First time grower with 4'x2'x5' tent needs ventilation help

[Dead Cthulhu]

Hello everyone!

I'm getting ready to start my first grow here very shortly and have dialed a lot of things in, one area which i really havent been able to figure out at all is ventilation.

What size fan would I need for a 4x2x5' tent with LED lighting? Would something like a fart fan be my best bet? I'm not really sure what CFM is or how to determine what CFM is needed for what sized area. Also the quieter the fan the better, I'd really prefer something that is, if at all possible, stealthy.

Any help is greatly appreciated!

 

[paul keating]

When it comes to ventilation, you have many options. At the end of the day, it comes down to budget.

But the first thing you need to do is calculate your tent volume.

You quoted it's 4x2x5.
All you do is multiply the 3 numbers to get your volume.

4 x 2 x 5 = 40
Your tent is 40 cubic feet.

When it comes to ventilation, the more the better in my opinion.

When you buy a fan it has a CFM rating. It stands for Cubic Feet per Minute.
It tells you how much air it can move in one minute.

Usually its a good idea to exchange all the air in your grow space once a minute.
So for your tent, i would recommend a fan of at least 40cfm.

However, will you be using a carbon filter?
You need to take that in to consideration. Depending on the fan you plan to use, the carbon filter could reduce your fans air moving capability by as much as 30%, so you would need an even bigger fan.

The type of fan you use will matter a lot aswell.
In my opinion, pc fans aren't very good. I do use them, but only to blow air into the cabinet. They are meant for blowing air, not to overcome pressure, which is what you'll have if you use a carbon filter.

Basically, there are 3 types of fans.

AXIAL: These are really only meant for blowing air, they aren't meant for applications where there may be some resistance, such as the use of ducting or filters. They will perform poorly, and will eventually burn out. I know that from personal experience.

CENTRIFIGAL: These are the fans you want to use. They are meant for high pressure applications, like running through ducting and filters. They will last a while, and do a great job. Though they can be pricey.

MIXFLOW: I'd only heard of these recently, but they are a mix between axial and centrifigal. I'm using one now on my cabinet, and it seems to be doing well. Probably good to start with one of these, if you can't afford a centrifigal fan.

There are lots of options, it all comes down to budget.

Usually an inline fan is required, especially if you are using a filter.
There are some very stealthy fans out there, but they can be pretty expensive.
In the $100's of dollars.

But here's what i would recommend to you.

Your tent is 40 cubic feet, and if you plan on using a carbon filter, i would get a decent fan of at least 80cfm.
So after losses from your filter, you should still get about 50-60cfm, which means your tent air will be replaced every 45 secs or so,
which is good.
Once a minute is a very general rule. The more the better. Especially if heat is going to be a factor.

You said you were using LED's. Depending on what light it is, it can still put out a bit of heat. Not nearly as much as a HID light,
but still enough to cause problems if you don't have decent ventilation.

Let me tell you about my setup.

i have a grow cupboard which is about 35 cubic ft.
My fan is a mixflow, which is capable of about 120cfm.
I have my filter in the corner of the cupboard, going straight out, with the fan connected directly to the filter. No ducting.
The air goes straight into the filter, to the fan, and out.
I'm running a mars II 700w led.
And the air coming out, is usually about 6-8 degress hotter, than when it goes into the cupboard.

I have a few wireless thermometers to check the readings.

I realise my fan should be bigger, but even if my fan is only operating at 25% efficiency,
it still should be replacing the cupboard air about once every minute (roughly),
but i still have a temperature difference of 6-8 degrees.
Which is too much, especially considering it's summer in my part of the world.
But I've found, that most of that heat is contained to the top of the cupboard, above the light.
But without adequate ventilation, that heat will build, and work its way down to the plants.


But that can be a good thing, depending on where you are in the world.
I've seen some people have to run heaters in their tents, because its so cold.
Other people use air conditioners, because its too hot.

So that could be another thing to consider.
The added heat may be beneficial to you, or it could be a major detriment.

You need to change the air to give your plants a steady flow of Co2, of which one change a minute is good,
but if you are experiencing heat problems, you may need to change it several times a minute.

I've heard people say, that the air coming out of your tent, shouldn't be more than 1-2 degrees higher than the air going in.
If it is, you need more ventilation. But like i said, it depends on your situation.

I hope i have offered you some useful advice here.
I've rambled on a bit i know.
I'll shut up now.

Let me know if you have any more questions.

Maybe someone can offer some alternative advice.

 

[Alienpus]

Very nice post Paul, I just wanted to add that for a fan to be able to extract air at it's rated Cfm, there has to be fresh air coming in at the same rate. In a room with no matching fan replenishing the air, the actual Cfm will be lower and determined by how fast the inlets let air in.

