Tutorial Ventilation 101

[moonshoes]

Hi, this may be a stupid question but if my cab is 29.66 cu ft what size fan should I get?

I saw one I want that moves 190 cfm but it seems overkill for my space. Do you guys think the advertised cfm is even accurate?

I need smell control but am not sure how to mount the duct to the wall of the cabinet and what speed of fan to get. Also, how to cut an opening for exhaust? Does it have to be a circular cut?

 

[HushemFlupskluk]

Hey Moonshoes,

The overkill can be dimmed with a dimmer. This would save the cost of a new fan. I got dimmers for 2,50 Euro each.

For veg I would try to get slow airflowspeeds. But during flower you want more flow to prevent rot from manifesting in your flowers.

Maybe you can drill the exhaust opening out. But I would get a circular saw to do it. Best is to have a nice clean cut

Grts

 

[dante76]

new to this thread and need help with configuring what hardware i need. My setup is a 4.5x4.5x6.5 tent with a 1000w MH and a 400cpm fan for cooling the hood.

From what i read in the this form, i should get a blower too, correct? Redirecting the air from the hood to circulate in the tent is not a good idea. Am i on the right track here?

Considering the cubic feet in the tent, should i go with a 265 cfm blower or a 465/495 blower?

Will either the 465/495 blower give too much air that could dry out the plants?

Right now conditions are really cool between 60 - 65 degrees/50% RH indoors. Which blower should i consider at this temp of air?

thanks

 

[HushemFlupskluk]

Hey Dante,

The heat from the hood/bulb can be used to redirect it to cirtculate in the room. Here the heat can be usefull for maintaining optimal temperatures. But when the temps outside the room go up i bet you want to redirect the heat of the hood outside the room. Here you would serve the same goal but you apply the other technique.

Using aircoolers and heaters will enable you to have an unchanged blowers setup inside the room, but the powerconsupmtion will increase alot. Using thermocontrolled exhaust/intake-fans will consume less power.

Until you have this type of climatecontroll you will be moving the blower around when the 'room out' temperatures fluctuate over time.

But a stable room out temperature would save you the investments and work. This situation enables you to have a static blower setup also.

Blowers are dimmable. And yes the plant could dry out especially when they are very small. If they reach out in the room they can handle more speedy airflow without suffering alot.

 

[ekomsi]

Currently My intake consists of an (active intake) it's 2 4in holes bringing in fresh air from under a deck with 2 inline 4in vauline fans on each 4in pvc intake.

My exhaust is the can filter 100 with a 8in High Output Canfan.

Im replacing the exhaust with a 12inx39in Phresh Filter (1700CFM) and a 12in Vortex fan (1140Cfm)

Im wondering if I need to add more 4in holes for my intake??? And How many I keep getting confused b/c Red says that your intake could be 2x bigger then your exhaust but Freezer Boy says there needs to be Negative pressure which I figure the outake needs to be bigger then the intake.

Either way I want my room to have a proper sized Intake hole to match my exhaust. Please Help!

 

[driska]

Welcome!
in my box I have 3x1.5x2m 800mh3 fan that pulls air so that when I close the vacuum pulls the tent together. I wander if it can be a problem in flowering?(in vege i didnt have problem).
I have the perfect humidity, for air intake, I have 200mh3 that pull direct air from the outside

 

[Piel]

Hi, Thanks for a lot of info, I read every thread upto page 8 so I think I have the circulation pretty much down etc.

My question is probably dumb but please don´t laugh: I´ll be installing a fan for pulling in air and I want to blow it out threw a scrubber (carbon filter) but I was thinking of putting that before the exhaust fan: scrubber->fan->out but you guys seem to be doing it the other way around?

Or have I completely missunderstood the whole thing.

Please be kind when replying 95% of my grows have been outdoors.

 

[StoopheadFred]

You can either pull air through the scrubber (like what you're doing) or push air through it. When you push air through a filter it skips the prefilter step and will cause premature filter wear, plus you have to mount the filter outside of your box / room. When you pull through a filter larger particles get caught in the prefilter before being filtered more finely through the actual carbon layer.

What type of fan are you using? From what I've heard pulling through a fan can be problematic because some fans aren't sealed properly, allowing unfiltered air to seep in and be filtered out of the room.

Now I've got a question! I know intake holes are supposed to be double the size of the exhaust hole... I just want to make sure that this will still allow me to achieve negative pressure inside the cab?

 

[Snook]

Finding intake wind speed

Finding intake wind speed

I've seen, on sail boats and around air craft this little 3 prong, cup looking, wind speed gathering whirly bird jammies. Dont know ship about them (or what they are called) except they measure wind speed.. could this, or something like it, be used to measure intake air speed? Not saying all this previous info here is not excellent, it is. I'm curious about how much more input/exhaust is required to maintain a tent/room when it is filled to the brimm with budding plants vs veg, when they are 14inches tall. I'd think that if intake speed is 100 (whatever) at veg, it might be necessary to run 150 during mid to late bloom.. dono.. ??
wasted ATM

 

[Piel]

Thanks for the feedback! I´m looking at something around this line:

http://www.head-nature.com/04111

It seems to have what I need.

 

[gdbud]

Now I've got a question! I know intake holes are supposed to be double the size of the exhaust hole... I just want to make sure that this will still allow me to achieve negative pressure inside the cab?

In side my cabinet I placed two register grills that I'm able to open and close to damper the air flow down if needed.



I inserted these in to a box with light traps and a filter on the back side to filter the air before it enters the cabinet. Since the grills are at the bottom where the pots sit it does not interfere with the plants at all.

 

[guest 77721]

It's been a while since I visited my old thread. Looks like it's purring away on it's own quite nicely.

