2 720 cfm fans somehow not enough to maintain temps? Any advice?

Well I'm running into some temp problems and I really can't quite tell why. I have a 6x10 room that's about 7 ft tall that I built within a 10x12 room and it's pretty much completely insulated, some patches on the wall aren't completely insulated but the roof and bottoms of the walls are. I'm running two 1000 watt bulbs in there now and here's how it's set up.

ducting out of the box <- 720 CFM inline fan blowing air out < 1000 watt air cooled hood < ducting < 1000 watt air cooled hood < open ducting hole

So that one fan is blowing the hot air from the lights out as well as sucking some of the hot air out through the opening in the end of the hood.

My other 720 cfm inline fan is the exhaust for the entire box and it's blowing the air out of a window. I also have a tiny booster fan blowing air in from the bottom of my house since it's probably the coolest air I'll have access to even in the summer.

My neighbor has a grow room that's about 10x12 and he's running 3200 watts with no temperature problems at all. He has no exhaust for the box at all and is only running one single fan for all 4 of his lights. And not only that, he's somehow using less electricity than I am.


The only conclusion that I can possibly come to is that I'm royally screwing something up and something isn't being as efficient as it should be. What are common problems that would result in my temps being this high with all the fans that I have? One 720 fan should be plenty to keep the two lights cool, yet they aren't as cool to the touch as I want them to be. They don't completely burn my hand but they aren't completely cool to the touch either. Is it perhaps that my room isn't insulated properly? Maybe there's some hot air seeping in from some cracks that I don't know about and my room isn't insulated enough?

Should I be finding ways to cool the room my grow room is in as opposed to my grow room? The exhaust for the box itself is blowing outside of my house but the exhaust from the vented hoods is blowing into the room my grow room is in.. do you think that's raising my temps a little? I'm doing my best to avoid using an AC because the way I see it that's electricity I can use for more lumens and I don't want to raise my electric bill anymore if I don't have to. My temps get to 85 and I want to be able to maintained 75-80 degrees. Will this be impossible if the ambient temps of the room my grow room is in aren't cooled? Should I focus on cooling the room the grow room is located in instead of the grow room itself? I've done so much reading and research and thought I did everything right but this is just stumping me. Any and all help would be greatly appreciated because I know there's something wrong, I just don't know what.

Edit: Oh and by the way, I have 3 oscilating fans in the room for air circulation.

Your lights are heating up the ambient temp of the main room.
Can you vent the lights out the window as well ?

What you have is the lights hitting a surface and heating it up. Much like the sun does to the pavement. That in turn transfers heat to the room air.

First it's hard to compare rooms. He could have his temp gauge in the shade or lower to the floor.

I run a sealed basement room with 3 1000's ducted in an isolated loop from outside the room, through the lights, and then outside the house and I still have to run an AC to keep temps in check.

I would personally change it so your exhaust from the lights goes outside and not into the room. You could also think about adding C02. You would increase your growth and the plants will tolerate higher temps.

Im Trying to understand what you have going on , you have plenty of cfm to due the job,

1. you need to duct correctly: from what Im reading you have not done soo.

2. you need enough fresh air entering the room from a outside sorce; 720 cfm needs 144 sq inches of opening so the fan can be supplied with fresh air, Any opening or ducting to bring the fresh air in if not at least 12'' x 12'' or 12'' round will hinder your air exchange rate dramaticly.

3. when exhausting all air is pulled ,not pushed . pulling = neg pressure / pushing = static pressure (this is called supplying air what you want is to exhaust air.

4 FYI remember pressure and tempeture go hand and hand , anotherwords when pressure is increased tempeture is increased (nature of the beast) this is another reason why exhaust is pulled not pushed.

jrainman said:

Im Trying to understand what you have going on , you have plenty of cfm to due the job,

1. you need to duct correctly: from what Im reading you have not done soo.

2. you need enough fresh air entering the room from a outside sorce; 720 cfm needs 144 sq inches of opening so the fan can be supplied with fresh air, Any opening or ducting to bring the fresh air in if not at least 12'' x 12'' or 12'' round will hinder your air exchange rate dramaticly.

3. when exhausting all air is pulled ,not pushed . pulling = neg pressure / pushing = static pressure (this is called supplying air what you want is to exhaust air.

4 FYI remember pressure and tempeture go hand and hand , anotherwords when pressure is increased tempeture is increased (nature of the beast) this is another reason why exhaust is pulled not pushed.

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I know right? I'm trying to understand it myself as well. I'm gonna take some photos tomorrow and post everything for you guys to critique even more. But until I take these photos (gotta wait for the lights to come on) what do you feel would be ducting errors? I was thinking that my ducting was incorrect but I tied everything down and what bends I do have are 45 degrees instead of 90 degrees so as to not kill the efficiency of the fan.

