Using CO2 To Fight Heat

I’m worried about my room getting too hot for my plants to grow. What’s the hottest you would let your room get before using air conditioning? Also, would using CO2 help me not have to run the a/c? I’ve read a lot of positive reviews regarding using CO2 and that it will help your plants grow when the room exceeds the temperature plants need to photosynthesize?

What are you using for light? There’s a couple of studies suggesting ideal canopy temps for leds is higher than hps due to lower leaf surface temps.

I’m using LED. I also SCROG half, if not most of my plants. I’m worried because I know it could get over 100 degrees and I’ve heard good things about CO2. I’m not opposed to running straight a/c to keep temps cool, but I’m looking for a cheaper option.


Didn’t @TDubWilly run CO2 at one time?


I use co2 because having two or three oxygen making plants in a inclosed area. I don’t open my doors but once a day so no air exchange, I have to add co2. My two leds only run 85* during summer, so not sure if it helps with temps

Even if you run ac in a sealed room you will still need to supplement co2. The plants will deplete ambient co2, then there won’t be any remaining for the plants to continue processing.

@Myfriendis410 he did, but I don’t think results justified cost and inconvenience. So he may have ditched it.


So tell me what you think of running a/c during the hottest part of the day (noon-7 pm), then also using CO2 throughout the day? If I do something similar to this, how hot do you think the room could get before I should begin to worry?

With high levels of co2 and high humidity, you can run up to 95F, per Jorge Cervantes. But we’re talking using a co2 tank and regulator or generator for 1000+ ppm of co2, not hanging an exhale co2 bag and calling it good.


I was going to buy a 20 pound tank with an autopilot desktop CO2 monitor. How long do you think a 20 pound tank could last?

Am I looking to keep my grow room humid? I was aiming to try to stay between 80 and 90 degrees while running CO2 and a/c. I was going to try to use a carbon filter as an exhaust fan to push some heat out and a dehumidifier to try and keep humidity low.

For high temps and co2 enhancement, high humidity (70-80 RH) is the accepted practice, makes for faster growth conditions. Check out the VPD charts.

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What is your opinion on humidifiers?

It’s nearly impossible for any of us to know how long a 20 lb co2 tank would last. Depends on how big the room is, how many plants, how healthy are the plants, what are your light density numbers, what ppm are you trying to maintain, how much air does your exhaust move, and how often is it running. Even if you crunched all those numbers, they’re not going to stay the same throughout an entire grow.

I would say unless you’re talking about an extremely small space, a 20 lb tank won’t last long enough.


I put my LED drivers outside my tents and have vented my tents to the attic. I was running 84F in the tents before and it felt hot when I walked into the room. Now the tents run in the low 70s during the day and I get concerned about it getting too low overnight (low 60s.) Doing those 2 things made a big difference.


Also, would terpenes be reduced by high temperature? We were having this conversation a few days ago. Frankly, I would give up potency for aroma.


The money spent in co2 to grow in 100° temps would exceed what it cost to run an air conditioner.

Co2 is not used to combat heat. It is an addition to an already perfect grow room. You’ll spend more money growing with this mentality. Cheaper for you to run an air conditioner instead.

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Not long. Depends on the size of the room. I have an 12’x8’ room that is about 85% sealed, so I have some leakage, but my 20 pound tank would last about a week

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