Passive intake feedback please

[Vhghost]

Hello all, been a long time but I'm setting up for something and would love a bit of feedback.
Subject is - passive intake and is it large enough, will this work?
Room is 7.5'x12'x9'tall and will house 3 600w hps sea of green or 2 1000hps for vert.. Still undecided.
I'm looking at 420cfm(6inch)fan with a scrubber venting into the attic(of the garage).
As for the passive vent opening I plan on using a cheap filter on the outside wall and a carbon odor reducing filter on the inside wall(filters are 25x20x1 standard house furnace filter)
My question is, will I have enough air flow through the wall if I build out the inside with a box and remove the non load baring stud and reenforce the 2x4 above and to hold insulation and direct air flow? Also staggering the air filters so I don't have light leaks.. Should this work?
I appreciate all the help.
Outside

Inside

 

[Phaeton]

I am a firm believer in positive pressure bud rooms to keep out pests and pollen. Odor control in an open room wooden building is questionable so putting a larger fan on the intake and using a passive exhaust with the carbon filters should not make more smell.

The bud room here uses one CFM per watt. 5600 watts takes two 24" (2700 CFM) fans to push air in and an eight inch hole lets some of it back out, maybe 800 CFM get used. Temperature control is easier in a pressurized room, the exhaust port gives direct feedback that can be felt with a hand. Intake adjustments are more difficult to gauge and a seesaw effect often ensues.

 

[Old Toker]

How did you choose a 420cfm(6inch) fan for the size of your grow area?

 

[Vhghost]

Thanks Phaeton, I'll take that into consideration.

Old Toker- 768 cubic feet in the room, so I figured if I run the fan 420cfm I should be able to exhaust the hot air out of the room in 2 mins no problem(also I had it sitting around). if I ran a variable fan speed controller with a smart thermostat, meaning it will run the fan the entire time lights are on keeping the Temps right where I need them(odor control). Night time Temps I'll have a heater until summer hits, then ac.

 

[Illuminate]

Its very good to have +pressure, but in my case it would mean i wouldnt be able to use all my space, or if i had stanky weed everyone would know. You can filter an intake and have -pressure, keeping your smell in and limiting pest intake through filtration and sealing where you can. How does a passive extraction work with a filter?

 

[Vhghost]

At the other end of the room 12feet away will be my fan sucking air through the scrubber at the top of the room and out.

 

[Illuminate]

Is it only passive in the sense that its less cfm than the intake? If you had a room within a room + pressure in the inner room is fine if the outer room is filtered and still - pressure.

 

[Old Toker]

Old Toker- 768 cubic feet in the room, so I figured if I run the fan 420cfm I should be able to exhaust the hot air out of the room in 2 mins no problem(also I had it sitting around). if I ran a variable fan speed controller with a smart thermostat, meaning it will run the fan the entire time lights are on keeping the Temps right where I need them(odor control). Night time Temps I'll have a heater until summer hits, then ac.

JMPO.....but 1800 - 2000w of HPS is going to be too hot for that room without more airflow. How are you cooling your air?

 

[Phaeton]

In winter the intake air is zero to -30 F and is blended to +40 F. In the summertime the 8" exhaust is opened up to five square feet and airflow is closer to 4,000 CFM than 800.

Ambient temperatures make a heck of a difference. The garden lights will heat the house down to -20, that is a lot of heat to shed in the summertime.
Running the fans at full bore with the door open (5,000 CFM flow through) will keep the room six degrees over ambient. When summer temps hit the 80's it is all over and the lights are switched to nights.

No amps to spare for running AC, using 80 amps of a 100 amp service already, box is warm. I had kids and no garden when the house was built, did not need gobs of power.

 

[Illuminate]

You guys are sure blessed for indoors up there if you have back up gennys or constant power.

 

[Vhghost]

This room will have cold fresh air drawn into the room through the filter. I have pretty cold Temps so the air entering the room will be quick to cool the lights. If I have to I'll run an ac.