Keeping It Clean: How to Design and Build a Laminar Flow Hood

Keeping mold spores, bacteria, and other nastiness out of your mushroom spawn is a constant fight for the cultivator. You could use a glove box with a pretty high rate of success, but anyone who wants to get serious about growing mushrooms needs to consider using a laminar flow bench.

Having a clean stream of air to work in is way more comfortable and much easier to use than an awkward glove box. A properly constructed laminar flow bench can allow for ultra clean laboratory conditions even in a not so clean environment such as your kitchen or basement, greatly increasing chances of success for a home cultivator.

What is it?

The typical laminar flow cabinet consists of three parts:

  1. A High Efficiency Particulate Air filter (HEPA filter) and pre-filter.
  2. A properly sized blower fan.
  3. A box to hold it all together and and provide a plenum for laminar flow.

The idea is to provide a smooth and constant flow of clean air over a work bench. Working within this flow using proper techniques should allow for petri dishes and spawn jars to be open without risking mold spores or other contaminants getting in.

The end result is easier and more successful inoculations, grain to grain transfers and agar work.

Follow these three steps as a guide to building your flow hood:

STEP 1: Choose a filter

The main consideration when choosing a filter is size. A 12″ x 12″ filter may be okay for home cultivation, but the relatively small size makes it difficult when dealing with large spawn bags or multiple jars. Bigger filters, however, require a more powerful and more expensive fan to push through the required amount of air. A good size filter for at home or small scale commercial cultivation is 12″x 24″ or 18″x 24″ or 24″ x 24″. You want the filter to have an efficiency rating of at least 99.99 % at 0.3 microns. This means that the filter will stop 99.99% of the contaminants sized 0.3 microns or smaller, allowing for a high chance of success.

HEPA Filter For Laminar Flow Hood

Another consideration when choosing a filter is the static pressure. Most HEPA filters will have between 0.8″ and 1.0″ of static pressure (measured in inches of water). This is simply a measure of the amount of friction between the filter media and the air being pushed through the filter. You will also want to add a pre-filter, which is cheaper and easier to replace than a HEPA and will stop big particles from clogging up your filter. It is generally installed at the intake of the blower fan. You can use cut-to-fit vent filters to customize the pre-filter to the size you need. This pre-filter will have a static pressure of 0.1″ to 0.2″, making the total static pressure of the filter system somewhere between 1.0″ and 1.2″. This is actually quite a lot of static pressure and requires an adequately sized fan in order to provide a sufficient stream of clean air over your work area.

The information for both the efficiency and the static pressure of the filter should be provided by the manufacturer. You are unlikely to find this type of HEPA filter locally, however, there are many sources online, offering a number of different sizes. Here is a good one from Amazon, a Novatek filter that measures 24″ x 24″. Or this 24″ x 24″, by Filtration Group is also good choice. If you want to build a smaller filter, you can choose to get a 12″ x 12″ HEPA filter, which may be adequate- albeit just barely- for small scale home cultivation .

NOTE: Make sure you get a proper deep seated filter, such as the ones listed above in order to get smooth laminar flow through the face of the filter. There are cheaper “HEPA” filters, such as the once available for home furnaces – but don’t get these. They will filter the air just fine, but will not produce laminar flow, and thus won’t work for your flow hood.

Blower Fan For Laminar Flow Hood

STEP 2: Size the fan

Laminar flow hoods typically use a squirrel cage type blower fan that is mounted on top of the hood. These fans are rated based on the volume of air that they produce at zero static pressure in cubic feet per minute (CFM). As the static pressure increases, the amount of air the fan can produce decreases. The volume of air that a particular fan can provide at a given static pressure can be shown in a “performance curve” which is usually provided by the manufacturer.

For mushroom cultivation, it is generally suggested that the stream of clean air should flow over the workbench at a speed of 100 feet per minute. This means that the volume of air flow required in CFM can be determined by multiplying the area of the filter by 100 ft/min.

For example, an 18″ x 24″ filter will have an area of : 1.5ft x 2.0ft = 3.0 sqft. Therefore, the volumetric flow rate of clean air required for mycological work is 3.0 sqft x 100 ft/ min = 300 cubic ft / min or 300 CFM. This means we need to find a fan that can provide 300 CFM of air at the static pressure of the HEPA filter and pre-filter combined.