 

[Dead Cthulhu]

Thank you Paul! You call it rambling I call it the info I needed to know on making at least a semi informed ventilation choice, that was a huge help!

Would a 120cfm fan work well at dissipating the stank or should I try and find something a little larger? I have an old junk computer i can scrap for 3 fans to use as intake fans. I also plan on making my own carbon filter something like
https://www.-----.com/ic/showthread.php?t=51843
or
https://forum.---------.com/do-yourself/281136-how-cheap-easy-efficient-diy-carbon-scrubber.html
I kind of like the latter more because it isnt some monstrosity and i'd prefer to keep my filter in my tent if thats possible.

Budget wise i'm somewhat limited but I've got a good chunk of things budgeted out

so far I'm looking at $600 max

$60 for my soil and nutes, the soil has dolomite lime and oyster shells, does that remove the need for ph Up and down? Home Grown®: POTting Soil | Doctor Earth This is the soil i will be using as well as nutes from the same brand.
$80 on the tent with free prime shipping
$60 on the seeds w/ shipping
I cant decide if I want to shell out the $ for smart pots or just use the free 2 gallon buckets i can get from work,i could also get free 5 gallon buckets and cut them down to 3 gallon which is the size i think would be optimal for me.
$309 for the lights as i will have to either make two seperate purchases (what I'm doing) or wait an extra week to get started for the 2nd CC to arrive
$10 for a thermo/hygro off amazon
totaled to $519

So right now I'm sitting at $80 bucks left. I could up that and buy some nutes later in the plants life and free up $10 or $20.

What else would I need that I'm missing here, what kind of fans would best fit in that $80 and still allow me to buy the items I havent thought about?

and TY alien thats good to know I think I'm going to try and run some computer fans as intake fans if thats possible

 

[paul keating]

Very nice post Paul, I just wanted to add that for a fan to be able to extract air at it's rated Cfm, there has to be fresh air coming in at the same rate. In a room with no matching fan replenishing the air, the actual Cfm will be lower and determined by how fast the inlets let air in.

Thanks for that.
Yep, you are right. Though fans aren't always necessary, if you are using a passive intake, active exhaust.
As long as your air intake hole/flap is the same size or preferably bigger than your exhaust size, it will still work.
And can be a good thing, if you are paranoid about smells getting out, because it creates a negative pressure area
inside your grow space.
But it will put a bit of extra strain on the fan.

 

[paul keating]

A 120cfm fan should do good for you, as long as heat isn't a big issue. Are you setup yet?
Have you tried running the light to see how much heat it puts out?

I've never tried making a carbon scrubber, so i have no experience or advice on it.
Just make sure you pack the carbon tight. Filter makers use vibrating machines to tightly pack the carbon,
to properly fill every space. Air is like electricity, it will find the path of least resistance, so if you leave a small gap in the carbon, the air will
mostly go through that gap and bypass all the carbon itself, so some smell might get out.

There are several setups you can use for ventilation, but i won't go through them all.
If your going to use PC fans for intake, i would recommend they aren't rated higher (in cfm) than your exhaust.
Using intake fans relieves some pressure on your exhaust fan, but if you are using fans that blow more air into the tent, than your exhaust can suck out of the tent, you will have whats called a positive pressure environment. Which means, more air going in, than going out,
and so that excess air in the tent has to find somewhere to escape, so it will find holes in your tent to get out,
which means smells getting out.


A lot of people use a setup called passive intake, active exhaust, meaning they only use an exhaust, they don't have fans blowing in, all they
usually have is a big hole somewhere for air to get in.
This setup will reduce the efficiency of your fan, but will be constantly sucking air in, through the intake hole and also through any cracks or leak holes in your tent, and will ensure no smells get out. This is called a negative pressure environment.
But you can use an intake fan, a PC fan if you want, just make sure it wont blow more air than your main exhaust fan can suck.

I won't provide any off-site links, because I'm not 100% sure about the rules, but look up the website for
some of these companies.

growershouse
planetnatural
htgsupply

They have some decent, reasonably priced fans.

As for the soil and nutes, I'm not familiar with the brand, but i looked it up, and it's packed full of goodies, that your plants will love,
but i don't recommend using it at first. It's too 'hot' for seedlings. Seedlings don't need any nutrients, and if you use that rich soil, it will stunt their growth, possibly even kill them. I'd start with just some basic potting mix, without any fertilizer, until they have a few sets of leaves,
but that's just my opinion. As for the nutes, again, you won't need them right away.

