Almost finished grow room but I need your help!

[weatherboxes]

Hey guys Im brand new to the website so I guess it is nice to meet you all!?

Ok so heres the basics of my grow box:
Dimensions: It is 5ft H x 4ft L x 3ft W. A total of 60 cubic feet and 12 square feet at its base.
Lighting: 400 watt Mh & 400 watt Hps w/ yield master II hood & 400-1000 watt digital ballast.
Ventilation: Exhaust runs from the hood to the top with a 4 inch can fan (173cfm). I also have one oscillating fan at the bottum (see picture).
The box is pretty much light proof and is completely lined with mylar/white paint.

So here is my question: As far as air intake goes I can either drill 2 inch holes or 4 inch holes. Im guessing because of the negative pressure I wont need an intake fan. I was thinking of putting the intake hole on the opposite side of where the exhaust is and low down by the plant's canopies. Any suggestions to the size/number of intake holes I should drill? All suggestions are much appreciated. THANK YOU!!


PS: My seedlings are growing strong expect a journal soon.

Here is a picture of my grow apparatus thus far:

 

[FreezerBoy]

Easy answer is two intakes per exhaust. All the same size.

At 12 sq ft, a 400 is a bit small (34 wsf) A 600 would be perfect (50 wsf) or you could keep the grow around 3X2.5.

 

[weatherboxes]

As much as I want to take your word for it and run down and drill two 4 inch holes in my box; I shall wait and analyze the inevitable conflicting information. Thank you so much freezerboy! As far as the wattage for my bulbs go I am going to stick with the 400watt for now.. I will only be scrog-ing 2 plants with a 2x2/3x3 screen.

 

[FreezerBoy]

Please, analyze away. As I said, it's the easy answer. There are formulas for those who care to be exact. FWIW, I have dual 4" intakes for my single 4" exhaust and my fan ramps up and down every time I close or open the door respectively. I'd be running 3X except my freezer is two layers of steel and a pain to cut.

fan-intake calculator

Ventilation 101

 

[weatherboxes]

Please, analyze away. As I said, it's the easy answer. There are formulas for those who care to be exact. FWIW, I have dual 4" intakes for my single 4" exhaust and my fan ramps up and down every time I close or open the door respectively. I'd be running 3X except my freezer is two layers of steel and a pain to cut.

fan-intake calculator

Ventilation 101

i see how 4 inch intake hole for a 4 inch exhaust would work but wouldnt two 4 inch intake holes negate the negative pressure creating positive pressure? keep in mind these intakes are passive and just big holes.

 

[shrooom]

How about making three maybe four holes, then you can adjust the intake by blocking the holes.

 

[bongoie]

i'd say freezerboy is making sense . pro looking room u have ere . u can use a filter on the passive intake , something like cooker hood lining , however having the exaust on 24H will stop the smel in flower . advice given to me but never taken is to place the fan up stream of the bulb/tube as the heat can reduce the working life of the fan motor / ur's looks awfy close to the hood , whot's ur wattage ? hope this helps // edit , 1K that'll get hot weatherboxes

 

[Aerohead]

i see how 4 inch intake hole for a 4 inch exhaust would work but wouldnt two 4 inch intake holes negate the negative pressure creating positive pressure? keep in mind these intakes are passive and just big holes.

I don't believe you can create positive pressure with any number of passive intake holes. You would have to have intake fans to create a positive load in that box. Listen to Freezerboy, go with more intake holes than you think you need, it will let your exhaust fan run at peak airflow.

 

[Aerohead]

Another example of Freezerboys experience, I have an 80CFM fan exhausting a PC case with 2 3X5 inch intakes and I can hear the blower fall under a slight load when replacing the side panel to the case.

 

[fishheadbob]

Freezer Boy most always gets it right. Skip the analyzing, follow his lead.

 

[boston]

i have a 4x8 w 6" vortex exhaust and a 8" passive intake
i just added 2 4"

more=better air flow

and negtive airflow still wants to rip poly off walls

 

[weatherboxes]

i'd say freezerboy is making sense . pro looking room u have ere . u can use a filter on the passive intake , something like cooker hood lining , however having the exaust on 24H will stop the smel in flower . advice given to me but never taken is to place the fan up stream of the bulb/tube as the heat can reduce the working life of the fan motor / ur's looks awfy close to the hood , whot's ur wattage ? hope this helps // edit , 1K that'll get hot weatherboxes

hahah yeahh its only 400 watt right now i was just stating i have the capability of upgrading to 1000.. which the box is wayyy to small for. good looking out though.


alright guys im going to drill my holes today.. thank you all for your input. i didnt know freezerboy was the authority on ventilation. it seems as though you are all in agreement with him. you have to understand this is my first growbox/grow ever so im just really trying to make sure im getting it right. HAPPY HOLIDAYS BY THE WAY!! BURN ONE DOWN!