To continue the example, let’s say that the HEPA filter has a static pressure of 0.8″ and the pre-filter has a static pressure of 0.2″, giving a total static pressure of 1.0″. A typical performance curve for blower fans will look like this:

The fan in this example has two speeds, Lo and Hi, as shown in the chart. We can find out the volumetric flow rate of the fan at our static pressure by looking at the curve. As you can see, at 1.0″ of static pressure, this fan should provide a flow rate of 320 CFM at the Hi setting. This is called the working point, and since we required at least 300 CFM, the fan should be adequate.

The fan I ended up using for my laminar flow hood was the Dayton 1TDT8, pictured here. It has two speeds, so you can set your speed depending on the amount of resistance from your flow hood. You can also use the higher speed to scrub the air of your lab quicker. You will need to wire in the fan using a switch. A simple light switch will work just fine.

Dayton also has a number of other fans that are reasonably priced and of good quality. Make sure you can also find the performance curve for your fan. There are a number of good choices at the end of this article.

You don’t want a fan that is too overpowered, but its better to have slightly more flow than not enough. Eventually, the resistance of the filter will increase as it gets dirtier, so having it slightly overpowered should be helpful. If you look hard enough, you should be able to find a fan that will exactly match your filter. Again, these fans might be hard to find locally, but you should have no problem locating one online.

STEP 3: Putting it all together

The final step is to construct a box to hold it all together.

You want the box to have a reasonably sized plenum (enclosed area behind the filter), which acts to pressurize the air evenly over the back of the filter and produce laminar flow.

Laminar flow simply means that the stream of air is moving evenly and consistently across the filter. You do not want turbulent flow, which will cause currents and unpredictable flows that can drag dirty air into your work area. You can check for laminar flow by holding a flame in front of your filter with the fan turned on. The flame should be bent over at a relatively constant angle withing the entire stream of air flow.

These hoods can be made relatively easily if you have the right tools. I was lucky enough to get help from my good friend Jeff over at The Home Stud. He’s got tons of great info on renovations, construction, and even some cool DIY hydroponics set-ups. Be sure to check it out!

The plenum should be 10-12 inches deep, not including the depth of your filter. A good material for the box is finished plywood, at least 5/8″ thick and strong enough to withstand the vibrations caused by the fan. Use silicon to seal the edges, especially between the inside of the box and the filter. You can build a separate box on top to house the fan with a pre-filter on the outside, or simply tape the pre-filter to the intake of the blower. There are many different ways to do this, so choose whatever works best for you.

Build This Same Hood

Wanna make your very own flow hood?

Let me know your email below and I’ll send ’em over to you right away!

This is the full build plans for our 24 x 48″ hood, including all dimensions, all cuts, and everything else you need to know to build you very own flow hood!

Pre-Built Flow Hoods

The cost of the fan, the filter and the plywood can actually get quite expensive. Add in the time and tools required to put it all together and it often makes more sense to buy a pre-built laminar flow hood from a reputable supplier. Without a doubt, the absolute best choice when buying a flow hood is the wonderful folks at Fungi Perfecti. They have a selection of pre-built flow hoods that should meet your needs at good prices. Check out the 24″ x 12″ Series I Laminar Flow Hood here.

Pre-Built Laminar Flow Hood

Staying Clean

Try to keep dust and dirt off the face of your filter. It will be helpful to allow the flow hood to run for an hour or so before use as it will clear the filter of any contaminants that landed on the outside and will scrub the air in the room. Always use proper techniques like trying to keep your hands downstream of the cultures, plates or grain jars that you are opening. Keep rubbing alcohol nearby to wipe down anything that will be entering the clean stream of air. These sterile laboratory techniques will be covered in more depth in another post.

