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Tripping2Adventure
StealingKnowledge



Registered: 03/28/16
Posts: 371
Loc: Under a Rock, Bottom of t...
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Flow Hood
#24431448 - 06/24/17 11:42 AM (6 years, 7 months ago) |
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A little while back I purchased two new Grainger HEPA filters, very nice ones. They list for $763 each on the Grainger website, but I got a very nice deal on them (under $300 for both).
My idea was to build a single flow hood with both these filters, and have them side by side. I have the fan to accommodate them both, if I did my math right. The blower fan is a Dayton 1TDU2 model.
The filters have 1.0" of initial static pressure. I plan for .2" for prefilter. That's 1.2" static pressure
The blower pushes out between 850-1000 CFM at 1.2" of static pressure.
The area of one filter (2'X2'= 4ft) times 2 filters (8ft)
The cfm I would need to blow at least 100cfm out the filter is (8ft X100cfm= 800cfm)
So, what I need is a fan the blows at least 800cfm @ 1.2" of static pressure, which I have as stated 3 lines above.
Should I run into any issues running two filters off of one fan in the same box?
I can't find a solid answer (maybe I'm not searching in the right places) on how much depth should be behind the filters? The filter has a 12" depth, so would something like an additional 16" behind that be sufficient enough? Making the total depth of the box to be 28".
The front length of the box will be about 50" to accommodate the filters, and the height will be about 25".
I kind of just wanted to post my ideas so far on this forum so I can get any possible necessary criticism to avoid me from overthinking or missing something completely. Would like to avoid any costly mistakes.
Thanks guys!!
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CapnZ
Dimensional explorer



Registered: 12/22/16
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A lot depends on your design. You will need to make your plenum adequately sized in order to get even air pressure across the filter surface. Are you using prefilters? Need to factor that in also.
-------------------- Deep into the darkness peering, long I stood there wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before...
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: Flow Hood [Re: CapnZ]
#24431660 - 06/24/17 12:57 PM (6 years, 7 months ago) |
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He said he was using prefilters lol
Everything looks good with your math to me
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Boogieman47
Let's boogie


Registered: 03/05/16
Posts: 9,712
Loc: Under your bed
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this is my flowhood 24x24x11.5 why would you want to use 2 12" thick filters ?? One should be good whats the micron%?? ....
I used that tub to bog down the air flow all i really did was build everything up and cut a small hole until the lighter was at about a 65° angle then if it nedds more are i just will cut a bigger hole till i have the same results
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Side by side for a 24x48 work area
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Boogieman47
Let's boogie


Registered: 03/05/16
Posts: 9,712
Loc: Under your bed
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Oh shit haha i misread that i thought he was going to put them behind each other my bad op ...
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CapnZ
Dimensional explorer



Registered: 12/22/16
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Quote:
bodhisatta said: He said he was using prefilters lol
Everything looks good with your math to me
Oops. Missed the prefilter info, but it doesn't look like I was the only one who missed something! Thanks Bod.
-------------------- Deep into the darkness peering, long I stood there wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before...
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CapnZ
Dimensional explorer



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Posts: 1,420
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Re: Flow Hood [Re: CapnZ]
#24431870 - 06/24/17 02:15 PM (6 years, 7 months ago) |
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I have a Dayton blower in mine too. 1 TDT2 (smaller filter than yours). Works great and pretty quiet,
-------------------- Deep into the darkness peering, long I stood there wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before...
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Humble Newcomer
Diddler de niños


Registered: 03/12/17
Posts: 1,483
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Re: Flow Hood [Re: CapnZ]
#24431946 - 06/24/17 02:49 PM (6 years, 7 months ago) |
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While on the subject, is there any truth to the design being absolutely crucial?
I like the OP's % of overengineering he will end with, he could dial down the fan output a little to provide exactly what he calculates he will need, but the fan won't be running at 100% while working day to day, and there is a little room for adjustment.
Surely with solid math like this, and building a square, symmetrical area to be pressurized, there shouldn't be much of a problem.
How much "proprietary engineering" do these flowhood companies have in the angles inside to direct airflow here or there? Pressurize the backside of the filters and it pushes out in a laminar fashion, correct?
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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the plenum doesn't need a special design it just has to be big enough to put even pressure over the back of the filter.
more people have home made flow hoods than bought ones on this site
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Humble Newcomer
Diddler de niños


