Trouble Calculating CFM/Carbon needed

Ok so here it is. I'm gearing up to grow in a closet that 68"tall 42" wide and 28" deep. I ran the numbers using a post from grasscity forum that i found. but im getting numbers that seem to be way to high. so my question is in 2 parts:
1. Do these equations accurately predict the amount of CFM and carbon filter size needed?
2. Did i just mess up the math or do i really need 463 CFM & 22 lbs of carbon for a closet this size using a 600 watt HPS, 200 watt T5 & 150 watts of misc equipment?

CFM Req:
3.5'Wx2.3'Dx5.6'T = 45.08'ft3 x 5 (#of exchanges) = 225.4CFM
950 Watts (equipment total)/4(AEC)=237.5 AEC CFM
225.4CFM+237.5AEC CFM =462.95CFM Total

Carbon Req:
462.9CFMx60minutes=27,774CFH
27774CFHx0.36g/foot=9998.64g
9998.64g/448 g per lbs=22.32lbs of Carbon

Any feedback would be cool. Thanks!

Math is fun, but it is only as good as the formula given

The formula is not scientific it is something someone pulled out of their ass

Just match a carbon filter with rated fan. I would go with a 6 inch medium size filter a the largest.

Thanks for the reply jiji. But i dont think any old 6 inch is going to do it. I was hoping to get some input on what would be enough if this equation is bunk. I mean its a rather small room for a 600w all things considered and as always budget is a concern. I dont have enough to get a nice 900 cfm 8" inline as i would like to so i could put a decent controller on it and be able to adjust even if i upgrade to a 1000w at some point. Any ideas where i could look for more information? Ive been all over the site and have been unable to find something that will help me predict how much ill need exactly.

jijiandfarmgang said:

Math is fun, but it is only as good as the formula given

The formula is not scientific it is something someone pulled out of their ass

Just match a carbon filter with rated fan. I would go with a 6 inch medium size filter a the largest.

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so if I'm doing 4000 watts in a 10' x 10' tent, I need like 1500 or more cfm? is that correct? jesus!

Did I perhaps post this in the wrong thread unknowingly?

Dude, refer to my previous post.

A 6 inch centrifugal fan and matched quality carbon filter such as phresh or phat would be overkill for even just what a 1000 watt bulb could grow.

This is from experience not some 13 year old kid spreading bs.

If you want to go way overkill get the 6 incher and fan, with a variac (not a fan speed controller) then you can dial it down.

Jiji i appreciate the input and you say your not just some kid spreading BS, and im not calling you out, but Id think if you actually knew what you were talking about you could offer me some evidence other than "I said so". For all i know you are a 13 year old kid with no experience growing anything. Now if you were a high ranked member i might take your word for it but since your still at the bottom, can offer no evidence of your claims and have now tried to tell me that any 6" is overkill for a 1000w (which i know isn't true from my own experience), please either offer up some proof or stop trying to make claims you cant backup.

jijiandfarmgang said:

Dude, refer to my previous post.

A 6 inch centrifugal fan and matched quality carbon filter such as phresh or phat would be overkill for even just what a 1000 watt bulb could grow.

This is from experience not some 13 year old kid spreading bs.

If you want to go way overkill get the 6 incher and fan, with a variac (not a fan speed controller) then you can dial it down.

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What do you want me to prove, or how?

Smell is subjective. Different strains smell more than others. Air flow, enviroment and especially humidity play major roles. Different carbon is more effective than others etc. Formulas don't work so well.

I know you think that using one 600 watt or 1000 is bigtime, but it isn't.

I am paranoid about smell and have invested more money in carbon filters, ozone generators and ona gel than you can imagine.

The closest thing I can think to use as evidence is that No one else that I have even seen uses near that amount of carbon for a closet grow. Its kind of what the other poster was hinting at.

Ditch the notion that the formula has any credibility. Think about it, think what a carbon filter does, then think why would wattage of misc. equipment in growroom be a part of the equation?

jijiandfarmgang said:

What do you want me to prove, or how?

Smell is subjective. Different strains smell more than others. Air flow, enviroment and especially humidity play major roles. Different carbon is more effective than others etc. Formulas don't work so well.

I know you think that using one 600 watt or 1000 is bigtime, but it isn't.

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Who ever said anything about a 600w being "big time"? now your just making shit up. stop hating and offer any kind of proof or stop posting nonsense.

jijiandfarmgang said:

I am paranoid about smell and have invested more money in carbon filters, ozone generators and ona gel than you can imagine.