A properly built flow hood will greatly increase your success rate in reducing contamination in mushroom cultivation, and is well worth the effort. If you don’t want to go through the trouble of making the hood, there are completed flow hoods available for purchase online, although they can be expensive and have high shipping costs. We hope to soon provide filters through our store. Feel free to write questions or comments below. Good luck with your flow hood!

author: Tony Shields, FreshCap Mushrooms

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Mikhail Shikhmanov
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Mikhail Shikhmanov

=) great article

Samuel D Phillips
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Samuel D Phillips

I will be making a laminar flow bench this weekend, I like your design. When it comes to a laminar bench does it matter if the filter is 5 7/8″ deep or 12″ deep?… $100 difference not to mention the extra 6″ of room it takes up..

John
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John

Great article! I learned a lot from it today.

I’m trying to put a 24″ X 48″ flow hood, but can’t seem to find the right filter/fan combo. Would you be able to point me in the right direction?

Mr.K
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Mr.K

Hi,
I really like your posts. They are very helpfull to me.
I have a question;
I am using ‘split air conditioners’ to mentain the temperatures.
But, I am unable to decrease the temperature of the room because of the lower voltage. The voltage is about 170 v. and the temperature of my growing room is about 21°C.
What do you suggest me to have lower temperature?
What kind of way should I follow?

Giovanni Fenzi
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Giovanni Fenzi

Hello; Thank you for this wonderful page and i am sorry about my poor english. I want to make my diy laminar flow hood and found a hepa filter. Details of it: Class: H14 / Dimensions: 48″ x 24″ / Initial Pressure Drop: 250PA / Final Pressure Drop: 600PA / Max.Final Pressure Drop: 1000PA. Is it suitable for laminar hood, fungi culture? And if calculate correctly I need blower with capacity 800 cfm flow rate. Is it right? And I didn’t understand pressure calculation on your article. 7667036_orig.png provided by blower manufacturer? Or did you calculate it? Again I am… Read more »

Reid
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Reid

Hi Tony! Thanks for this article! I recently purchased a used Laminar Flow Hood Series I by Fungi Perfecti from a stranger. They claimed to have had little use with it. Currently cleaning the squirrel cage blow fan (it’s a Dayton 1TDT2). The front of the HEPA filter is a tad dusty, with a few scratches. And the rear of it is even dustier. Clearly they got some good use out of it! Being that the HEPA filter is paper material on both sides, do you have any recommendations for cleaning it up? I’ve gently run a vacuum across the… Read more »

Yannis
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Yannis

Hi Tony, great info!
Have you worked with horizontal laminar flow(clean air comes from up the bench)? I must make one for my new room to save space on the bench, what do you think?
Best regards Yannis

Charlie
Guest
Charlie

Hello, I am in the process of getting things in order to build a laminar flow hood. I found a place locally that sells squirrel cage blowers new and used. I would like to build a flow hood that is 24″ x 2 4″ . I spoke to the man who sells blowers with a 450 cfm to 465 cfm with a 120 volt or a 220 volt. I have no idea how many volts I should consider so I said the larger 220 volt would do just fine. Used $50 to $125 new. How much importance is the voltage… Read more »

Heather Z
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Heather Z

Hi Tony! I’m glad to have found your page- you’ve done a great job of breaking this process down and explaining it in a way that is easy to understand and replicate. I noticed you’ve said the HEPA filters should remove 99.99% of particulate at 0.3 microns, but the filters you’ve linked to are described as removing 99.97% at 0.3 microns. In your experience, does this issue impose a significant enough impact on contamination rates to be a cause for concern? I am having some difficulty finding a filter that fits all of the above criteria.

Mateus Pimentel
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Mateus Pimentel

Hello friend i was able to locate a proper hepa h13 filter here with a intital pressure drop of 250pa and a final pressure drop of 600pa, can you help me sizing the fan/blower? how much cfm or m³/h i need before the filter to achieve 100-200 cfm after it? thank you!

Michael Neff
Guest

Hey Tony…wonderful article, well sourced and comprehensive. I’ve done a lot of research on this subject but want to find a unit that is more manageable in size…say 12 X 12″ or 18 X 18.” The Stamets’ basic unit is too much for me to handle and quite expensive. I have zero construction skills and no tools. Have you ever seen anyone market a “kit” that one could just assemble? Even if someone made a kit that only included the basic box, wherein one could then purchase the filter, motor separately. I’m at the point now where Mr. Trich seems… Read more »

Mark
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Mark

Great tutorial and pictures! Have you looked into using a radiator fan which can provide 500-1800 CFM or high output computer fans that can produce 300 CFM? Seems like the latter might work with a 12″x12″ filter. I want to keep things as compact as possible.

