# ventilation pros needed



## loolagigi (Feb 19, 2010)

ok, closet size is 5x 4.5x 8'.  i have a 465 cfm cage fan.

i am going to be running 2- 400 watt cooltubes. i will pull air from the room, through the cool tubes, and out. i will also have a passive a/c inlet somewhere in the room that will add cool air when the house a/c kicks on. 
heres the q...i think it would be good to have another passive intake. i was going to use the vents at home depot for cosmetics and such. what would be a good size?
will any of this even work, lol?  thanks, Loola


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## loolagigi (Feb 20, 2010)

dont be shy


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## The Hemp Goddess (Feb 20, 2010)

I think it sounds like it will work.  You will need to do something so that light cannot enter (or escape) from your passive inlets.  

Are you running 4" or 6" ducting?  Ducting that is 4" is 12.56 sq inches, 6" is 28.26 sq inches.  Your passive intakes, IMO, should be larger (in sq inches) than your exhaust.


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## loolagigi (Feb 20, 2010)

The Hemp Goddess said:
			
		

> I think it sounds like it will work. You will need to do something so that light cannot enter (or escape) from your passive inlets.
> 
> Are you running 4" or 6" ducting? Ducting that is 4" is 12.56 sq inches, 6" is 28.26 sq inches. Your passive intakes, IMO, should be larger (in sq inches) than your exhaust.


cool. im using 4" ducting. thanks hg


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## DonJones (Feb 20, 2010)

Since you are probably going to have to restrict your air flow on your passive intakes, shoot for twice the square inches of the outlet.

That is easy to do using the wall vents from HD or Lowes although they do Nothing to stop light transfer.  Depending upon what you have available for room outside of the grow room, there are several ways to baffle them, but that is dependent on a lot of factors.  

One of the simplest is to build a box twice as tall as the vent and twice as deep.  Paint it flat black inside. Put the outlet to the grow room at the bottom of the back of the box and the inlet from your fresh air source at the top with a baffle in the middle that hangs down a little over half way to stop direct light flow to the grow room.  The more baffles you put in, the less light gets through but also the less air that it will flow too.

Another way is to use 6" ducting from HD or Lowes, adjust 2 elbows to 90 degrees each, pain them flat black inside, assemble them so that they make a 90 degree turn followed by another 90 degree turn; mount one end to the wall and screen the other end.  If space is a concern they can be adjusted to that the second elbow points up, down, or sideways parallel to the wall rather than sticking out into the outer room/area.

If I have confused you, PM me and I'll try to clarify what I mean.

Great smoking.


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## PieRsquare (Feb 20, 2010)

loolagigi said:
			
		

> ok, closet size is 5x 4.5x 8'. i have a 465 cfm cage fan.


 
I found this info from another weed site:


*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.


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## loolagigi (Feb 20, 2010)

thanks guys, awesome info.


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## PieRsquare (Feb 20, 2010)

loolagigi said:
			
		

> thanks guys, awesome info.


 
You're very welcome! I didn't even see: "2. Then divide by Pi (3.14)" in regards to the pun.  until I re-read it!


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## matt612346 (Feb 25, 2010)

for a closet with 180cubic feet, 465 is soooo over-kill lol


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## zem (Feb 26, 2010)

a higher rated fan than needed is great to have since you can get a fan controller and run it on lower rate this makes the fan very silent. the more ducting and curves the less efficient the venting, it's always good to make the ducts bigger to allow easy airflow


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## legalize_freedom (Feb 26, 2010)

I like overkill in the ventilation dept.!


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