction you need to overcome the resistance of the filters while partially clogged with dust. It is more about overall suction than raw airflow, much like a dust collector.

[Wade Lippman]

Furnace blowers work best when there is considerable constriction on the inlet and outlet pathways. This allows the motor to turn higher RPM while drawing fewer amps thus moving more air more efficiently. Seems counter intuitive but my clamp meter convinced me otherwise.

Yes, it is counter-intuitive. Can you document this claim? Even if true, I would think all those filters would be more than enough constriction.

[Dale Murray]

A. I did some extensive reading to find this information.
B. I was doubtful too until I pulled out my clamp meter and did extensive testing to discover the level of constriction that resulted in lowest amp draw at each speed (I only used the low speed setting in the end).
C. The filters will not offer sufficient resistance to get the optimum in my experience.
D. In the case of my build I found if I only left, as I recall, about 5/8-3/4" on each side of the fan assembly I would get the desired amp draw and increased velocity.

A quick google and I found this. Maybe not the best explanation but will illustrate the point.

http://www.grayfurnaceman.com/blowers-and-fans-design--troubleshoot.html

[David L Morse]

A. I did some extensive reading to find this information.
B. I was doubtful too until I pulled out my clamp meter and did extensive testing to discover the level of constriction that resulted in lowest amp draw at each speed (I only used the low speed setting in the end).
C. The filters will not offer sufficient resistance to get the optimum in my experience.
D. In the case of my build I found if I only left, as I recall, about 5/8-3/4" on each side of the fan assembly I would get the desired amp draw and increased velocity.

A quick google and I found this. Maybe not the best explanation but will illustrate the point.

http://www.grayfurnaceman.com/blowers-and-fans-design--troubleshoot.html


Why would you want to minimize the current draw? Less current means less CFM and longer time to clean the room.

[Dale Murray]

Like I said, counter intuitive.

I just provided links explaining how they work, how they are designed to have restricted flow, and the conclusions of my own tests using a clamp meter on the very motor I used to build mine, I do not intend to make any great efforts to convince you otherwise.

Last attempt:
Some quoted text from http://hvacrfundamentals.blogspot.com/ followed by a link to the article.
Since air is what we work with it makes sense to insure that our students understand airflow and fan performance. Fan motor performance is one of the most often misunderstood aspects air conditioning systems. The amp draw on a centrifugal fan goes down as resistance to airflow is increased. For most people this seems counterintuitive. It is easy to picture the fan motor pushing harder to overcome the resistance and increasing in amp draw. However, this is exactly backwards. Centrifugal fans move air by throwing the air outwards through centrifugal force. The amount of air the fan is moving decreases as the resistance to airflow increases. If the fan blades are moving less air, they can actually spin easier because there is less air to sling. This causes the motor RPM to increase and the motor amp draw to decrease.
http://hvacrfundamentals.blogspot.com/2009/08/understanding-centrifugal-fan-motor.html
(http://hvacrfundamentals.blogspot.com/2009/08/understanding-centrifugal-fan-motor.html)

I would add that when setup correctly you get an optimum airflow/amp draw ratio.
Cut of all air and you get a really low draw but no air movement - thus its a balancing act.

If the link above or the videos earlier have not convinced you then I suggest you get an old furnace blower and do some testing yourself, then you will understand.

And one other bit from the link above:

... operate a centrifugal blower in free air with no restriction and measure both the amp draw and the fan RPM. Note that most centrifugal blowers cannot operate in free air for an extended time without overheating,

The over heating is a result of the heavier load experienced when running in "free air" (without restriction) which increases the amp draw.

[Wade Lippman]

The amp draw on a centrifugal fan goes down as resistance to airflow is increased. For most people this seems counterintuitive. It is easy to picture the fan motor pushing harder to overcome the resistance and increasing in amp draw. However, this is exactly backwards. Centrifugal fans move air by throwing the air outwards through centrifugal force. The amount of air the fan is moving decreases as the resistance to airflow increases. If the fan blades are moving less air, they can actually spin easier because there is less air to sling. This causes the motor RPM to increase and the motor amp draw to decrease.