Chico
Guest
Chico

I have purchased a Koch biomax HEPA filter with the following dimensions- 24″x24″x11.5″ with the following specifications:
capacity- 1050 cfm
Initial pressure drop- 1.0″ w.g.

I am writing to inquire what capacity cfm shaded pole blower will be sufficient to supply the proper amount of laminar flow to perform my sterile work. Will this model be sufficient:
DAYTON 1TDR9 Blower, 463 cfm, 115V, 1.28A, 1600 rpm

Any assistance you provide will be tremendously appreciated. Thank you very much for your effort and for this excellent article. (:

Jon
Guest
Jon

What filter and fan are you using for your personal flow hood Tony? I trust that yours must perform well.

Jon
Guest
Jon

Where did you find such an odd size? I can’t seem to find anything but 24×24 for that filter.

Jon
Guest
Jon

So would an Astrocell 1 that is 24×24 work with the Dayton 1TDT8 (797 / 549 cfm)? Or would I have to consider another blower?

Thank you so much for your input btw!

GABRIEL HENRIQUE DE LOURENCO PEREIRA
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GABRIEL HENRIQUE DE LOURENCO PEREIRA

NIce article , i’am from Brazil and i am doing my laminar flow hood.
This article was very important to me. In Brazil, its more difficult find a exaust fan and a nice filter. Now, there is a doubt. There are 2 options:
1- Filter 5sqft , need 500cfm , and my exhaust fan Reaches perfect 494CFM in 1.0 static pressure of my filter. Velocity of air clean is 98,8 ft/min.
2- OR 4,275sqft x 100ft/min = 427CFM, my exhuast fan reaches 124ft/min.

What do you recommend? Can this increase in speed hinder the work?

GABRIEL HENRIQUE DE LOURENCO PEREIRA
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GABRIEL HENRIQUE DE LOURENCO PEREIRA

Good night.
I’m from Brazil. Thank you for the answer.
Do you know if the exhausting fan must be on the box. Could i put the exhausting fan on the box but beaside.?

Justin
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Justin

Hello! Thanks for the great article I was going back and forth on forums, this was actually very informative and it cleared a lot of questions. It was a clean cut and dry article. I do have a question though, Is this tough on the electric bill? I mean as far as I know I would only have the flow hood on for a maximum of up to an hour. Do you know any alternatives in fan that will save electricity? Thank you.

Shawn
Guest
Shawn

Hey Tony! I have a 24″x24″x11.5″ HEPA filter (one of the same you linked above), and I am wondering if the Dayton 1TDT8 797/549 CFM is sufficient for that thickness of the filter. And also, is that blower a 110 or 220? Thank you!

Shane Flavell
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Shane Flavell

1160mm x 600mm x 50mm

Shane

Luis
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Luis

HI Tony. I found a 18″ x 24″ x 5-7/8″ 99.97% HEPA filter with capacity of 420 cfm and initial pressure drop of 1.0″wg. Im wondering if the Dayton 1TDT8 797/549 CFM is sufficient for this filter.
Thank you!

Trace
Guest
Trace

Thanks Tony. Love your YouTube videos. Curious about the pre-filter. Is it mounted ahead of the fan, or just ahead of the HEPA filter? If the latter, then an inexpensive furnace filter the same dimensions as the HEPA should work well, I would think.

Geoff
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Geoff

Hello Tony,

I think I bought a HEPA filter too big for this project hoping you can shed some light on whether or not I made a mistake.

I purchased a 24x24x11.5 99.97% HEPA filter with a capacity of 2000 CFM and initial pressure drop of 1.4″wg. Estimating an intake filter at around .2″wg, I believe I need a fan that will produce ~400cfm @ 1.6″ w.g.

The problem I’m having is that I’m not able to find any of these fan performance graphs and it’s turning out to be a little bit frustrating. I was wondering if you could help.

