Power of exhaust/intake fans

[SirGrowAlot]

I know that your fan needs to be able to pull out in cfm the area of your space in 5minutes. Is it bad if say you have a 200cfm exhaust fan but only 70cubic feet of space??
Also, i know when you have an exhaust fan you need an intake fan to bring new air in. What is the relation in power to the two? Does the intake fan need to be stronger?

Thank You in advance for your input

 

[rj-jizzle]

U should be fine with the 200cfm. I personally think the more air out is better. I dont have a intake for my veg room it jus has a exhaust fan but there is intake vents. I did put a intake n exhaust in my flower room they r boththe same size.

 

[Malcolm]

A intake would definately increase Co2 and thus growth and can be the same size. You should be able to use the one fan for both intake/exhaust, hope this helps...
Malcolm...

 

[SirGrowAlot]

Awesome....
I had heard all kinds of different things.
THx guys

 

[SmokzAlot]

Food for your brain...

You speak of CFM and having a 70CFM cabinet or area. One must keep in mind that is a free running, no heat load rating. Once you start complicating a system those numbers can change a lot. Duct is resistance as well as filters and light hoods. There are some great in depth articles here on 420mag that cover the details and formulas if one desires.

To address the intake vs exhaust question. Intake fans are often not used in small applications as there is adequate negative pressure to accomplish the job. Meaning it will suck in what it needs as long as the hole is big enough. Once you start covering distance the idea of an intake fan comes to be a viable option. What you are doing here is maintaining air movement in the room, and more even distribution of CO2 from the incoming air. Mileage varies depending on room and fan configurations. For example, when I speak of distance it is relative to the source not the room of air. In other words how far is the outside from the area you are treating? That may require a booster on the intake.

Make any sense for you?

 

[SirGrowAlot]

A intake would definately increase Co2 and thus growth and can be the same size. You should be able to use the one fan for both intake/exhaust, hope this helps...
Malcolm...

Do you have any pics of a setup of how you can use one fan for intake and exhaust?? Or can you explain it to me?
Thank You

 

[SirGrowAlot]

Food for your brain...

You speak of CFM and having a 70CFM cabinet or area. One must keep in mind that is a free running, no heat load rating. Once you start complicating a system those numbers can change a lot. Duct is resistance as well as filters and light hoods. There are some great in depth articles here on 420mag that cover the details and formulas if one desires.

To address the intake vs exhaust question. Intake fans are often not used in small applications as there is adequate negative pressure to accomplish the job. Meaning it will suck in what it needs as long as the hole is big enough. Once you start covering distance the idea of an intake fan comes to be a viable option. What you are doing here is maintaining air movement in the room, and more even distribution of CO2 from the incoming air. Mileage varies depending on room and fan configurations. For example, when I speak of distance it is relative to the source not the room of air. In other words how far is the outside from the area you are treating? That may require a booster on the intake.

Make any sense for you?

So when you talk about the CFM on the fan, what you are saying is that with running it thru ducting, filter, and hood that it wont actually even clear out 200CFM by then bcuz the filter, hood and ducting would decrease the power of it? If it does decrease it, about how much? By half?

 

[SmokzAlot]

Do you have any pics of a setup of how you can use one fan for intake and exhaust?? Or can you explain it to me?
Thank You

I'll jab at this if everyone don't mind. I will do my best to make it simple for you.

Think of your grow space and a box full of air and sealed tight. You want to take air out to remove heat and possibly odor. Have you ever sucked a plastic bottled drink dry and sucked that last bit out? Notice the bottle begins to collapse on itself. That is negative pressure. Vacuum to be precise. Notice as well as this point you can draw no more from that bottle. Not till you let some air in anyway. Think of water and air the same. If you push water into a closed container it fills to capacity then stops taking on any more. Unless you put a hole in the opposite end. Now it can flow through the space. This is what you are after with an exhaust fan. Allow a large enough hole to relieve the vacuum but maintain negative pressure so it captures and removes the intended target. At this point you have achieved flow through ventilation intake and exhaust with one fan. How much air you need to move is another topic.

Air can't come out if it can't get in, nor can you put in what you can't take out. When was the last time you blew into a pop bottle. It takes so much then no more. A good place to start is if you have a 6" fan give it a 6" intake, your mileage can vary.

Let's K.I.S.S. this thing...

option 1
hole air in -> grow space -> hole out exhaust fan

option 2
hole air in -> (grow space -> filter) -> hole out exhaust fan

option 3
hole air in -> (booster fan -> grow space -> filter) -> hole out exhaust fan

option 4
hole air in -> (grow space -> filter -> lights) -> hole out exhaust fan

option 5
hole air in -> (booster fan -> grow space -> filter -> lights) -> hole out exhaust fan

Anything beyond this is a whole other animal. Usually requiring separate systems for intake and exhaust, and another for lights.