Hey Snook, that 3 cup anerometer measures windspeed. You can get hand held models that look like a little fan. If you know the airspeed just multiply it by the duct area to get the flow rate. I have the full calculation on the first couple of pages.

I've seen, on sail boats and around air craft this little 3 prong, cup looking, wind speed gathering whirly bird jammies. Dont know ship about them (or what they are called) except they measure wind speed.. could this, or something like it, be used to measure intake air speed? Not saying all this previous info here is not excellent, it is. I'm curious about how much more input/exhaust is required to maintain a tent/room when it is filled to the brimm with budding plants vs veg, when they are 14inches tall. I'd think that if intake speed is 100 (whatever) at veg, it might be necessary to run 150 during mid to late bloom.. dono.. ??
wasted ATM

 

[moresntoil]

how much flow can be forced through 4"?

how much flow can be forced through 4"?

Hi everyone,

So I have a question in reguards to ventilation, lets say someone is using a 4" duct to exhaust outside, and currently vented through a set of 6" cooltubes with a 6" exhaust(vortex type).

If the 6" blower was changed out to a 10" blower but still went through the 6"duct and then down to the 4" duct would the airflow increase a great deal?

basically, if using a 4" vent what is the max diameter blower that could be used to get the greatest exhaust rate before the 4" duct will limit the flow rate?
Would going from 10" to 8" to 6" help rather than from 10" to 6"

Thanks Moresntiol

 

[painroad]

Any suggestions for a 10x10 tent with 1k hps cooled hood? I have 2 1ks but will only be running the 1 light for now. Temps are gonna be going up here soon and i don't have AC. Also where can i mount fans with out making the walls humm? Can i put fans on the ground? The wife is bitching about the hummm... is there some kind of rubber garmiitt i can use?

pain~

 

[lbezphil2005]

Any suggestions for a 10x10 tent with 1k hps cooled hood? I have 2 1ks but will only be running the 1 light for now. Temps are gonna be going up here soon and i don't have AC. Also where can i mount fans with out making the walls humm? Can i put fans on the ground? The wife is bitching about the hummm... is there some kind of rubber garmiitt i can use?

pain~

you hang the fans with bungee cords, bro. There are quite a few threads talking about that. Use rubber and bungee cords.

 

[moresntoil]

Hi everyone,

So I have a question in reguards to ventilation, lets say someone is using a 4" duct to exhaust outside, and currently vented through a set of 6" cooltubes with a 6" exhaust(vortex type).

If the 6" blower was changed out to a 10" blower but still went through the 6"duct and then down to the 4" duct would the airflow increase a great deal?

basically, if using a 4" vent what is the max diameter blower that could be used to get the greatest exhaust rate before the 4" duct will limit the flow rate?
Would going from 10" to 8" to 6" help rather than from 10" to 6"

Thanks Moresntiol

please everyone not at once, lol
think i figured it out thanks

 

[StoopheadFred]

So I have a question in reguards to ventilation, lets say someone is using a 4" duct to exhaust outside, and currently vented through a set of 6" cooltubes with a 6" exhaust(vortex type).

If the 6" blower was changed out to a 10" blower but still went through the 6"duct and then down to the 4" duct would the airflow increase a great deal?

basically, if using a 4" vent what is the max diameter blower that could be used to get the greatest exhaust rate before the 4" duct will limit the flow rate?
Would going from 10" to 8" to 6" help rather than from 10" to 6"

Thanks

Moresntiol

The fan's exhaust hole size is 10" not 4" for a reason... ya know? By making the diameter smaller you're going to be increasing the resistance to air flow. Any reason in particular you can't match that 10" or get closer to it than 4"?

There will be more airflow. But it will probably be hard on the fan because the airflow resistance will increase with the increasing amount of air trying to force its way through that small hole. You may get a lot more rushing noise as well.

And 10 - 8 - 6 will be better because it's a more gradual progress for the air to flow through. If the air has to go from a 10" hole directly to a 6" hole it will encounter more resistance.

 

[moresntoil]

Yes there is a reason the 4" duct must be used, otherwise it would be sized closer to the exhaust fan size....would rather not get into why a 4" is being used...

but the noise is a good point, thanks bro

 

[guest 77721]

Hi moresntoil,

the discussion you and fred are having regarding duct size reductions is a common misconception with fans. Most people think a fan with specified flow rating will produce the rated flow under all conditions and that is false.

A fan is a pressure producing device and the flow is a result of the sum of the restrictions in the ducts and chambers that the air flows through. Total Pressure = Static Pressure + Velocity Pressure. Flow = sqrt(Vp)A. Less static pressure losses means more flow.

For instance if we have a 6" fan and a 4" fan from the same manufacturer and design and they both produce 1 inch of pressure. Because Flow = sqrt(pressure)Area, the 6" fan generates more flow than the 4". If you reduce a 6" to a 4" though ducting, the flow will be the same as a 4" fan with a 4" duct because both fans produce the same pressure, only the area has changed.

Bottom line is don't make any unnecessary reductions in your ducting.

 

[MrStonerMan]

I have a question on ducting and was wondering if anybody could help me out. I have 3 different cabs in my space right now 2 veg/clone and 1 flower cab. Currently my flower cab is the only one venting out the window. My flower cab seems to work well enough to exchange the air for the whole room but I am wanting to connect all 3 cabs to exhaust out the window. Here is my question: If I connect all 3 fans to the same exhaust vent will I alter their performance at all? The reason I ask is because I have 2 6 inch booster fans venting my veg cabs and A 6 inch valuline fan venting my flower cab. The valuline fan puts out about double the CFMs as the booster fans. Should I just vent them each to a separate exhaust?