Registered: 03/12/17
Posts: 1,483
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Thanks for verifying what i see that most build it (and i look forward to the enjoyment of building mine later on).
There was someone on some thread saying the OP needed to include some angled pieces like gussets in the corners at a 45 down to help direct airflow and they had this theory, and since i've never used one it made sense to a noob.
But the more i read the more i think thats bogus.
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CapnZ
Dimensional explorer



Registered: 12/22/16
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Quote:
bodhisatta said: the plenum doesn't need a special design it just has to be big enough to put even pressure over the back of the filter.
more people have home made flow hoods than bought ones on this site 

I did this to my plenum. It's a trick I picked up from a guy with yards of HVAC experience. They charge bib bucks to install something like this in your home HVAC ductwork. It does improve airflow efficiency and minimizes turbulence. This is a pic from the build. The white material is styrene but any bendable plastic or vinyl sheet that's not too flimsy will do.
-------------------- Deep into the darkness peering, long I stood there wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before...
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Humble Newcomer
Diddler de niños


Registered: 03/12/17
Posts: 1,483
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Re: Flow Hood [Re: CapnZ]
#24432505 - 06/24/17 06:33 PM (6 years, 7 months ago) |
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Right on. So a nice long radius 90 like that should suffice, no magic angles to create jfk bullet style airflow
"the angles inside are crucial and thats why its worth paying from fungi perfecti" .... loosely paraphrased, but that's what i read. Not much, but when its the first thing a noob reads, it becomes a seed and grows doubt.
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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they're trying to sell you something over priced.
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c10h12n2o
serial dilutor



Registered: 01/21/15
Posts: 3,200
Loc: the abyss
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right.
op, you might be interested in my flowhood build, it is a lot different than what most people do, its patterned after real ones
i suggest modeling it in 3d first (thats what i did), sketchup is perfect and free
everything looks right to me, but model it first to save time and materials
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  C10's Agar Guide + Tips and Tricks | c10's Flow Hood Build Guide "Partial knowledge is more triumphant than complete knowledge; it takes things to be simpler than they are, and so makes its theory more popular and convincing." "Convictions are more dangerous enemies of truth than lies" ― Friedrich Nietzsche
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hamloaf
Loaf of Fam.


Registered: 12/23/09
Posts: 20,192
Loc: Oklahoma.
Last seen: 1 year, 8 months
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Quote:
bodhisatta said: the plenum doesn't need a special design it just has to be big enough to put even pressure over the back of the filter.
more people have home made flow hoods than bought ones on this site 

The plenum needed to be between 12-24 inches long in order to build static pressure. I went with 24 inches.
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c10h12n2o
serial dilutor



Registered: 01/21/15
Posts: 3,200
Loc: the abyss
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Re: Flow Hood [Re: hamloaf]
#24432744 - 06/24/17 08:06 PM (6 years, 7 months ago) |
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it depends on the area and depth of the filter in question
the point is to provide enough space to equalize the pressure over the filter face to provide laminar flow
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  C10's Agar Guide + Tips and Tricks | c10's Flow Hood Build Guide "Partial knowledge is more triumphant than complete knowledge; it takes things to be simpler than they are, and so makes its theory more popular and convincing." "Convictions are more dangerous enemies of truth than lies" ― Friedrich Nietzsche
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Tripping2Adventure
StealingKnowledge



Registered: 03/28/16
Posts: 371
Loc: Under a Rock, Bottom of t...
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First off, thanks for the plethora of responses everyone.
Quote:
Boogieman47 said:

I used that tub to bog down the air flow all i really did was build everything up and cut a small hole until the lighter was at about a 65° angle then if it needs more are i just will cut a bigger hole till i have the same results
Hey, I like that tub idea to dial it down if need be. Does it make the motor quieter too? And is that restricted airflow harsh on the motor at all? Does it get hot? All the dayton blowers on the Grainger website say they are not recommended for speed controllers, but I see people on here doing it all day long.
Quote:
Boogieman47 said: Oh shit haha i misread that i thought he was going to put them behind each other my bad op ...
I'm not overthinking it that much... lol.
Quote:
bodhisatta said: the plenum doesn't need a special design it just has to be big enough to put even pressure over the back of the filter.
This is what I wanted to confirm. I assumed so based off the lack of information I'm finding in regards to the plenum dimensions. Or maybe because I just figured out the term for the space is 'plenum'?? lol Thank you 
Quote:
CapnZ said:
I did this to my plenum. It's a trick I picked up from a guy with yards of HVAC experience. They charge bib bucks to install something like this in your home HVAC ductwork. It does improve airflow efficiency and minimizes turbulence. This is a pic from the build. The white material is styrene but any bendable plastic or vinyl sheet that's not too flimsy will do.

