CFM exhaust confusion, what?

[baet]

closet is 2.5' wide x 6.25' long x 6.75' high, so my CFM is 35 if i want to circulate air out every 3 minutes because my CF is ~105.
i read on a website to add 10-15% to your CFM for every uncooled light and 20% if your using a carbon filter, ill have one 600 watt HPS uncooled and a carbon filter attached to my exhaust fan.

15% of 35 is 5.25, so im at 40.25 CFM.

20% of 35 is 7, so im now at 47.25 CFM if i want to circulate air out every 3 minutes.

the smallest size exhaust i found is 60CFM which is what i would use. that seems small when comparing to other peoples exhaust fans, and when reading the sticky in this forum "calculating the size of an air conditioner" it says to add like 250CFM for every 600 watt HID to your already existing CFM...?



im lost, either a 60CFM is ideal from using that websites approach or a 35CFM + 250CFM(600w HID) is ideal from using that sticky's approach.


what size CFM exhaust fan do i really need for a 2.5 x 6.25 x 6.75 room with one 600 watt HPS uncooled and a carbon filter?

 

[enojadoperro]

60 cfm won't cut it, thats for sure.
You'll want to use the second idea and try 285cfm or more.
A 6" inline fan and a speed control would be the best option as it gives you the ability to go up to 400+cfm if needed.
It's always better to get a stronger fan then you think you need then to buy one too weak and need to go buy a stronger one later.

 

[Guest]

2.5' wide x 6.25' long x 6.75' high comes out to 105.5. 105 two or three times a minute is 210 - 315 cfm. Then you can do those percentages or what have you.

lengthxwidthxhigh = 2.5x6.25x6.75=105.5 . where is that 35 come from you have?

using uncooled, assuming ambient temps are manageable, lean toward the higher side with 315 cfm imo with good airflow in the space ifself

 

[baet]

eno-thank you, yup, gonna have to spend a little more money hah. i feel you, rather do it right than have to go back and spend more money.

MSG-woops, i was taking 105 and dividing by 3 for some reason, rather than multiplying by 3... fuck. im sorry, im gonna go with 315cfm fersure. thank you very much for clearing this up.

 

[baet]

im looking at the ecoplus 6" 440cfm, is there anything wrong with having quite a bit more cfm, i need 210-315 but i install 440cfm? most good brands go from like ~170 and jump up to 400ish cfm..

 

[619Sativa]

You could always use a fan speed control. There like $25.

 

[baet]

619-perfect, thanks. sounds like a plan, ecoplus 6"

 

[baet]

MSG-correct me but i thought the room had to be vented out every three minutes, fresh air that is, so if my cf was 105 wouldnt i want a fan that can do a third of that every minute, like 40cfm so every three minutes i would have vented out 105 CF? i know im wrong, could u just explain to me what i have wrong...

 

[Jnugg]

Dude,do not pay attention to e-sites that sell fans and tell you you need to get a fan that replenishes the air in the grow space 1-3x every 5 minutes.

What you want is an inline centrifugal that will replenish the air in the grow space 3-5x every minute....trust me on this one.

You've been told to get a 6" 400+cfm inline centrifugal...the person that posted that is correct.

You should take a look at the links in my sig like,HOW DO I DESIGN A FAN POWERED COOLING SYSTEM FOR MY GROW BOX,VENTILATION 101.

For just air-cooling a light in an air-cooled hood you would want a ratio of 0.3-0.5cfm per watt,so an inline centrifugal that is rated 120-200cfm just to air-cool a light in an air-cooled hood.

As far as ventilation for the cab,an inline fan that can remove and replenish the total volume of air in the cab 3-5x per minute,so if your grow spaces total volume in cubic feet is 105.5 cubic feet for ventilation purposes ypou would want an inline centrifugal that is rated 316cfm.

So again I would suggest a 6" inline centrifugal that is rated 392cfm-440cfm....I would look into air-cooling that 600w HPS though if I were you.

 

[baet]

jnugg-thanks man, yeah im getting the 6" ecoplus 440cfm. pretty stoked. thanks for clearing it all up. someone gave me a link the other day for figuring out my cfm in a grow room, and it must be wrong. shitty

 

[ItsAllOver]

You say once every 3 minutes, I say 3-5 times a minute. Big difference. I think this rule of thumb has gotten messed up somewhere.

Sweet call on the ecoplus! You're going to be moving along in no time.

 

[baet]

yeah rule of thumb i got came from here, thats why i was confused.

http://www.bghydro.com/bgh/static/articles/0606_vent.asp
^^^
"Step 2 – CFM Required
The fan should be able to adequately exchange the air in a grow room once every three minutes. Therefore, 512 cubic feet/3 minutes = 171 cfm. This will be the absolute minimum cfm for exchanging the air in a grow room."

 

[Dr. Conjuror]

Dude,do not pay attention to e-sites that sell fans and tell you you need to get a fan that replenishes the air in the grow space 1-3x every 5 minutes.

What you want is an inline centrifugal that will replenish the air in the grow space 3-5x every minute....trust me on this one.

You've been told to get a 6" 400+cfm inline centrifugal...the person that posted that is correct.

You should take a look at the links in my sig like,HOW DO I DESIGN A FAN POWERED COOLING SYSTEM FOR MY GROW BOX,VENTILATION 101.

