Insulated or rigid duct for fans?

Does anyone know if there’s a big difference in static pressure between insulated flexible duct and say the standard rigid duct available at home improvement stores? Perhaps @Countryboyjvd1971 you can school me here.

I’m asking because I see a stealth grow box in my future. There’s some nice half inch birch plywood that’s going to be leftover from a cabinet I’ll be making. Not a lot, but enough to do maybe a 16”x20”x48” box.

My vision here is to install the fan in bottom of cabinet underneath a false floor that will also have a passive intake and light trap built into it. I found a long narrow carbon filter that I plan on installing vertically in a corner, and then ducting to the fan below the floor. I’m not sure if I’m gonna just exhaust out the bottom of box, or run duct back up and exhaust out the top. So thoughts here are welcome too.

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Well not sure I much help but would like to tag along and learn something.

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@dbrn32 if the run is short, in the range of 9 or 10 feet or less, the flexible duct will be fine. If it is longer then it may be an issue depending upon how many angles and turns are in the run.

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Well there will be at least one 90 degree bend in it. 2-3 if I decide to run it back up to exhaust out the top. I’m leaning against this for space reasons, but not decided either way.

Edit… total height about 48”. The carbon filter is something like 22” long, so if I go from the filter to the fan and directly out bottom wouldn’t be more than probably 2’. If I go back up and out the top, probably about another 48”. @merlin44

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All are welcome to follow, post, or do whatever in my threads. That’s the reason I start most of them haha.

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@dbrn32 To answer your original post. The rigid pipe will have more static pressure. Although, using flexible duct to connect the fan to the rigid duct would keep your static pressures in the (-)negative furthermore. I’m sure you will be fine with flexible duct unless you have a run longer than 25’, then I would suggest using flex from the fan to your rigid pipe. If you are trying to maximize that small space with “out of this world” lights, then venting your air out of the top of the box and out would be the best case scenario.

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Well, you know I will have something up my sleeve for the lights lmao! They will be bright, and hopefully cool. Talking probably 350-500ma 17 volt cobs. But the air will be extracted from near the top either way. I’m just not decided on whether I’m gonna dump it out the top or bottom.

If I understand correctly, you’re saying I will see more pressure drop with rigid duct than with flexible insulated duct?

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Haha I knew you would have the best lights on the market of course why not right! Good choice, how many cobs in that area of 16”x20”? Yeah either way as long as you have your carbon filter or “suction” part of your duct mounted as high as possible in the box, so you can control your temperatures then I don’t see any issue dumping the air out the bottom or the top.

The more I think about it yes, rigid duct will give you more static pressure. The rigidity of the pipe will give the system no drops or sudden surges of high and low pressure.

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That’s more of what I was thinking, but I’m not sure. The flexible sure is easy though. So if I’m only looking at a very small reduction in air movement would be tolerable.

I wouldn’t call them best lights on the market, but very good for application. Fact is I have some heatsinks I’ve been yanking out of scrap ups units at work for the past couple years. They’ll Dissipate about 5-6 thermal watts, so I figure a handful of 8-10 watt cobs would do well. The luminous cxm-9 and Cree cxb1512 both come in 18 volt versions so either of them will keep driver cost down too. Both have 30 degree reflector applications as well, should be plenty of par.

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@dbrn32
Each 90 degree elbow is like adding 2 foot of duct work just a fyi
I agree with @merlin44 a short run go with flex but on a long run rigid pipe would be better and easier to keep straight
As far as static pressure 6 inch flex or ridged would be the same its still only 6 inch

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Yeah just for your purpose of using the flexible duct would be fine, I wouldn’t see much a difference comparing a 10’ run, but having runs as long as 25’ or more then I would start to worry about static pressure drop. :wink::+1:

Those are the perks of a great job! I am hoping to get a gig that will have quirks like that! The luminous cobs compared to Cree give Cree a run for the bank! but the cree are more $ per cob, could you help me out; which has stronger red wavelengths? I would have a leg kicked towards the red spectrum so the plants are short and tight nodes when those buds form; they engulf the stem completely and turn to solid rocks. That’s the goal! :smiling_imp:

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Thank you sir! I’ll probably opt for the flexible and just dump out the bottom.

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To answer your question, per color temp and color rendering index, they’re about the same. So as long as you’re comparing something like 3000k 90 cri from cree to luminous there’s not a huge difference. But if you move to a different color temp and cri in either there could be a significant difference with either of them.

It’s generally blue wavelengths that keep nodes tight. But I’m confident that you can find a spectrum in any of them that will suit your needs. The 50 volt luminous and vero 29 are right there with cxb up to about the 50 watt mark. You start getting above that and the 50 volt cobs are actually better. All a matter of what you wanna do.

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Thanks for that in depth and quick response bro. I get what you are actually saying now! Lol I’m laughing out loud because comparing these leds is like comparing your Chevy to a gmc and so forth. I’m just saying thank you @dbrn32 because without your contributions to the forum and 4 years of college I actually am starting to understand the physics of electricity lol :+1::+1::open_book:

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That’s great! Glad I can help

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When you get to the stealth grow box, I’m in. I’m late, but you got your answers. Do you have a quiet fan for this project selected?
And I need this carbon filter… maybe. Just never know. I might have to be super covertgrower after I move just for a bit. Lol

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Gonna use the 4” ac infinity.

Surprisingly enough, I’ll have very little to buy for it as it sits in my head. I’m sure some stuff will come up, but that’s to be expected. And I’ll throw a few unnecessary but cool items in for sure.

I’ll go see if I can find that filter on amazon and link it. I’m definitely a bit ahead of myself on it, but was kind of trolling the web looking for some ideas at work earlier. Figure if I can grab a few things here and there it won’t hit the checkbook as a noticeable expense. Not to the boss anyway haha!

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It’s definitely not the filter pictured, but the description looks right.

Despite the 125 cfm rating, I seen quite a few reports that the low pro is less restrictive than the shorter filters with higher cfm rating. Either way the smaller diameter will work better for my plans. Pretty sure it will be the one.

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Thanks for sharing @dbrn32 as always. Keep us posted when the box brings forth life!

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Fo shizzle! Will be a bit. I’m planning on using remaining lumber from a fair weather project, but will definitely have a thread.

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