I had this idea in my head, but didn't want to 'break the tek' and do some unnecessary work that would end up biting me in the ass. I'll definitely implement this in my design. Thanks!  
Quote:
c10h12n2o said: right.
op, you might be interested in my flowhood build, it is a lot different than what most people do, its patterned after real ones
i suggest modeling it in 3d first (thats what i did), sketchup is perfect and free
everything looks right to me, but model it first to save time and materials
I remember looking at your build before I got my filters and fan, I'll have to go give it another look. I did a hand 3D sketch on paper, just don't know any free decent software for doing that stuff on the computer. Not too familiar with all that.
It might be worth putting out here though, I am considering utilizing a fab/metal shop that i have a hook-up with. I had an idea of building this box using a steel frame, having aluminum/ thin steel sheets for the box made with flanges (flanges is not the proper term I'm looking for, drawing a mental blank). The reason I wouldn't want to do this is because it's going to be heavy as fuck. Between the two filters and the blower alone, I have over 100lbs. That's without the box/frame.
Doing a standard plywood board box for this thing would probably be more efficient, but having a metal one fabbed up would be pretty cool IMO. I would post my 3D sketch if I had it with me, but I'm at work.
Thanks for the input!
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hamloaf
Loaf of Fam.


Registered: 12/23/09
Posts: 20,192
Loc: Oklahoma.
Last seen: 1 year, 8 months
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Quote:
c10h12n2o said: it depends on the area and depth of the filter in question
the point is to provide enough space to equalize the pressure over the filter face to provide laminar flow
How deep of a plenum do you think would be good for a 2x4 foot hepa with pre filters?
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c10h12n2o
serial dilutor



Registered: 01/21/15
Posts: 3,200
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Re: Flow Hood [Re: hamloaf]
#24432878 - 06/24/17 09:10 PM (6 years, 7 months ago) |
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thats why i suggested sketchup, its free software from google, easier than anything else, great for laying out cuts, modeling, etc
id definitely consider using a metal fab, but it is by no means necessary. plus, metal is a lot harder to adjust than wood, i wouldnt use metal unless i was 10000% sure about my measurements and had everything modeled in 3d with proper tolerances my buddy bought the massive one from FP and has it hooked up pretty nice, i should post a pic. we mainly use it for tissue culture work though
i got my filter from fp, just to be sure of the dimensions and the arrival date, but i got the blower from cl and built the rest out of wood, sheet aluminum, and plexi. mine is 24x24 and heavy as shit. it has outlets, lights, speed controller, usb quick chargers, etc built in
Quote:
Hamington Loafburg said:
Quote:
c10h12n2o said: it depends on the area and depth of the filter in question
the point is to provide enough space to equalize the pressure over the filter face to provide laminar flow
How deep of a plenum do you think would be good for a 2x4 foot hepa with pre filters?
if im not mistaken, it depends on the thickness of the filter. if the filter is around 6" you need a plenum at least 6" deep. if the filter face is 2x4 ft, i think it just needs to have that same area of 8 sq ft. my filter was just under 6" deep so i used a plenum of 8" and have PERFECT laminar flow from edge to edge.
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  C10's Agar Guide + Tips and Tricks | c10's Flow Hood Build Guide "Partial knowledge is more triumphant than complete knowledge; it takes things to be simpler than they are, and so makes its theory more popular and convincing." "Convictions are more dangerous enemies of truth than lies" ― Friedrich Nietzsche
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Boogieman47
Let's boogie


Registered: 03/05/16
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It does blow hot after running for awhile but i think thats just cause its an old motot from like 1960 haha and it is kinda quiet .. i would get a motor off amazon for sure the 1tdt8 or whatever it is, is a 2 speed and would of been perfect for my filter it was 200$
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Crispykoot
Jello Wrangler