That is totally intuitive. The more constriction means less air flow means less amp draw. That is the exact opposite of what you are saying.
A DC uses the most current, and moves the most air, when you remove the ducts and filter; and it uses the least current and moves no air when you put something over the intake.

[Art Mann]

Wade is right!

[David L Morse]

Art is right!

[william watts]

That is totally intuitive. The more constriction means less air flow means less amp draw. That is the exact opposite of what you are saying.
A DC uses the most current, and moves the most air, when you remove the ducts and filter; and it uses the least current and moves no air when you put something over the intake.

Dale,Wade, and Art are in agreement. Every one is right. You can prove this for yourself by putting amp meter on your shop vac. Measure the current it draws, then block the intake with your hand, you will see the current decrease. It's not a centrifugal fan, but it's the same principle. Some folks are fooled because the sound from the motor/fan really starts to scream. The rpm increases because there is less air to move, but the current goes down. Dale has fought this battle before.

[Ole Anderson]

The rpm's increase on a shop vac with your hand over the hose largely because the fan is now spinning in a partial vacuum which of course has much less resistance than air at 14.7 psia. Almost like taking the fan off the shaft.

[Dale Murray]

To properly balance a forced air HVAC system you will, among other things, check The Supply Static Pressure (+) and The Return Static Pressure (-) to get the Total External Static Pressure. When adding the two numbers you ignore the -/+, just add the numbers, the is the TESP of the system.

"Most manufacturers’ engineering manuals rate airflow in furnaces, fan coils, and air handlers based on Total External Static Pressure (TESP). A typical furnace is designed to operate at a maximum of .50-in. w.c." (http://contractingbusiness.com/archive/measuring-static-pressure) * w.c. is for Water Column.

If a furnace blower is operating outside those specifications one of two things will happen;
- Zero static pressure (unrestricted airflow) will cause the motor to work harder (moving greater mass than design specifications) thus increasing the amp load on the motor and burning it up.
- Excessive static pressure (near zero airflow) will cause the motor spin faster (the motor is working against nothing) while moving nearly zero air (not enough to cool the motor) and burn up.

In my case my motor told me what the AMP load should be for each speed setting.
I then, using my clamp meter, determined the amount of restriction (restriction of air flow results in Supply Static Pressure as a negative number) required to run at the selected speed with specified AMP load. I then tested at the other speeds and AMP loads to be sure my level of restriction allowed the motor to operate withing design parameters (as specified on the motor).

Whether the static pressure is on the supply side or exhaust side is irrelevant.

So, I guess you can run one of these motors with zero restriction and burn it up, however, you will get optimum performance and air flow when it is operating within design specifications.

I have supplied several links and given enough terminology for anybody to do their own homework and figure this out. If you still have doubts, get a furnace blower and clamp meter and do some testing.

[Dale Murray]

Dale,Wade, and Art are in agreement. Every one is right. You can prove this for yourself by putting amp meter on your shop vac. Measure the current it draws, then block the intake with your hand, you will see the current decrease. It's not a centrifugal fan, but it's the same principle. Some folks are fooled because the sound from the motor/fan really starts to scream. The rpm increases because there is less air to move, but the current goes down. Dale has fought this battle before.

The difference is your shop vac will not burn up if offered unrestricted air flow, most furnace blowers will.

I believe that is the cause of disagreement; the idea furnace blowers are designed to operate with some form of static pressure (supply side or exhaust side), without it the motor will burn up.

[Ray Newman]

"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. "

--Howard Acheson

BINGO! The 1st step to "clean" air is collecting the dust and other particulates at the source.

[Peter Aeschliman]

"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. "

--Howard Acheson

BINGO! The 1st step to "clean" air is collecting the dust and other particulates at the source.

Yep! But this is not to say that we shouldn't also use air cleaners as a backup to get anything that escapes primary dust collection.

