How much airflow you need for CO2

reddan1981 said:

ok my mate, have you got c02 meter, if so would you be able to control an experiment properly ? (An effective control )

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jijiandfarmgang said:

I've been saying this for a while, but for some reason instead of intelligent debate people many people just say I'm flat out wrong.

Everyone keeps spouting "I heard you need airflow 1-5 times per minute to keep CO2 levels high." Or "you need plenty of air exchange for CO2", or "plants need fresh air" etc.

In my experience this just isn't true. Let me get one thing straight. I'm talking about "NEED" not "IDEAL".

In general (In the typical indoor growing world) its more important to focus on environmental temps, and humidity. If you need to exchange air in your room say every 2 times a minute to keep temps down, then you should do it. But if your intaking very cold air all the time and using heaters, because you think the plants need fresh air, your doing yourself a disservice.

A couple years ago (I can't remember the numbers) I tested a 3k indoor grow room with a CO2 monitor. It was in a home that was drafty (3/4 inch gap underneath door, no vapor barrier or tyvek, probably not much insulation). This room was sealed with no CO2 gen. At all times, this room had a decent amount higher CO2 content than outdoors.

Recently wanting to prove a point I wanted to do an more thorough job and datalog an outbuilding grow. I'm running into a few issues datalogging but here are the inital results.

4k grow room built in a barn. Drywall, and fiberglass insulation. No caulking, No vapour barrier (this may or may not be important). The room is sealed in winter. Entering the room once per day for tending, watering. High of above 2000 ppm while in the room (this number is unimportant as I was near the meter, while it was initializing). Now 24 hours later I entered the room and checked the meter 441 ppm CO2. When I checked memory for the minimum recorded CO2 it was 423 ppm CO2.


- Jiji

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reddan1981 said:

you can't accurately monitor data I think because your room isn't airtight. I don't think you'll prove your point with this room currently.

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reddan1981 said:

ok I agree it doesn't take alot of exchanges to replenish and full controls and accurate data are unnecessary to your situation so just keep an eye on your temp and exchange air when outside your preferred temps, c02 data is unnecessary because your room isn't sealed

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bravedave said:

Not sure about that, but yes I know what it takes to replace my rooms air. "My" rooms co2 availability level will peak at the time of replacement while the rooms temp will be at its lowest as the air bringing in the co2 is cold. Directly after replacement my room almost immediately returns to its normal, pretty constant temps and starts using this new co2-filled air. What we want to know is how long before Co2 levels drop to a level below what the plants "need" and we need to replenish with new air again. The less I need to replenish with this cold air the better. So, we are mainly talking co2 availability, not use.

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reddan1981 said:

supping on my coffee also lol ill stop blocking your conversation brother.

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bravedave said:

Very nice!! ?. You give the starting ppm but suggest it was not noteworthy. Seems a reading directly after air replacement would be. I suppose you could assume the rate of decline, even. Although it might be interesting to check other intervals. Oh and...What is the light?

Regardless, this is great stuff! @dluck I HAVE a room without a co2 tank that relies on pulling outside air in to replenish co2. The air can be very cold, so I really would like to avoid doing it often. This tells me that my 9 replenishments I am doing can be reduced further.

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bravedave said:

My room may not be sealed but it is tight. There is virtually no air exchange unless the exhaust is pulling air through the intake or the door is opened. So, The co2 data DOES provide some necessary info even to my room.

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jijiandfarmgang said:

Well it wasn't noteworthy under the circumstances. Me using it and breathing next to it trashes the data. It should be put somewhere and left alone and just log data for a week.

The light was 4000 watts



The same as my outdoor room. Otherwise it wouldn't retain enough heat. No heaters, down into -30s and only a dehumidifier warms at lights out period.

- Jiji

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jijiandfarmgang said:

Well thats kind of the point. The data is as accurate as the meter. Most people don't have a room airtight. All I was trying to prove is that visiting the grow once per day keeps acceptable CO2 levels, or perhaps even higher for quite a period of time instead of ventilating. I wish my datalogging setup was working to prove that.

- Jiji

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dluck said:

I guess why im confused is most ppl use bottled CO2 in indoor grow rooms or if they don't then just a sufficient air exchange for temp purposes .

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dluck said:

My air intake is pulled from inside house into the grow area..I don't draw air directly from outside...I'm guessing most my co2 comes from all the ppl and dogs that's in my house that exhale co2.

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bravedave said:

Understood noteworthyness of your number, just saying that with my situation a reading at the full replenishment point would be good to know. Of course, I guess a reading outside the room where the intake is, should give you that easy enough.

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reddan1981 said:

again I might have misinterpreted but unless supplementing with C02 how would levels rise?

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jijiandfarmgang said:

People use CO2 in rooms for IDEAL or at least theoretical IDEAL CO2 levels. I'm not saying this way is better.

My point is, if you don't use CO2, your probably better off exchanging air for temp/humidity purposes not because you just think you need to exchange air all the time.



This is good. Personally I think C02 injection is overrated. People post a lot of anecdotal evidence, but as far as statistical evidence for the avg indoor grower it just isn't there.

Now comparing outdoor CO2 levels 380ish to 1500ppm in a lab, or controlled environment, such as studies at Ole Miss, I have no doubt that C02 is going to trump outdoor levels by a statistically significant amount.

I'm thinking the reason why is that most people have small grows inside their home where CO2 levels are naturally high. And in many cases higher than they should be for a home (sick building syndrome).

So compiling all my thoughts and OPINIONS, CO2 injection as far as yield is concerned, if you can intake air in your home isn't going to change plant growth much.

Now if your grow is in an outbuilding C02 injection is much more feasible and should significantly increase plant growth, HOWEVER it is not necessary for decent plant growth.

Clear as mud?

- Jiji

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