Zoran
Guest
Zoran

Hi Tony

Just planning to build the laminar flow hood using Micron Filter 64cm x 32cm x 15cm and appropriate barrel fan. I want to install it in the opening between two room so I can construct it to suck the air from the adjacent room or from the room into which the clean air will flow.

Based on your experience and understanding, would it of any benefit to have the air flowing from the other room. The work room/area will be quite small and I am planning to put a curtain to separate it from the stairs behind

Cheers, Zoran

Mike
Guest
Mike

Tony,

When you say simply tape the pre-filter to the intake of the blower. What does that look like? From the photo of your set up, I am guessing you cut a square that matches the fan to blow air into the box. Is there a pre-filter between that cut square and the blower?

Thanks

Michael

Loren Fennell
Guest

It appears from your photo, that you are inoculating the Petri dishes in front of the HEPA filter on a metal rack? No inoculating chamber? Something to share from the past… I grew “Roooms” back in the 70’s and built a plywood inoculation chamber box, painted and sealed inside, two holes below a slanted glass window, with long rubber gloves attached to the box. A side door to place quart jars, agar pre sterilized and then, using sterile scalpel and twizers, sliced and diced the culture to the agar. BOOM! In a few days the Petri dishes were covered! Still… Read more »

Phin
Guest
Phin

“Use silicon to seal the edges, especially between the inside of the box and the filter.” Could you give more detail on where to apply silicone between the filter and inside of the box? I can imagine it would be more difficult to replace the filter if the silicone was applied deeper inside the box instead of on the front where the seam between the two would be. I hope that makes sense. Thank you!

Brian Griffin
Guest
Brian Griffin

My filter is 24x18x5.8, (1″w.g.). I fully intend on using a prefilter so static pressure around 1.2″ total. Do i need to compensate for filter getting dirty over time,so instead of a blower that does 300cfm at 1.2″, maybe one that does 350-400cfm at 1.2″? Either way, the dayton 1tdt8 does not look like it can achieve even 300cfm at 1.2″ static. My question is, what is the next size up blower from the 1tdt8 that will put out around 350cfm at 1.2″ static pressure ? Thx in advance

G
Guest
G

Hi, Tony!

You say “deep seated” HEPA filter, otherwise no laminar flow will be produced.
I’ve checked at many filter manufacturers’ sites and they usually offer “deep pleated” and “mini-pleated” HEPAs, the deep being … well … deeper : >=18cm 😉 But yet many promote their mini-pleated series (usually around 8cm thick) as “laminar” while I’ve seen some deep ones promoted as “turbulent”. And they all say mini-pleated is a new technology, allowing for cheaper filters… Do you have any experience with these?
Thank you!

brian
Guest
brian

Can A blower from a central air unit work i definitely think it can provide enough flow its pretty big or is t much flow a bad thing?

Jeremy
Guest
Jeremy

Hi, I just purchased a HEPA filter and the only static pressure provided was 1.4”@250fpm. Do I calculate for this, but add a dimmer to fiddle with the speed when I finish building it?

Fred steadman
Guest
Fred steadman

Amateur mycology has really ruined terminology this is not a laminar flow Hood it is a positive Airway that is HEPA filter which may work but it is not a laminar flow Hood. I worked in labs for the past 25 years and a laminar flow hood is a hood it’s an enclosure with positive airflow that’s HEPA filtered some of them drawdown the equal amount of air that is put in the hood so it doesn’t blow onto your body. But all of them are enclosures typically made from acrylic and aluminum channel

Tim
Guest
Tim

Hi
I have built a nice laminar flow hood using a filter of approx 60cm x 30cm that I aquired from ebay. The filter is new, also looks perfectly clean, but it was just sent in a simple cardboard box without any extra cover. Therefore I am a bit worried that it is probably already contaminated with some mold spores.
Any recommandations how to sterilaize resp. clean the filter? Tought about puting it into the kotchen oven for a while, but unfortunately it is to big.

