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OfflineLa Flama Blanca
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Flowhood help, Plz no h8
    #23464140 - 07/21/16 09:48 PM (7 years, 7 months ago)

I know you guys must be sick of these treads but I am remarkably skilled at fucking up things when I try to wing it and I really don't want to waste hundreds of dollars. Before I buy this filter and this blower to build my flowhood, I just want to make sure of a couple things;

-is this filter too thin? I know that 5-7 inch deep is what's recommended (idk why though) so will a 4.25 inch depth work or no? It's also 22 inch by 22 inch (L*W)so that's awkward too, though I don't see why it'd be a deal breaker.

-the blower specs on grainger seem to only go up to .8 SP...and from what I understand, our flowhoods are often times 1.2 SP due to the pre filter's SP or something. Since I need 325 CFM for this filter to have laminar flow (1.8ft*1.8ft=3.25) and this blower delivers 360cfm at .8 that should be acceptable if my SP is .8 but perhaps not if my SP is 1.2, so then I'd be screwed. How do I know what my SP will be? Surely it must depend many factors (the rooms RH, filter thickness, how clean my filter is, ect ect). I must be misunderstanding something....

Any other thoughts are much appropriated, too. I.e., Shitty choice in filter material, blower too big/small, wrong gasket type on filter, ect ect. Please help me not waste a ton of money!! :crazy:

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Invisibleweetsie
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23464234 - 07/21/16 10:11 PM (7 years, 7 months ago)

That filter is only 0.48w.g, you want double that ideally. the 1.2 figure will typically be 1w.g from your hepa and 0.2w.g from your pre filter.

Edit: My filter is 6" /P = 0.6w.g so not much better in terms of specification yet has worked flawlessly for many years, I use an over rated fan with on a dimmer switch which I turn up until I get laminar flow. I would still look for a more suitable filter.

Edited by weetsie (07/21/16 10:21 PM)

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Offlineleschampignons
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23464266 - 07/21/16 10:19 PM (7 years, 7 months ago)

I just made a hood with a 4-5" filter and it is working fine for me. Other people have done it as well I believe. The worry is that with a thin filter you will not create proper laminar flow, but in reality I think this turns out to not be the case.

the total static pressure is the sum of the static pressure of your filter + the static pressure of the prefilter. In the case of the filter you linked, it only has a static pressure of 0.48. The static pressure of your prefilter depends on what you use as a prefilter. It probably won't be more than half the static pressure of your actual filter (0.24 in this case). so at most you are dealing with around 0.72" of static pressure or thereabouts (because 0.48+0.24= 0.72)

if your static pressure ends up being too high, you can use a thinner prefilter (within reason ofc because you still want your prefilter to work as a prefilter.)


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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: leschampignons]
    #23465015 - 07/22/16 06:47 AM (7 years, 7 months ago)

Hmmm I see. Maybe I should just bite the bullet and get one of the ones of FP. More expensive but I'd have peace of mind...

edit: would this filter work with that same blower, the dayton 1tdt2?

Edited by La Flama Blanca (07/22/16 08:17 AM)

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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23465556 - 07/22/16 10:25 AM (7 years, 7 months ago)

I decided to buy the 24x18 filter on fungi perfecti...it has a SP of 1".  looks like i need a stronger blower now since it needs 300 CFM pressure at 1.2 for liminar flow. i cant seem to find one on amazon or grainger. can someone help me find one please?

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Offlineleschampignons
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23465564 - 07/22/16 10:28 AM (7 years, 7 months ago)

The ones on FP don't even list the static pressure, so you can't match the filter properly to the fan. I remember looking when I was building my hood at these filters and this fact was infuriating... still is lol

Edit: how did you find out the SP? did you call FP?


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Offlineleschampignons
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23465569 - 07/22/16 10:32 AM (7 years, 7 months ago)

this was the same problem I was having when I was trying to match my blower and filter. Here's my thread discussing the fact that I can't find a big enough blower.

It's also in my journal in a link inside flowhood build thread


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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: leschampignons]
    #23465583 - 07/22/16 10:36 AM (7 years, 7 months ago)

yes, i called FP and the lady told me it's rated at 1"

thanks for that linK! thats exactly what i need. reading now.

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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23465610 - 07/22/16 10:50 AM (7 years, 7 months ago)

hmmm that wasn't as helpful as i was hoping lol.

what do you think of this blower?

or this one?

they seem too affordable... too good to be true... 720-790 CFM, the 8" is less than 100 bucks!?!

