Ventillation help please?

I'm making a box to hold 3-4 plants and planning on making it about 5.5ft tall, 4ft wide, and 1.5-2ft deep..
(about 40cu ft)
I'm planning on using a centrifugal fan (panasonic whisperline version, they make 120, 240, 480cfm)
I'm thinking 240cfm (maybe even 120cfm) would be enough for this application..any thoughts from someone who's done it?

I'm planning on having it pull air through a carbon filter -> cool tube -> out of the box.

Any thoughts on what would be best for tihs? If I make another box and have more ventillation than I need can I put a splitter and have it pull air from both boxes?

Any help/thoughts/ideas/anything is appreciated greatly. I'm trying to not waste money I don't have.

Thanks,
CreQ

BTW I'm cooling a 400w light..
I'm also wondering does a 480cfm running on a controller at half speed = the same as a 240cfm one running at full speed? As far as suction power and stuff..
I'm wondering if I should just buy bigger than I need and tune it down..
I was just thinking that maybe a 240cfm one running at full speed might have more 'pulling' power, and be able to pull through the carbon filter better than a 480cfm one running at half speed..
Is this true or is my understanding of how tihs works way off?

....make sure the new air is coming in from the bottom of the room, and as far away from the filter as possible. This brings in colder air, and allows it to cross all of the room to get to the filter. Good luck.

Thanks, and yeah I'm planning on that and sucking air from the top of the cab..
I don't know if it'd be better to have a straight air in->tube->air out inline cool tube with some duct boosters blowing air straight in&out of the box without mixing with the inside air (so I don't have to put a filter/no smell) and then a centrifugal fan sucking air thru a carbon filter & out of the box..
or if it'd be better to put the carbon filter/cool tube all on the same duct with the centrifugal fan only..

I'm trying to put this together quick and was wondering what other people did on their HID cabs for ventillation...
Anyone mind giving me the info on what their setup uses?

You can check out my thread. It woks great. Stable temps and no smell until you open the door. You can always slow a fan down but you cant speed it up.

https://www.rollitup.org/grow-room-design-setup/279041-homemade-grow-cabinet.html

Skeeter

Thanks, and yeah I was just looking at your thread like an hour ago =P
I guess I'll get the 480cfm model then for the extra $ and maybe I can exhaust a second box with it if I end up making it..

This brings me to a final question:
Higher CFM movers seem to have higher diameter ducting (6-8" as opposed to 4") and this is going to be passing through a 4" diameter cool tube no matter what..

Is the higher CFM one designed for 8" ducts better even though it's going to end up pulling through a 4" duct for at least part of it? Or will adapting it to a 4" duct size seriously reduce the operational capabilities of the 8" ducted fans?

driving a 8" through a 4" will make a lot of noise and that presents a security threat!

If you blow the air you don't need the carbon filter on the tube light you still need it for the box if you can't vent above the roof.

Ventilation is about controlling the quality of air, CO2, heat and humidity in the grow room. To
achieve a high quality of air in your grow room, you need to ensure that there's a sufficient amount
of air exchange. The amount of air exchange required will vary according to the temperature
outside. But as a general rule, maximum winter ventilation rates rarely exceed 12-20 air changes
per hour; however, maximum summer air exchange rates can go up to 60 air changes per hour.

4" fans are more than enough for 40 cf.

Example
1. A grow room of 3m x 2m = 6m2
2. Required air flow rate = 6 x 125 = 750m3/hr

check out more here

http://www.aquaculture-hydroponics.co.uk/admin/web-inf/uploads/documents/ventil-bound.pdf

Peace

Hope this helps.
Here’s how you can calculate the amount of ventilation you need. If for instance you wanted to keep you grow room temperature from getting any more than 5° warmer than the intake air temperature, and you were using 400 watts of power, you’d make the calculation below in blue. The chart is based on the following formula. It is a well-established heat transfer formula.


(3.2 × 400) ÷ 5 = 256



The Home Ventilating Institute recommends one square foot of open air inlet per 300 CFM of ventilation fan capacity.

If you were going to use 256 CFM, you’d want 256/300 square feet of intake area, which is 122.88 square inches.

Here are some options for the intake area for a 256 CFM ventilation fan:

1 hole - 12.5 inches in diameter.
2 holes – 8.84 inches in diameter.
3 holes – 7.22 inches in diameter.
4 holes – 6.25 inches in diameter.
5 holes – 5.59 inches in diameter.
6 holes – 5.11 inches in diameter.


Here is how to calculate the hole sizes:

1. Take the total area in square inches needed, in this case 122.88 square inches, and divide by the number of holes you want.
2. Then divide by Pi (3.14).
3. Take the square root of that value.
4. Then multiply by 2.

The answer is the diameter that each hole would need to be to make up the total area needed for intake.

A large number of small holes will create more backpressure than one large hole of equivalent area. This would be negligible unless you’re using a huge number of holes or you’re using ducting to supply the air to each intake hole. If you’re just cutting them in a wall you should be fine using 8 or less holes without having to take into account the extra backpressure.

Nice chart. Based on how my cabinet runs it seems to be right on.

I have still some questions though..
I can get the 240cfm whisperline model for 140 shipped..that seems cheaper than a TD150, and it's not going to use its full 240CFM after it has the filter right? That's going to create quite a bit of SP..
Can you filter AFTER the fan? Blow through a filter? Or is this not good?
Could I put the filter on the other side of the reflector opposite to the air intake side, and then put a bigger duct (like 12" duct) over that air tight somehow and have it suck air thru?
I can't figure this out..
I'm trying to figure out now, how to filter this..
I have a 6"port air cool reflector glass enclosed, but it's not air tight, it has cracks and quite a few. If I filter before it goes in the light this is going to create leakage and smell exiting the box.
I need to figure out how to filter either after the blower if that's possible, or if it's possible make an inline filter?
anyone?? =xx i'm starting to go nuts trying to figure this out and doing the calcs.. but there's no way to account for static pressure so I'm gonna get an overkill fan no matter what and just tune it down as needed..I'll prob get the 440cfm model..and it's not much more, better to have more than less, and I'm planning on making a veg box maybe I can vent both with it.

I still can't figure out how to filter it though, I bet they make very expensive inline filters, but I might would get one if I have to..