Josh
Guest
Josh

Hey Tony! This post was fascinating and it seemed to cover every aspect of the science behind laminar flow! I am just starting out and haven’t even attempted my own grow yet. Obviously this seems to be the most expensive part of the whole process when starting out or “up”ing your game in your lab, very similar to my first LED grow light when I started hydroponics. My question is that, am I led to believe that by using a laminar hood, my chances of contaminating a spawn is greatly reduced? Along side other preparatory measures like gloves, wiping down… Read more »

Andrew Newby
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Andrew Newby

Thank you for this in depth description on the specs and details about how and why a flow hood works! It is a valuable asset to have much appreciated and almost all the materials are listed and linked which is invaluable in my opinion.

May someday the soil be valued more than gold!

James harris
Guest
James harris

Hi there Tony. I’m building a 24″ x 32″ laminar flow hood as my 24″ x 12″ Fungi Perfect Series I just isn’t big enough any more. I’m hoping that your plans will be helpful in the construction even though it for a different size. Please send me a copy.
Thanks,
James.

Guy Vaillancourt
Guest
Guy Vaillancourt

Hi Tony,

Thanks for the great article. I would like to know more about building my own flow hood.

Could you send me a copy of your build plans, please?

LISA
Guest
LISA

Can I please get your plans for the 24 x 48 laminar flow hood?

John Alartosky
Guest
John Alartosky

Tony, thank you for sharing all this great info, I’m sure I will have questions, but for now thanks.
John

Larry
Guest
Larry

Nice write up. I will stick to Still air box’s for now, LOL. I’d love a flow hood but I see no reason to get or make one yet as my SAB let’s me to sterile agar work and g2g transfers and also printing caps for spores. Don’t get me wrong tho I’d love a flow hood!

Joe M
Guest
Joe M

Hi Tony. I followed your YouTube channel and I have read most of what you’ve written here on your site. Fantastic and very informative. I have a question. Which blower do you use in you’re 24 x 48 flow hood? I ask because even the big blower you have linked does not provide enough volume at even 1in of water. In fact at 1 in It looks to be about 400. I really want to build this flow hood but need to find the appropriate sized blower. Thanks for all the time you put into answering our stupid questions. 🙄

Love
Guest
Love

I had the same question, but I’m slightly confused. The static pressure of the 5-7/8″depth filter is still 1.0″ IN.W.G.. This is the same as the 12″ AstroCel 1. Doesn’t this mean it will essentially require the same blower?

Thanks for this amazing resource of info by the way!

Chelsea
Guest
Chelsea

I would love to know where you got your 24 x 48 HEPA I can’t find anywhere online so far……..thank you!! These are wonder plans! Bless you guys

Sean R Brosseau
Guest
Sean R Brosseau

Thanks!

Jeremy
Guest
Jeremy

Tony you bloody champion! Thanks for existing, dude 🙂
Would it be at all necessary or beneficial to have walls and a roof on the bench space if you know what i mean? like have the work area enclosed or separated from the space directly above and adjacent to the filter face? or am I just overthinking now?

Stephan
Guest
Stephan

Hi Tony,

Very interesting article.
I plan to build a cabinet where two people can work side by side.
The size would be 2.5 meters wide (sorry metric system).
Should I use one or two blowers?
How about the noise, can I use a noise insulation where the fans are placed?
I want to start a mycelium production here in Namibia, but at a low cost investment for starter.
Later (if necessary) I might go to a more professional system.

Mario Donato
Guest
Mario Donato

Hello Tony, thank you for the tutorial.

I made my calculations, I looks like I need a fan that can perform up to 800CFM, I JUST. OUGHT MY Dayton, but how many CFM has to come “out” of the filter? I didn’t get that part. I’m having scarce 80 CFM after the filtration…

Mario Donato
Guest
Mario Donato

I forgot to mention that my filters are 10 1/2” thick. I don’t know if that influences the results (2x 24x24x10 1/2”).

Jeff Leonhardt
Guest
Jeff Leonhardt

Hi Tony, I built a 24″ x 48″ flow hood using your instructions and the same blower and filter. It was a fun project and I’m eager to put it to use! A quick question: how strong should the air flow be coming out of the filter? I was surprised at how little there was. With the filter out it blows like a hurricane. I know the filter is a major block for the air, but wanted to confirm (for my own piece of mind) that little air flow was expected. If I hold a piece of printer paper up… Read more »

Ronnie
Guest
Ronnie

Who want to sell a 24×24 flow hood