The closest thing I can think to use as evidence is that No one else that I have even seen uses near that amount of carbon for a closet grow. Its kind of what the other poster was hinting at.

Ditch the notion that the formula has any credibility. Think about it, think what a carbon filter does, then think why would wattage of misc. equipment in growroom be a part of the equation?

Click to expand...

obviously you have no idea what your talking about. Watt's are directly correlated to heat, the more heat the more CFM needed to maintain proper temps. Please offer any kind of tangible evidence at all for your claims or stop posting. And by evidence i mean some real time numbers. Maybe your cubic feet vs. your air exhaust rate (accounting for the length of your ducting etc.) posted with your avg temp and humidity. you know the kinds of things that might actually back up the things you say.

Cannabidude said:

obviously you have no idea what your talking about. Watt's are directly correlated to heat, the more heat the more CFM need to maintain proper temps. Please offer any kind of tangible evidence at all for your claims or stop posting your ignorance.

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First of all, I know I'm coming off as a cocky bastard, but I'm seriously not trying to be one

I get what your saying, yeah cfm extraction heat, makes sense, etc........BUT there's a desired ratio for cfm to carbon. Figuring weight of carbon alone for plants or light wattage or etc doesn't make much sense as there are so many variables.

Most premade carbon filters have a recommended cfm for effective scrubbing. Pulling to much cfm through a small filter degrades its filtering quality.

I agree. But as i'm on a limited budget my point in this post is to get baseline so i can get something the 1st time that will work so i don't have to buy more equipment. I can adjust for quit e a few variables myself but i'm not used to this problem as all of my previous grows have been much larger so overkill was king and we slowed down our fans to remain quiet. In my current setup i don't care so much about noise but have limited funds. I never tried to actually calculate to get as close to the correct air exchange as possible. All im really looking for is to spend as little as possible but still be sure i can ventilate my room correctly, keeping the air exchange rate in line while still cooling the room down to the appropriate temp. (also i edited my post above after i re read how it sounded )

I wouldn't take those equations at face value, but one good point made is the number of air exchanges per minute. The other part taking into account what equipment you are using could prove to be wildly inaccurate.

The part that I believe is giving you the most trouble is where they add the air exchange and equipment values together. Assuming the equipment value is right (it's not), you would just pick the highest flow rate of 237.5. 5 exchanges per minute is on the higher end of what is recommended to provide plants with a healthy amount of fresh air. If you need to have more flow to combat the heat, that's fine, but the plants will not make use of the additional CO2.

As far as the carbon goes, I'd say the most important aspect of the filter is not the amount of carbon, but the thickness of the wall and the velocity of the air moving through the carbon. Carbon filters are designed with a specific surface area to be paired with a specific fan resulting in a velocity through the carbon that effectively scrubs the air.

However, I would recommend against making a filter. Other than those who have made multiple filters, I would expect that many of those who have made their own single filter saved little to no money, spent too much time, or experienced poor performance. Been there done that.

So, my advice would be to search through grow journals for someone who has used a similarly sized space, similar lighting, and similar temperature conditions (season, part of building, intake locations). See what fans they have successfully used, and price out that fan and a matched filter.

IMHO, the fan and filter are the components to splurge on. You can always dial an over sized fan back, but you will find yourself with the most frustrating situation if you decide you would like to have more airflow. Small spaces are a bitch.

I know these are probably not the answers you wanted, or you already knew, but small grows especially are far too diverse to have a simple ventilation equation. You could learn some heat transfer and try to come up with a rough prediction, but even that is not worth your time.

I think this is good advice. although i did check out grow rooms of similar size before posting and as you would expect it seems like everyone has a different exchange rate. I think ill just say fuck it all and get the 500cfm fan and keep it turned down. May be overkill but at least i wont be screwed if a 200cfm wont cut it.

GrowinSmoke said:

The part that I believe is giving you the most trouble is where they add the air exchange and equipment values together. Assuming the equipment value is right (it's not), you would just pick the highest flow rate of 237.5. 5 exchanges per minute is on the higher end of what is recommended to provide plants with a healthy amount of fresh air. If you need to have more flow to combat the heat, that's fine, but the plants will not make use of the additional CO2.

As far as the carbon goes, I'd say the most important aspect of the filter is not the amount of carbon, but the thickness of the wall and the velocity of the air moving through the carbon. Carbon filters are designed with a specific surface area to be paired with a specific fan resulting in a velocity through the carbon that effectively scrubs the air.

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yeah your better exceeding your need, instead of falling short and cooking your girls