Temps too high? Add solid volume to your box!

I don't know why this didn't occur to me until I observed it, because it's pretty common sense. And since most people in this forum (CFL) are growing in PCs or small cabs, I figured it may help someone.

I had been struggling with keeping temps down in my veg box.. Sometimes it was in the 90s sometimes low 80s, and the exterior environment was about the same. I have two fans for each box (veg/flower), one intake and one exhaust. Both are the same fan/cfm/size.But my flower box, with higher wattage lights was cooler. I thought it was just due to cab materials and how I mounted the fans.

Here's what I noticed: when my flower box had two plants, the temps with all lights on stayed at about 84+/-3. Removed one plant to harvest (and it's "pedestal") and the temps now average 92 +/-3 or so. Nothing else changed.

In my veg box, temps were like 94-95 at times, had to vent the damn thing all day long to give the plants a break. Added some boxes to put two party cups on and the temps now STAY at 82-84. I did notice that changing from reflective mylar to black/white panda film also dropped temps a few degrees.

So what I assume is happening is that the extra solid volume (plant, boxes, etc) are displacing air, which means less air your fans have to move to replace what was in there, which means less air there is to heat (or at least, air stays in the box for less time, not getting as hot).

I swear, it's so simple it's dumb. But my temps dropped almost 8 degrees from nothing more than putting extra crap in my box.

TL;DR: Put extra things in your grow box/cab to displace air and your temps should drop some.

extra shit in your grow box will lower temps.??? doesent make sense to me.?

So basically you're saying by having more things inside of an enclosed area you are displacing (moving) air out of the area. So if there's less volume of air within the area for a fan to exhaust, there's less heat because the fan can exhaust the lesser amounts of air faster?

Makes sense I guess, but you're still limited to your room temperature without A/C or ice no matter how much your fan circulates the air in the box because unless your intake is A/C your still going to be stuck with your room temperature air.

It did for me. I think my problem was, the exhaust wasn't able to move enough air to get the hot air out before it got really hot. When you add solid mass inside the grow box, the air that used to occupy that space has to go somewhere. And once you close her up, your empty volume (the space that is occupied by air) has decreased. So now there is less air for my fans to move, so the air cycles through the box quicker, and since that air doesn't "sit" in the box as long, it doesn't get as hot.

I could have the same results by adding an extra exhaust fan to move more air. But that's extra work (and money) when I can just throw some empty baseball card boxes in there and drop the temps

Hupomone said:

So basically you're saying by having more things inside of an enclosed area you are displacing (moving) air out of the area. So if there's less volume of air within the area for a fan to exhaust, there's less heat because the fan can exhaust the lesser amounts of air faster?

Makes sense I guess, but you're still limited to your room temperature without A/C or ice no matter how much your fan circulates the air in the box because unless your intake is A/C your still going to be stuck with your room temperature air.

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Yes! And yes that's true. if you already have an optimized system that is sitting at room temp, then this isn't going to do much for you. But if you are like me, with 90+ degree temps in a 74 degree ambient room, it can help dramatically

Tokeroo said:

It did for me. I think my problem was, the exhaust wasn't able to move enough air to get the hot air out before it got really hot. When you add solid mass inside the grow box, the air that used to occupy that space has to go somewhere. And once you close her up, your empty volume (the space that is occupied by air) has decreased. So now there is less air for my fans to move, so the air cycles through the box quicker, and since that air doesn't "sit" in the box as long, it doesn't get as hot.

I could have the same results by adding an extra exhaust fan to move more air. But that's extra work (and money) when I can just throw some empty baseball card boxes in there and drop the temps

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Yeah. It's a good DIY thing, but I don't think anything will compare to just having nothing but your plants in there. You want the extra volume of air in most cases that's why we get bigger exhaust fan so we can circulate all of our air faster. More fresh air for the plants is better rather than a small amount of air. Even more important considering a micro grow in a PC box in my opinion.

I'm not sure if you considered that or not but that's what I think. I would only use this method as a temporary solution to keeping temps down while I got a better exhaust.

Boy thats some hethan talk I tell ya right there, you better stop smokin' that devils lettuce boy, drag you straight to hell I swear! Mylar is more heat reflective than panada film, that is why it is useful material as a disposable emergency blanket. It does a good job at keeping whatever it is wrapped around insulated with heat. That is probably what helped the most.

Hupomone said:

Yeah. It's a good DIY thing, but I don't think anything will compare to just having nothing but your plants in there. You want the extra volume of air in most cases that's why we get bigger exhaust fan so we can circulate all of our air faster. More fresh air for the plants is better rather than a small amount of air. Even more important considering a micro grow in a PC box in my opinion.

I'm not sure if you considered that or not but that's what I think. I would only use this method as a temporary solution to keeping temps down while I got a better exhaust.

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Very true. The problem is, this is in a closet w/o much room to work with. So, I may be stuck with sub optimal conditions (and sub-optimal harvests) until we can afford to add on to the house. Though, I may be able to add another fan, or rework the light trap to let more air through.

i agree with hupo.. one of my buddies has a rubbermaid grow going on..temps got to high 80's- low 90's.. he added a secondary exhaust fan and Boom... temps sit steady at 75-79*...i plan on adding some extra fans so i can run a few more cfl's..my cab sits at roughly 77* and i only have 117 watts running....might move the cab to the basement cuz its cooler down there..or maybe an AC.. who knows..

check ebay bro youll find fans for dirt cheeap

Yeah. You can get a 6 inch in-line fan that pulls 400+ CFM for less than a hundred bucks. If you can afford to grow you can afford to buy the proper exhaust fan for that area. Figure it as just part of the growing cost (it really is).

EDIT: For smaller grows you can buy 200mm PC fans that move like 150 CFM for around $20 or even 120mm that move about 80 CFM for $10-$15. They are good because in most micro grow you aren't as concerned with static pressure, just moving the air.

Hupomone said:

Yeah. You can get a 6 inch in-line fan that pulls 400+ CFM for less than a hundred bucks. If you can afford to grow you can afford to buy the proper exhaust fan for that area. Figure it as just part of the growing cost (it really is).

EDIT: For smaller grows you can buy 200mm PC fans that move like 150 CFM for around $20 or even 120mm that move about 80 CFM for $10-$15.

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amen to that brotha

Yeah I have 120mm fans now. This one actually: http://www.newegg.com/Product/Product.aspx?Item=N82E16835168006

I just don't have any more, and really don't want to hook any more up if I can help it - but I may have to. I used a 230w AT power supply, so I got the juice. Fuck all that cell phone charger bullshit

the only way this would work is if you added a large chunk of ice to your grow room. adding mass that is cooler than the surroundings will cause that object to absorb the heat, warming it up, and cooling everything off. eventually things will equalize and your heat problem will continue.