[David L Morse]

I believe that is the cause of disagreement; the idea furnace blowers are designed to operate with some form of static pressure (supply side or exhaust side), without it the motor will burn up.

GOT IT! Before you added the restriction your motor was drawing more than it's rated full load current. You then reduced the CFM just enough to bring the motor current down to rated FLA. I couldn't figure out what you meant by "optimum airflow/amp draw ratio". Now I understand that meant maximum flow without frying the motor.

[Dale Murray]

The thing is, the motor was not throwing an impressive amount of air until I restricted it; the velocity increased. Maybe it was the same volume however at a greater velocity.

Think of a squirrel fan as a circle with a bunch of shovels scooping air and the throwing it; that is effectively what it does.
Now lets imagine a hundred men with wheel barrels;
- if you load each barrel with 300lbs they will all be very labored moving dirt and not move very fast and get worn out quickly.
- if you load each barrel with 100lbs of dirt they can nearly jog to the destination and quickly return for more, this will likely improve productivity.

Make sense?

Do not think of these devices like a vacuums or house fans, they are a different beast altogether.

It had my mind bent until I did the actual testing and found it to be true. Unfortunately I dont have my notes from testing where I tracked the amp load.

[Wade Lippman]

There are three claims.
1) Squirrel cage fans will burn out if they don't have enough resistance.
I don't find anything definitive on this, but everyone seems to think it is true; so it probably is.
2) 3 heavy filters don't provide adequate resistance to avoid burning out.
This seems highly unlikely, but I surely haven't tested it, so it might be true.
3) "Furnace blowers work best when there is considerable constriction on the inlet and outlet pathways. This allows the motor to turn higher RPM while drawing fewer amps thus moving more air."
This is just crazy. It might burn out doing it, but an unrestricted fan drawing more current will certainly move more air than a heavily restricted fan. A restricted fan uses less current because it isn't doing anything.

[Dale Murray]

What fascinates me is I have delivered links to professionals stating the very things you doubt.

http://hvacrfundamentals.blogspot.com/2009/08/understanding-centrifugal-fan-motor.html

Since you apparently have not followed or read the links provided, here is the text:

Understanding Centrifugal Fan Motor Performance

Since air is what we work with it makes sense to insure that our students understand airflow and fan performance. Fan motor performance is one of the most often misunderstood aspects air conditioning systems. The amp draw on a centrifugal fan goes down as resistance to airflow is increased. For most people this seems counterintuitive. It is easy to picture the fan motor pushing harder to overcome the resistance and increasing in amp draw. However, this is exactly backwards. Centrifugal fans move air by throwing the air outwards through centrifugal force. The amount of air the fan is moving decreases as the resistance to airflow increases. If the fan blades are moving less air, they can actually spin easier because there is less air to sling. This causes the motor RPM to increase and the motor amp draw to decrease.

The most convincing way to teach this concept is to have students figure it out for themselves using a centrifugal blower. Have them operate a centrifugal blower in free air with no restriction and measure both the amp draw and the fan RPM. Note that most centrifugal blowers cannot operate in free air for an extended time without overheating, so try and keep the free air operating time to a minimum. Next have them block one side of the air intake with a piece of cardboard and recheck the amp draw and RPM. Typically the increase in RPM is immediately obvious, but measurements prove the point. Have them slide the cardboard to block the intake only half way while watching the amp draw. A few minutes of experimentation will convince the students that blocking the intake actually causes an increase in RPM and a decrease in the motor amp draw. Next have them partially block the fan outlet while checking the amp draw. Once again, the amp draw will decrease. Allow them a few minutes of play time to convince themselves. This experiment does more to explain centrifugal blower motor performance than a week’s worth of lectures.

Now that you have them hooked, refer them to Unit 56 Fans and Airflow inFundamentals of HVAC/R where they can read about the characteristics of different type of fans used in the industry and the basic principles of airflow. There the students can see examples of the different types of fans and read about their performance characteristics. Unit 56 Fans and Airflow wraps up with a discussion of the fan laws and using fan perfromance tables and curves. As always, examples show in detail how to apply each of these concepts.