 

[FreezerBoy]

i see how 4 inch intake hole for a 4 inch exhaust would work but wouldnt two 4 inch intake holes negate the negative pressure creating positive pressure? keep in mind these intakes are passive and just big holes.

Negative pressure comes from airflow; The more airflow, the less pressure. It's why airplanes fly but, only after they get up to speed. Within reason (some here use 4X intakes) the more intake holes the better with the worst case scenario being neutral pressure. You want as little restriction as possible and all of it at the entrance. Lack of restriction eliminates airflow and provides neutral pressure.

Fans cannot pump out more than they suck in but, they CAN pump in more than they suck out. That's positive pressure. Air backs up at the exit and airflow slows, pressure climbs, escaping air is forced to bypass the resistance of the filter. Never let the exit be the bottleneck.

2X passive intakes is "Venting for dummies." You can do with less, run formulas, add intake fans but, you need to know your stuff. Or, you can take the easy way out; Punch 3 holes and be done.

If you want guys who actually KNOW how it all works, try redgreenery (of ventilation 101 fame) or HoosierDaddy. Me? I'm a dummy, I take the easy way.

 

[weatherboxes]

i went ahead and drilled one 4 inch passive intake and the negative pressure seems decent right now. the mylar is lifting a little around the hole. however, i dont have a indoor temp/humidity at the moment so my temperature is all by feel. i think i will drill the other 4 inch passive intake making two. i'll make that decision after i buy something to monitor the temp tomorrow. thanks fridge this exhaust and intake thing seems like it could get really complicated and out of hand and who doesnt like the easy way? haha.

 

[weatherboxes]

now im having electrical problems.. both sockets are 15 amps and should have no problem running a 70w can fan and 400w mh or hps.. but when i plug them both in and turn one off the light will not turn on again.. gotta talk to my local hydro store tomorrow. i will not be defeated!

 

[bongoie]

weatherboxes they digital/electronic ballast {thats not starting ? } U gotta leave them a few mins before firing them up again / try this+hope it helps .. ur on the right road to sucsess my friend , yea the intake extract can get baffling / seems u might have it susses now tho . i agree with freezer boy a 600 would b nice in ur room or the 2x400 MH+HPS mixed lighting / or the 1K blowing air straight through the hood and out of the growroom . the best hobby ever enjoy

 

[weatherboxes]

weatherboxes they digital/electronic ballast {thats not starting ? } U gotta leave them a few mins before firing them up again / try this+hope it helps .. ur on the right road to sucsess my friend , yea the intake extract can get baffling / seems u might have it susses now tho . i agree with freezer boy a 600 would b nice in ur room or the 2x400 MH+HPS mixed lighting / or the 1K blowing air straight through the hood and out of the growroom . the best hobby ever enjoy

true that im thoroughly enjoying this hobby. but yeah the ballast wouldnt fire up my metal haloid. its kind of alarming because there is no on and off switch on my hood or digital ballast you just plug it in and unplug it to turn it off. it isnt plugged into the power surge because for whatever reason I prefer it plugged directly into the wall. i hope thats the problem im going to the hydro store after class today so ill talk to the guys there about it and pick up my temp/humidity monitor and timer.

 

[FreezerBoy]

They make special timers for just this purpose. After power returns, it delays delivery to the lamp for 10-15-20 minutes so things can cool down.

 

[ThaMagnificent]

Do you have any odor control?

 

[weatherboxes]

Do you have any odor control?

No I don't at the moment. I am growing for medicinal use however and have my recommendation from the doctor so I'm 100% legit. Probably wont end up having any odor control for two plants.

I bought my therm/humidity monitor and its about 78.9F-80.4F(it fluctuates) with 30% humidity. Its about 90 degrees today where I am at on the coast.
The MH is on an 18/6 timer right now and I will start my grow journal probably tomorrow. With the MH off the box stays at about 72F-75F. I have two 4 inch passive intakes now.