Registered: 10/16/16
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I'm having a cabinet built today for my 2x4 FP hepa. Its going to be 2 feet deep..
FP pairs a 1600CFM fan with this filter which is 2x the needed amount...They have no explanation except. "We sell thousands of these with this fan...It works." I said "Math blah blah blah.." They said: "Silence"...."Send us an email that we will never respond to to answer your question." The ususal.
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Shadowboxing the apocalypse and wandering the land
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spore-ty



Registered: 01/21/16
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I bought one of FP setup and honestly the fan is bit too strong no noticeable contam yet but now I see why they sell a variable speed adjuster lol
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Crispykoot
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Does anybody know if weatherstripping should be used where the filter sits against the furring on the plenum side of the filter?
My filter has weatherstripping on the side that faces the lab.Just seals against the trim...I don't really understand why they are set up that way...
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Shadowboxing the apocalypse and wandering the land
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hamloaf
Loaf of Fam.


Registered: 12/23/09
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Mine has that weather stripping on the side that faces the lab too. I have never heard of weather stripping going along the furring.
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: Flow Hood [Re: hamloaf]
#24433819 - 06/25/17 08:36 AM (6 years, 7 months ago) |
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because the filter is being pushed towards the lab so the weather strip seals the filter to the front of the hood you build that way.
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CapnZ
Dimensional explorer



Registered: 12/22/16
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Quote:
bodhisatta said: because the filter is being pushed towards the lab so the weather strip seals the filter to the front of the hood you build that way.
 The static air pressure forces your filter forward creating a seal against the weather stripping.
-------------------- Deep into the darkness peering, long I stood there wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before...
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Crispykoot
Jello Wrangler



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Re: Flow Hood [Re: CapnZ]
#24433978 - 06/25/17 09:50 AM (6 years, 7 months ago) |
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Makes sense. Everything is going to be caulked really well too. Thanks folks.
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Shadowboxing the apocalypse and wandering the land
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c10h12n2o
serial dilutor



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typically, the weather stripping attached to the filter is supposed to be against the furring
this seal is VERY important on both the lab side and the plenum side, but the part against the furring is absolutely crucial to success
many store-bought hoods do not use the trim sandwich method of securing the filter. my build didnt either, since i patterned it off real ones. i used pins into the filter housing instead of trim to secure it
not only is it important that the weather stripping side be against the furring, ideally it should be TIGHT even compressed against it. i built my pins in a way where they would slant and provide a super tight seal which compressed the weather stripping down a few mm and ensured a perfect seal
the lab side i just secured with plexi silicone, since it was firmly held in place and i was mainly just making sure no air leaked
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  C10's Agar Guide + Tips and Tricks | c10's Flow Hood Build Guide "Partial knowledge is more triumphant than complete knowledge; it takes things to be simpler than they are, and so makes its theory more popular and convincing." "Convictions are more dangerous enemies of truth than lies" ― Friedrich Nietzsche
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Tripping2Adventure
StealingKnowledge



Registered: 03/28/16
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I appreciate everyone's help and advice when i planned this out.
A year or so later, I finally have gotten around to buying the materials to assemble this.
Here's some progress pictures. It is not finished, just functional enough to test.
http://







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Tripping2Adventure
StealingKnowledge



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So... this post is made in regards to testing the unit.
I have not attempted to put a speed controller on the fan yet. I am getting plenty of CFM through the filters... the issue is the flow is uneven
around the edges of the filter has the strongest flow, enough to put a lighter out at some spots... other spots just perfect for mycology work.. and then dead spots in the middle.
Is the issue with my plenum? with the separation of flow in-between the two filters? How should i start diagnosing this issue?
I have a few ideas in my head of the problem and what to do... but I want to hear some voices outside of my own head first.
Thanks again!!
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LizardWizard
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If you ask me, you should have combined the two filter's static pressure plus the prefilter, making for a total of 2.2" static pressure instead of 1.2". Adding to that, if feels to me like you need a deeper plenum with 2 filters. Looking at the depth and width of your filters, I'd go with a twice as deep total plenum.
I'm not sure though, it might be good to wait for someone with more exp to wage in.
IIRC, uneven flow is caused by dirty old filters, weak blowers, or too small plenums, or all of the above.
Again, correct me if I'm wrong, happy to entertain some debate about it and be proven wrong.
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