Thanks for the information. I now have negative pressure with a 6" exhaust fan rated at 440cfm. I have two 6" inlets near the bottom of the tent. No inlet fans. My temp at the bottom of the tent where my seedlings are is 84F.
I’m thinking that I’ll add an Intake Fan like
Any other suggestions would be appreciated.
F
That should work out fine I would get a speed controller as well the sell them for a few bucks $20 maybe as well on Amazon gives you options to run full speed or 1/2 - 1/4
What size is the tent your working with @garberfc
440 cfm is a lot of air
Also what the temp In room tent is located in and type of light your running
The tent size is 4x4x80, the outer room is kept at 75F with a window A/C unit. I have one light, a NextLight 525w 
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The light is currently 48" above the floor of the tent.
Ok so you have just over 100cubic feet of space in that tent with your exhaust fan going your exchanging air 4 times a minute imo thats too fast I would slow it down to at least 1/2 and still put that intake fan in should make it easier to maintain temps and humidity levels as wel
run that at around 100 cfm f running your exhaust at 200 cfm 
That looks light looks really nice my friend did a quick glance at the link
I wish I knew how many actual CFM I’m getting verses what the fan can do without the filter and ducts. Yeah, I have big hopes for the light. I hope to see lots of growth/buds in my future 
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F
There’s a lot of bad ratings for most all the 6" duct fans! Can you recommend any brand names?
This is all I use for my intake, cheap, but works like a charm. And fits right into that duct on the bottom of the tent…
But I grow autos, so light leaks are not so much an issue for me…
I’ll be honest with you I get my fans from a supply house I use at work you can get them in Amazon as well but I’m drawing a blank right now on the name
I’ll get it for you when I get home
I run 100 cfm wxhaust fans in my 4x4x7 tents ?
Looks loke you could take the stand off and slide that right in any duct, in-line too
I’d be interested too.
If I read that right, you’re using a 100 cfm fan to exhaust, is that with a carbon filter?
That’s right @dbrn32 with carbon filters I have three setups just the same 4 inch inline fans with carbon filters andnits more than enough to keep my tents air exchanged I also run a carbon filter on my exhaust for the grow room as well
It’s not about moving more air but the right amount ans replacing it with the right amount
Most of the post I see where people are havingbissue especially when running leds is because of over sized exhaust fan set ups
I agree with having the right amount, and there being such a thing as too much exhaust. That’s pretty much the reason I was asking.
The biggest deal I have had is with most fans not being compatible with the typical speed controllers. About the only success I’ve had is using a variac, or the DC mixed flow type fans. Anything else and you usually start to create a whine in the fan motor below about 70%. It’s really annoying!
We tinkered with trying to get small enough fans that only needed to be reduced by 10-20%. And supplementing intake air. There’s just too much swing in the seasons here in midwest to do that. You end up having to leave that range in one season or the other. Or fighting temp issues or humidity the opposite.
Even when budget isn’t an issue per se, it seems like there are limited options for smaller grows. When you start increasing the size of your grow, a/c and large humidifiers and dehumidifiers become better options, but that’s all in place of giving up grow area. Since every are is a little different, ducting and filters can really change things quickly. There’s definitely an art to matching things up that I’ve yet to find.
I understand your background is in the hvac field. If you don’t mind taking the time, I’d love for you to share how your system works and what you’re using.
As a side note, I don’t believe that ventilation issues are limited to led grows. I think it’s more of a shift in the amount if new growers using led over hid. The handful of growers I know that have switched claim that their atmosphere is much easier to control under led lightning. Perhaps as you suggested, maybe too easy and a different approach was needed. At any rate, we can probably equate that to experience more than anything else.
Thanks!
wait
why exactly would too much airflow be a bad thing?
Efficiency for one. Anything more than needed is essentially a waste of electricity.
I think what countryboy was eluding to with the led’s was the difference in canopy temps as opposed to hid lighting. I’m not exactly sure if it applies to everyone, but the majority of heat in led grows isn’t put on the canopy like say an hps bulb. So in an instance where you’re drawing cool enough air, too much could have a negative impact on your grow.
I suppose an extreme negative pressure situation could also cause the possibility of contaminates to enter your grow area through seams or leaks, and is probably hard on tents too.
I’m far from a professional, but I’ve put together a few systems. Had my butt kicked plenty too!
@Countryboyjvd1971 - Did you have the chance to see who’s the manufacturer of the inlet fan?
I won’t lie @garberfc I did forget to do it ladt night
I just check with my supply house tho they are made buy a company called fan tech the vine is all different sizes you may even be able to get them at the big orange box stores online
I use 100 cfm 4 inch fans they are a little under sized for my tents but I still exchange my air ever 1.5 mins and that more than enough for me
@dbrn32 your ex aptly right are far as led light la that was what I was referring too and also on point as far as efficiency also it hard to maintain humidity when your pulling all the air right out of tent
For those using Hps or MH light a vented hood should be used to as well as a exhaust to properly maintain tent temps
My set up is in my basement I run a Ac maybe 5-7 days a year and a dehumidifier the rest of the time I maintain my tents in a range of 72
82with my light running
You’re right @Countryboyjvd1971, I wasn’t thinking about humidity. Especially when you consider the costs of running a/c or a big dehumidifier, doesn’t make sense at all to be pulling air out rapidly. And thanks for the reply!
I will definitely check those fans out too! Have you had any of the issues I mentioned running them with the cheap speed controller? I believe most of them are considered rheostats? Like I mentioned before, I haven’t really had any luck with them. There’s always the annoying noise below a certain range and/or premature fan failure. I’ve settled on using a variac for larger applications, and mixed flow dc fans for smaller. If there’s a cheaper option without those symptoms, I’ll start recommending them instead.
While I’m bugging the snot out of you, do you have any experience with the Ac infinity fans? I think they are relatively new, and came up through electronics cooling devices. I’ll post a link for a fan I just picked up. Basically, it’s 4" 190 cfm duct style inline fan. Amazon price was $99, but it comes with clamps, mounting hardware, and more importantly a contoller. The controller has basic speed and temp control modes, and a smart mode as well. In smart mode the fan will adjust it’s speed based off the included temp probes reading. Manufacturer has them rated at 15 watts abd 28 decibels, which I’m sure is at lowest speed, but still pretty good I think.
Plan is to install it in a 48"x32"x60" cabinet I’ve been working on. I was planning on installing it passively and using the smart mode. What are your thoughts? I have a 6" hyperfan that I can reduce to 35% of 390 cfm that I used in a much larger area, but times have changed and that space had to be used for something else.
I really appreciate the help, thanks!
@dbrn32 I’ll do some numbers crunching in a little bit you I’m at work and at the moment I’m completing my rounds I’ll have a few minutes in a hour or so
I’ll definitely get back to you
Truth is I run mine full sped all the time no need for a speed controller cause I sized my set up correctly
Thanks! It’s about 55 cubic feet. I’m not sure how it will deal with the static pressure of the filter, but I figured after the filter and hopefully it wouldn’t be running more then 50-75%, that I would end up between 1-2 exchanges per minute?
Ok let me think about this you may be better off with a small room to room fan or duct fan in that case which would cost less actually I’ll look a few things up for consideration bro
How far of a run you going to outside?