Note that what I have been discussing assumes a "regular" PSC blower motor. ECM blower motors behave differently because they are programmed to adjust their output according to the resistance they are working against, but that is an entirely new discussion which I will save for another article.


Safety note: If you are not sure all of your students understand that it will hurt to put their hands into a moving fan blade, you should put a wire gaurd over the intake and exhaust to keep hands and fingers out. For a more polished trainer build sliding sheet metal baffles for both the intake and exhaust and mount the blower to a stand.




At this time I feel I have delivered enough information and sources. If you continue to have doubts then I suggest you get yourself a blower and do some testing.

[Wade Lippman]

The amount of air the fan is moving decreases as the resistance to airflow increases.
The amount of air the fan is moving decreases as the resistance to airflow increases.
The amount of air the fan is moving decreases as the resistance to airflow increases.
The amount of air the fan is moving decreases as the resistance to airflow increases.
The amount of air the fan is moving decreases as the resistance to airflow increases.
The amount of air the fan is moving decreases as the resistance to airflow increases.
If the fan blades are moving less air, they can actually spin easier because there is less air to sling. This causes the motor RPM to increase and the motor amp draw to decrease.

What part of that can't you understand?!
You have delivered plenty of information; you just don't seem to understand what it is saying.

[Dale Murray]

Put 80" tires on your car and tell me how much faster it is because one revolution of the tire covers a greater distance, never mind your engine and drive train were not designed to deliver that much torque. Most likely you will burn up the engine and transmission and cover very little distance.

You need the torque to overcome the resistance of the large diameter tires.

Put normal sized tires on your car and tell me how much slower your car is because those little tires do not cover as much ground per revolution. Oh, wait. You actually go farther and faster more efficiently because it requires less torque to spin the tires.

Your engine and transmission will spin more revolutions per mile covered but using less torque thus operating more more efficiently.

In the case of a centrifugal fan (from a HVAC system) the lack of static pressure is like putting huge tires on your car.
The fans diameter does not change but the amount of air it is trying to move per revolution is at its maximum. As a result more torque is required to turn the fan and move air. More torque = higher amp draw = more heat = burning up the motor.

By offering a centrifugal fan some form of resistance (in the form of vacuum on the supply side) the fan has less air to push per revolution but is able to spin faster allowing it to push more air.

If you completely block the air flow it will burn up.

[Wade Lippman]

I suspected you were goofing on me. Now I am sure. Okay, you hooked me, but didn't succeed in landing me.

Using documentation that contradicted your point, while claiming it was proof of you point was inspired though.

[Curt Harms]

Perhaps something constructive here - a source for smaller squirrel cage fans. The recycled ones from furnaces are great and typically cheap but sometimes they're a little large, especially if you want to hang it from the ceiling. I have a hanging air cleaner and was looking for replacement blowers just in case. Apparently greenhouses use them - here's one example:

http://www.cheaphydroponics.com/product-p/active465.htm
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I have a similar blower in my air cleaner with a coarse precleaner and bag filter. It seems to work pretty well. If I were doing it again I'd use a furnace filter(s) in place of the bag filter - easier and cheaper to replace.

[Wade Lippman]

Perhaps something constructive here - a source for smaller squirrel cage fans. The recycled ones from furnaces are great and typically cheap but sometimes they're a little large, especially if you want to hang it from the ceiling. I have a hanging air cleaner and was looking for replacement blowers just in case. Apparently greenhouses use them - here's one example:

http://www.cheaphydroponics.com/product-p/active465.htm
322713

I have a similar blower in my air cleaner with a coarse precleaner and bag filter. It seems to work pretty well. If I were doing it again I'd use a furnace filter(s) in place of the bag filter - easier and cheaper to replace.

Grizzly air filters with remotes are only $150. Hard to justify $80 for the fan.