Help with growroom setup - ventilation specifics

High everyone,

I'm new to the rollitup forums, and self sufficiency in general so please be patient if my questions seem basic.

So I have a small setup in a basement, with 1 home built box measuring 1.4 x 1.4 meters with a 600w HPS. 4 x C99 feminized in SCRoG, currently 7 days into 12/12 after 2 months vegging from seed, in NFT. The screen is the full size of the box and is very nearly full. There must be close to 150 tops/shoots poking through the screen, plants looking very healthy and growing QUICK! I have a powerful fan on both intake and outlet (carbon filter too) and the box is completely sealed (no leaks). I am confident the air exchange in this box is way above what it needs to be.

I also have a 1.2 x 2.4 meter secret jardin tent set up with 2 x 600w HPS in it. Again, with both intake and outlet fans more than capable of adequate air circulation, and carbon filter. There is nothing in here currently but soon will have 6 x clone from my best of the C99's, again in NFT with SCRoG screen same size as the tent.

However, due to the urban location of this setup I have decided to seal up the natural air vents from the basement to the outside world, to prevent any smell leaks when working with the doors to the box open. The basement itself is about 3.5 m square. Now I am coming into flower time, I am worried about the available CO2 for my ladies. Although my plants are performing well now, the flower period is only just starting, and very soon my canopy area will triple in size (when tent is up and running).

So, my question is this. Should I install an air intake fan to suck in fresh air from the outside world, to provide optimum CO2 levels, or will the setup perform well as it is? If I fit an intake fan, do I also have to fit an exhaust fan? If I fitted an intake and no exhaust, would be pushed up through my floorboards etc as a means of escape (as I would assume)? Or will leaving the basement door open for an hour each morning be sufficient for decent air exchange?

One option I could use is to fit the intake and exhaust fans to the outside world and turn them off before I open tent/box, leaving them off for an hour or so after box closed up again so smell isn't such an issue before turning them back on. (However, remembering to do this every time I want to check PH could be an issue ). I guess I could even run another fan with carbon filter on it as the exhaust fan, with the carbon filter before the, fan so the fan sucks the air through the carbon filter rather than blowing it through it like it does on my outlets on the grow areas? (a fairly expensive fix)

Another tactic could be to have the two areas on opposite photoperiods time wise. So, dark in the tent, lights on in box, and vice versa. Would the photosynthesis of one offset the respiration of the other, or would the effect be negligible?

The other option I could consider is CO2 enrichment, but I know little to nothing about this. My local shop sells fungus based CO2 enrichment cubes/gas burners for enrichment, but both are fairly expensive and from what I have read Co2 enrichment only makes much of a difference if your grow is dialled in. As I am a novice, I guess I will be a good ways off being dialled in!

What would you do?

Any help and input greatly appreciated.

One Love.

There is a higher concentration of CO2 in your home than there is outside. Not so sure about in the basement, but in living quarters.

Air exchange is good, but plants don't use CO2 that fast, so whatever general pointers you find are usually baseless in my experience.(baseless as far as CO2 is concerned, not heat or humidity)

It won't make the biggest deal whatever you do.

- Jiji

Thanks for the reply. Although as a rule there may be more CO2 within a house than outside, the basement at the moment is pretty much sealed off - so my concern was that the flowering plants would use most of the available CO2 within the sealed environment, to the point where it would start to impede growth. Is this not the case?

chronicboomz said:

Thanks for the reply. Although as a rule there may be more CO2 within a house than outside, the basement at the moment is pretty much sealed off - so my concern was that the flowering plants would use most of the available CO2 within the sealed environment, to the point where it would start to impede growth. Is this not the case?

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I don't know for sure. I've tested quite a few scenarios with a CO2 meter, but not one that similar to your scenario.

I'm almost positive you wouldn't know the difference.....but I could be wrong.

The only scenario I could get the CO2 levels noticeably lower than outside, was with an outdoor small grow room with a fair amount of foliage, that was sealed and not accessed for 24 hours. The sealed part is important. Because when it was just a normally built "sealed" room, going in once a day, CO2 was fairly stable. Once I went around and sealed and caulked every seam, then it used up CO2 more than I'd like.

Either way you can ventilate from inside or outside, my main point is you don't need to exchange much air at all.

- Jiji

jijiandfarmgang said:

I don't know for sure. I've tested quite a few scenarios with a CO2 meter, but not one that similar to your scenario.

I'm almost positive you wouldn't know the difference.....but I could be wrong.

The only scenario I could get the CO2 levels noticeably lower than outside, was with an outdoor small grow room with a fair amount of foliage, that was sealed and not accessed for 24 hours. The sealed part is important. Because when it was just a normally built "sealed" room, going in once a day, CO2 was fairly stable. Once I went around and sealed and caulked every seam, then it used up CO2 more than I'd like.

Either way you can ventilate from inside or outside, my main point is you don't need to exchange much air at all.

- Jiji

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Lets put it this way, how long do you think you could stay down there before you would die of oxygen deprivation, assuming the plants weren't there to help make O2? If it was as sealed as you think it would be just as possible for a person to use up the O2 as it would be possible for your ladies to use up the CO2. I've never heard of a person using up enough O2 in any part of a home to get light headed. That is an analog for the point where the plants would suffer from CO2 deficiency.

nomofatum said:

Lets put it this way, how long do you think you could stay down there before you would die of oxygen deprivation, assuming the plants weren't there to help make O2? If it was as sealed as you think it would be just as possible for a person to use up the O2 as it would be possible for your ladies to use up the CO2. I've never heard of a person using up enough O2 in any part of a home to get light headed. That is an analog for the point where the plants would suffer from CO2 deficiency.

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I think your trying to agree with me? But it happens all the time SBS sick building syndrome.

- Jiji

Edit: IMHO CO2 is like PHing soil, its talked about a whole lot in the forums. But unless something is drastically out of whack it matters very little.

jijiandfarmgang said:

I think your trying to agree with me? But it happens all the time SBS sick building syndrome.

- Jiji

Edit: IMHO CO2 is like PHing soil, its talked about a whole lot in the forums. But unless something is drastically out of whack it matters very little.

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Really, from lack of O2? I've heard plenty from leaks of various types, but never heard of someone depleting the O2 by breathing, I would love to see an example.

Not so much from lack of O2 but CO2 buildup.

http://www.epa.gov/iaq/base/pdfs/base_3c2o2.pdf

- Jiji