For just air-cooling a light in an air-cooled hood you would want a ratio of 0.3-0.5cfm per watt,so an inline centrifugal that is rated 120-200cfm just to air-cool a light in an air-cooled hood.

As far as ventilation for the cab,an inline fan that can remove and replenish the total volume of air in the cab 3-5x per minute,so if your grow spaces total volume in cubic feet is 105.5 cubic feet for ventilation purposes ypou would want an inline centrifugal that is rated 316cfm.

So again I would suggest a 6" inline centrifugal that is rated 392cfm-440cfm....I would look into air-cooling that 600w HPS though if I were you.

Jnugg - Ok now I am a bit confused. I have been trying to do a good bit of reading here for the design of my cab (which will have a separate fan for the cool tubes). You mention an exchange rate of three to five times a minute (just for the cab's/room's volume,) but Red mentions in Ventilation 101 that plants are happy with one exchange per minute and this is what I have been spec'ing on. I was curious as to why three to five exchanges per minute would be needed. Is it to provide enough CO2 or what?

Thanks,
Dr. Conjuror

 

[Guest]

Dr Con, plants need the fresh airflow of the space being exhanged once a minute, if ambient temps make cooling not a problem.

The space itself needs to be exhausted more than that when managing heat thrown from a HID lamp.

Red was talking imo about plants requiring fresh air as opposed to the cfm required to manage heat in confined spaces.

 

[Jnugg]

Jnugg - Ok now I am a bit confused. I have been trying to do a good bit of reading here for the design of my cab (which will have a separate fan for the cool tubes). You mention an exchange rate of three to five times a minute (just for the cab's/room's volume,) but Red mentions in Ventilation 101 that plants are happy with one exchange per minute and this is what I have been spec'ing on.

Thanks,
Dr. Conjuror

Dr Con, plants need the fresh airflow of the space being exhanged once a minute, if ambient temps make cooling not a problem.
The space itself needs to be exhausted more than that when managing heat thrown from a HID lamp.

^ Couldn't have said it better myself lol.

Most people (not all) that I see growing on this site or setting up an area are planning on using one fan to either ventilate the growspace and air-cool the lights via air-cooled hood or ventilate the area and try to keep the area cool when not using a non air-cooled hood...this would require a fan that can remove and replenish the total volume of air within said growspace 3-5x per minute.

Now if using one fan to properly air-cool a light (outside air>ducting>air-cooled hood>ducting>outside air) and another fan dedicated to ventilation is where things change.

0.3-0.5cfm per watt for air-cooling a light.

Get fan that can replenish the air in the grow space once every 3-5 minutes (although I still would prefer something along the lines of 2-3x per minute just to be on the safe side and be sure there is a good level of Co2 (I don't supplement with tanks/regulators or generators,just good old fresh air supply).


When you get into the realm of supplying Co2 via a tank and regulator or a Co2 generator is when you step into the worl of Sealed Rooms.You can still use air-cooled lights in a sealed room,but you better make sure that it is set up properly and that no grow room air gets into the hoods,otherwise you are wasting the Co2.In a sealed room no ventilation fans,just an air conditioner too keep growroom temps around 85f.

 

[!!!]

If you're still looking for something in the 200-235 range, Panasonic has a 240 CFM in their Whisper* (WhisperFit, WhisperValue, WhisperLine etc) line of fans. They're known for being dead quiet. I ordered a 240 CFM, I think it runs at 1.4 sones (noise measurement).

I have a 400W (cooltube) and my room is about 70 ft^3. I do have another 400W I'd like to use for lighting (800w total) but for that 240 CFM might not be enough. I'll burn that bridge when I get to it.

Keep in mind that a bigger fan also means a bigger carbon scrubber. A small scrubber may not be effective as the air will not have enough contact time with the carbon.

 

[BLUNToPOTomuss]

Jnugg said it IMO! I use .3-.4 CFM per watt for cooloing ONLY! then go with 3-5x exchange a min. on top of that and I've had no problems keeping my 400 hps and cab cool. in fact I have a hard time getting the cab up to ambient.

good luck

 

[baet]

yeah im starting to wonder if my single 440cfm exhaust hooked up to a carbon filter will cool my 90cf grow cab with a uncooled 600 watt hps...

during the day when the lights on we would be able to open up the closet and let sum hot air out though, pretty much whenever. its ina friends room

 

[baet]

i just talked to a guy that is doing a cab exactly like mine will be setup pretty much, 440cfm vortex, 600 watt uncooled hood, and carbon scrubber, with relatively same size cf and hes keeping temp during light on 70-74!

 

[Dr. Conjuror]

Ok MSG, Jnugg, and BLUNToPOTomuss we all seem to be on the same page. I have been calculating 300cfm per 1000 watts of lighting in its own cooling system (and I think that is to maintain the 10F* difference in ambient and exhaust, which Red has said is usually a little cooler than need be). But I am still unclear as to what is really needed for respiration for our flora. I just do not see them breathing that much air in that amount of time. Let's say we had one cubic meter of grow space. I know in twenty seconds (three exchanges per minute), there is no way I could even exchange one cubic meter of air in my longs, much less process it. I do not think that however many plants I was able to realistically stuff in that cubic meter, they would be able exchange that amount of air in twenty seconds.

Please pardon all ramblings, musings, and misconceptions on my part.

Dr. Conjuror