If it was me, I'd start the seedlings in regular potting mix, until they get a few sets of leaves, then I'd start using a bit of your good soil.
So you could probably go a few weeks before you need to buy any ferts. Assuming you haven't bought any yet.
I'm not sure about the usage of dolomite lime and oyster shells. I have no experience with them, but nothing will remove the need for PH up and down, eventually you will need some. It's good to have them around. PH imbalances can cause a lot of problems, which should be taken care of quickly, so i wouldn't wait until you have a problem to buy them.

For the smart pots, i have no experience with them. But from what i hear, they are pretty good.
Its up to you.
You could always use the free pots for now, and upgrade later if you wanted to save some money in the mean time.

It looks like you are on track with your setup.
I can't really think of anything else you might need.

If you haven't discovered it already, there is a good area to go to for information.
Its in the menu at the top of the page, labelled as 'grow room', and then go to 'how to grow marijuana'

Heres the link to it.

How to Grow Marijuana Everything You Need to Know

 

[Alienpus]

Passive intake all the way the tents already have the vents. I hope I didn't come off as suggesting an intake fan. FWIW save up the 140$ for a 4" fan/filter combo, at least you know it will work.

 

[Dead Cthulhu]

I'm not set up yet, I have 2 $300 credit cards with 0%interest in the mail I was hoping the first would arrive here today but it looks like i'll have to wait until monday. I'll buy my first mars hydro 300w old model, tent, seeds, soil and fan when i get that and can figure it out a bit. I'm planning on running 3 mars 300w old model's. i was going to do two but someone said it'd be somewhere in the realm of a 25-33% increase in yield with the 3rd light. Would 3 of those lights put out a lot of heat? is that also a reasonable yield boost from the extra light?

I'll check out those places for vents, i think i looked at HTg though and all theres were $60+ i think, i'll look again, worst case scenario I go with a 120 off amazon i can get one for 20-30 bucks, hopefully it wont burn out in one grow and i can upgrade later.

As for the intake fans, if i don't need them, I'm fine without.

I've heard auto's really dont like to be transplanted and i see a lot of the really big Fast and Vast plants i've found in grow journals seem to have been planted directly to soil, if i filled a bucket mostly with the POTting soil and then found some not very nutrient rich soil could i make like a small well of the meh soil in the hot soil and not burn the plant, or would it probably be better to transplant them?

I actually just found that today but skimming over it i saw most of the lighting threads dealing with HID's and not much LED coverage and no autoflower section, though i really didnt look super closely just skimmed all the threads

 

[paul keating]

I've heard the old models are cool running, so they should be ok.
Are you going to be able to fit those 3 lights in that space? Might be a little tight. And even with cool running lights, in that tight space, close together, they might produce a decent bit of heat. Sorry, i can't tell you that for sure. Just a guess.
The lights will pay for themselves eventually in extra yield. I couldn't give you a percentage. I'm not experienced enough, and am still growing in a small cupboard with a single light. lol.

Me personally, i would recommend spending the money for a decent fan.
I tried the cheap little axial fan, and it didn't perform well, was noisy and it was made of plastic, and eventually the motor melted through the plastic. So it must of been under some stress.
I'm trying out a mixed flow fan at the moment. had it for about 3 months, seems to be doing very well, pulls a decent amount of air.
But looking back, i wish i had of spent the money upfront on a decent fan.
It would of been cheaper in the long run.
I've tried to do everything on the cheap from the start, and it hasn't worked out well.
I heard a good saying in these forums recently; 'if you buy cheap, you buy twice'.
But i realize you are on a budget. Just thought I'd share my personal experience.

I was always worried about stealth, i didn't want a noisy fan. But if you spend decent money, get a high CFM fan with a speed controller on it, you can lower the speed of the fan, which considerably quietens it.
I would do without an intake fan. I actually do use one on my cupboard at the moment, but it's only a little PC fan,
and it has a low CFM rating. I just use it to take some stress off my exhaust.

I haven't tried autos yet. I prefer to have complete control over them, and when they flower.
So i can't give you any advice. I don't know about whether they can be transplanted or not.
But what you could do, is fill most of the pot with your good soil, but in the middle at the top, just put a bit of regular soil, about the size of a coke can roughly, and plant or put your seed there. So it only has regular soil at first, but as the roots grow, they will grow out into the good soil.

 

[Dead Cthulhu]

Oh yeah, the lights would fit fine, altogether they are only 15.7"x24.9" so thats no problem.

I was looking at photo plants for a while but I came across Fast and Vast which has some pretty crazy yields and potency and I figured why not, As long as i can get 1oz a plant, I could pay off the grow in 2 months of savings from not buying off the street, which some grow journals have people getting 4-5oz a plant and the lowest i can remember seeing is like 40g a plant. The prospect of high THC bud faster was a big draw, I'll probably try some regular plants sooner or later though.

Thats actually exactly what i meant! just worded much better lol, ty for your help