OK so im gonna build a grow box 3ft square and 7ft high out of mdf. Im gonna use a 4 inch rvk and a 400watt hps. Im gonna have a hole at the top next to the light for the ex fan. Is this the only hole i need though. Someone told me i need holes at the bottom but wont this fuck up the light proof thing. Plz help any info would be greatly sppreciated.Thanks. Pics would be great. sorry for being fussy .

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Yes you will need more holes.
Yes they will have to be light proof.

Good Luck

you could put a hole at the bottom for passive intake. so as the warmer air is vented out, cooler air from outside your growbox is sucked in. why don't you make a hole at the bottom and get some ducting/some kind of pipe attached to it, that'd keep it light proof

[attachmentid=83785][attachmentid=83784]

Hi youll need about 5 times your outtake for passive venting. 5 x 100mm. For light proofing my passive intakes i use square plastic rain guttering see attached picture. You can pick this up at any hardware store. Round gutter pipe os also available but i found square easier to use due to cutting a square hole for the pipe as opposed to a round one. Youll need 2 90 degree bits, either end of a square tube bit. Have the 90 degree bit pionting in opposite directions.

Hope that helps

ok so if i have a hole at the bottom aswell, wont the smell escape even with a carbon filter?

Just get an intake fan .....

Saves all that time pssing about making holes, then light-proofing said holes, then realizing in thius weather you need more holes, then the winter you need less

Get a fan

RAZ

The negative pressure prevents any air / smell escaping from the intakes. Makes sure you seal up with gaffer tape or sealant all inside joins of your grow box. This will help make it more airtight and will also help in keeping it lightproof.

Wait....hang on a minute im confused now, should i make a hole at the bottom or not? Or could i get away with not putting one in. Do i defo need one at the bottom to suck air in to my grow box whilst my rvk sucks air out? Is this right?
How does the smell stay in if theres a hole at the bottom?

If your going the passive intake route, holes at the bottom. Because your extraction fan is sucking air out from the top, it will naturally cause air to be sucked in from your passive intakes. This causes negative pressure. You should have your fans running 24/7 so air will only be getting sucked in from your passives. No air or smell will escape from them.

-->--air sucked in ->- passives ->-- inside of growbox ->-- extraction fan ->-- outside of box----->

So i should have five 100mm holes round the bottom?

Yes 5 x your extraction is the general rule.

so i could four of them 90degree drain corners on the box like in this pic. Im presuming the drain corners come in 100mm? so id use five of them. Sorry bout the basic pic but i think your get the idea. Id have the drain corners in 2 rowsabove eachother. And no smell will escape? Is that right? the veiw will be the side of the box

In my experience I have found passives to underperform, to be honest. You just can't beat having a direct injection system, which also allows for a better light security situation. Just my 5P'worth.

Those 90 degree gutter pipes are 65mm x 65mm. If you choose to use them youll need approx 7.6 of them. So round it up to 7 or 8. If you can find something similar which is 100mm it would be easier for you and mean having to cut less holes.

There are other methods of light baffles which you might consider Click. You could have just the one hole with this method but it would need to be 500mm square.

So long as your fans run 24/7 and more air is extracted than is coming in no smell will escape.

Nice one randomhead,
Got the idea now. Cheers mate.

Been there, done that...I agree

So whats an intake fan then? I was getting an rvk fan anyway so whats an intake fan? is it a different fan?

An intake fan is just that, a fan that takes air into the grow box, rather than taking it out (as an extractor does). I have an inline 4" to suck air straight into my Grow Tent, and an inline 5" to extract the air. The intake is at the bottom of the tent, the extractor at the top. Between them is the oscillator to keep the air stirred inside the tent.

what so instead of buying one rvk i buy 2?

Yes; One as an extractor, one as intake. The Extractor should be an inch or so bigger than the intake, to allow for negative pressure. Negative pressure keeps the smell inside the tent/box until the extractor cleans it on the way out.
Its not essential, but I have found it works better than passive input of fresh air through holes etc. My space is larger than yours, I know. But I would still think that the principle applies, that direct input is best.
At the end of the day, getting the environment inside your growing area right is the single most important thing to be done when setting up a grow. No matter how good the plants are, they will never thrive in a bad environment. Plants need air, loads of it, good and clean and fresh and neither too hot nor too cold.

I know this might sound stupid but what do you do with the rvk to make it suck in instead of blow out? Just turn one the other way round?

Aye that's the one M8, ya just turn it around. So it sucks air into the area, rather than out of it. Of course, remembering to attach some ducting to make a passage between the inside and outside of your area......

So would one of the fans be inside the box and one outside?

Huh? What diff would being in or outside make? You have a fan, and ducting. One end is inside your grow, the other outside. Where you place the fan is really up to you.

Barnzo you really need to do some research, i'm not having a pop but you don't even know the basics of the basics......

Try having a good read through a lot of THIS

Once you've had a good read and there's things you don't understand, come back and post it up here. You'll get a better jist if you read it for yourself....

RAZ