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Invisibleweetsie
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23465637 - 07/22/16 11:04 AM (7 years, 7 months ago)

Ask for the model number and try to find a data sheet. They should contain a graph showing the air they move at different levels of resistance.


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Offlineleschampignons
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23465652 - 07/22/16 11:12 AM (7 years, 7 months ago)

I think those CFM ratings are for the fan by itself. when you start adding static pressure, the CFMs drop, and not necessarily in a linear fashion. Link to an example blower. You can see the CFM's drop as the SP increases.

So while those fans might be able to output 720 CFM with nothing to push against but air, that definitely doesn't mean they can push 720 CFM at 1", and it may not even mean they can push 300 CFM at 1"

Interestingly, the 10" fan says the 720CFM number is a "loaded" spec rather than "unloaded" like their competitor. But the question is loaded with what? 0.1"SP?.....3" SP?... It's like saying I can run a mile in 7 mins with a loaded backpack  - loaded with what? feathers? bricks? depleted uranium? This already makes me question the quality. Many blowers will have a chart with the CFM at different SP's like the one I linked above so you can match filter to blower.



Edit: did you ask the FP staff what CFM the 1" SP value corresponds to? 1" SP at what CFM?


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Edited by leschampignons (07/22/16 11:49 AM)

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Offlinejoshxjosh
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Re: Flowhood help, Plz no h8 [Re: leschampignons]
    #23465997 - 07/22/16 01:03 PM (7 years, 7 months ago)

I contacted FP also and they gave me this spec sheet

http://imgur.com/pzWGrGN

Edited by joshxjosh (07/22/16 01:03 PM)

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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: joshxjosh]
    #23466104 - 07/22/16 01:46 PM (7 years, 7 months ago)

didn't know SP could change at different CFMs...so it's basically a moving target trying to figure that shit out....holy fuck this is so much more confusing than i thought it would be. :mad2:

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Offlineleschampignons
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23466161 - 07/22/16 02:04 PM (7 years, 7 months ago)

ok so we have 1" SP at 429 CFM for your filter.

What you want to do now is find a chart (or graph) for a blower which delivers 429CFM at 1". I looked a bit but haven't been able to find one, but perhaps if you call a blower supply asking for that. Or you could use an oversized blower and knock it down with a dimmer switch.


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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: leschampignons]
    #23466186 - 07/22/16 02:11 PM (7 years, 7 months ago)

I thought i needed 300 CFM at 1" for that filter??? Because 1.5ft*2ft=3ft so 300CFM for laminar flow at 1"....or 1.2" if I use a prefilter. am i wrong?

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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23466594 - 07/22/16 04:11 PM (7 years, 7 months ago)

yes you need "at least" 300 CFM to achieve proper laminar flow. The point at which this filter has been tested/ designed to work is somewhat above that.

"According to Stamets (Paul Stamets and J.S.Chilton: The Mushroom Cultivator p. 347 ff) the air speed of the air flowing from the filter surface should be (at least) 100 feet per minute(fpm).(around 30 meter per minute or 0.5 meter per second)."

from this helpful link which you prob have already read


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OfflineLa Flama Blanca
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Re: Flowhood help, Plz no h8 [Re: leschampignons]
    #23466639 - 07/22/16 04:22 PM (7 years, 7 months ago)

yes of course i read that page several times already, but in the other recent post by you, you said i infact need 429 CFM at 1, not 300 CFM(which should be adjusted upwards by 10-20%). thats why i was confused. thats more than 30% overpowered which would be too much, according to that same tek

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Offlineleschampignons
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Re: Flowhood help, Plz no h8 [Re: La Flama Blanca]
    #23466728 - 07/22/16 04:58 PM (7 years, 7 months ago)

Oh I see on the fungifun page where it says not to go above 20%. I'm not sure why that is the recommended rule.

There are two separate conditions we are trying to satisfy.

First, Simply get good laminar flow at 100CFM, which is satisfied anytime you get over 300CFM

Second, match the blower to the filters resistance .

The 24x18 filter is rated at 429 (as joshxjosh pointed out), meaning that it has had its resistance + penetration tested at 429, and we can therefore assume this is the CFM it's designed to be run at. You could run it at a lower CFM, but as Terry M pointed out in the thread I linked, when you put less CFM the resistance that the filter offers changes (it drops).


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