I really think that points 2-4 really apply to my room as opposed to point 1. I think my ducting is connected fine and once I put photos up I believe they will also reflect that. However, what I do believe I'm messing up on are points 2-4. I don't have a 144 sq inch hole for passive intake, I currently have two 4 inch passive intake holes because I thought those would be enough for my one 720 cfm fan for the room.. is that incorrect? I think it may also be worth pointing out that I didn't have any temp problems until I installed the fan and my intake holes.. so either the problem is with my fan or intake holes and since it's not the fan it must be the intake holes. Do I need to make them larger? What sizes would you recommend for each hole or would you just recommend one? Are there any other ways that I can work to reduce the pressure in my room? I sincerely think that this is the problem because although it's been getting a bit hotter lately, it really hasn't been by that much. My temps were a constant 72-78 until I installed my intake holes so I'm guessing I did something wrong with that? You gave me the exact criticism I need, if I could ask you for a bit more help I would greatly appreciate it!

Yodazherb said:

Your lights are heating up the ambient temp of the main room.
Can you vent the lights out the window as well ?

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I thought that this may also be a problem because my lights are venting into the main room and the window is just wide open with nothing drawing the hot air out. That being considered I can see how all the hot air would fester and build up until it raises my temps. I could vent it out of the room like the box's exhaust, however the problem is that I'd need 10-15 ft of ducting so wouldn't that be just as counterproductive? Or do you think it would help with my temp problems despite making the fan work harder? Thanks a bunch for your input!

Opm said:

What you have is the lights hitting a surface and heating it up. Much like the sun does to the pavement. That in turn transfers heat to the room air.

First it's hard to compare rooms. He could have his temp gauge in the shade or lower to the floor.

I run a sealed basement room with 3 1000's ducted in an isolated loop from outside the room, through the lights, and then outside the house and I still have to run an AC to keep temps in check.

I would personally change it so your exhaust from the lights goes outside and not into the room. You could also think about adding C02. You would increase your growth and the plants will tolerate higher temps.

Click to expand...

You know, I actually do have my temp gauge on the floor. I had it in the soil of my plants but took it off because I was afraid of getting the gauge all wet and ruined.. perhaps I should hang it at canopy level instead? lol! I really want to vent the light out of the room and it's looking like I'm gonna go the extra 10-15 ft route. If I could cut a hole in my wall I could just vent it straight out with only using 2-3 ft of ducting but I don't think my landlord would be cool with that. He's very supportive of my growing but not cutting a hole in the wall.. if I were to do that though how hard would it be to fix? If I can guarantee I can fix it I'm sure he'll let me destroy the whole room so long as I reimbursed him for it. It's looking like I'm gonna have to do this because if I'm fighting 80-85 temps now summer is going to be killer. I can understand needing an AC for summer time, but any other time is just no excuse.

And what are the average start up and continuing costs of running CO2? I've been really interested in doing so but I've heard it's way expensive, but for my climate it's sounding necessary (especially in summer!) I may be running a 2k set up, but I didn't spend more than $1000 on the whole set up and I've always heard CO2 can be almost as much as my whole set up in some cases!

Thank you all so much for your replies, this is exactly why I posted this on here! I think it's extremely interesting that all 3 replies offered me completely different advice, all of which completely relate to my particular situation. I would love to get a bit more info from you guys if you all wouldn't mind. I hate to ask questions because everyone does it so often without reading anything, but rest assured I've done boatloads of research and have implemented it all which is why I'm so stumped that my temps are this high! I used the search function (and google) for rollitup, grasscity, and ICMag as well as reference my Rosenthal grow bible but no matter where I search the best info I got pertaining to my problem was these three replies. If you guys would please give me a bit more of your time to help me fix this problem I would be forever grateful. And if I may ask another question, do you believe that upgrading to the XXXL hoods will help my temp situation or do you think it's just a waste of money I should be spending on an air conditioner?

Thanks guys!

Main key is exhausting OUT.
Whether you will just have a grow room exhaust or two, or will also be exhausting your lights separately, you have to get that hot exhaust OUTSIDE of not only the room your grow room is in but preferably the home itself. And also have cooler fresh air coming in at proper cfm levels according to your exhaust cfm's.

I use open reflectors and simply directing my grow room exhaust outside of the home(at the very least outside of the room the grow room is in) there is half the battle. In warmer months you cannot re-circulate hot exhaust into the home, in the colder months you can.
If after directing your warm exhaust air out properly and you still have temp issues it would then be time to exhaust the lights as well separately. Next step after that a mini-split a/c, chiller and airboxes or some other cooling device.

So you have three levels. The first being free basically, just need enough ducting. The second being a fairly cheap option as all one needs is another fan, more ducting and of course air-cooled hoods/cool tubes. If you have to use the third option as well that's when it gets expensive. If in the warmer part of the country the third and final option is a necessity. If in a cooler region as I am I can get away with just the first option, in the warmer months in the past I have just turned the exhaust and intake power up, this summer I will be switching to air-cooled hoods and the second option of exhausting lights separately just so I have the option if I need it. If I was dealing with high temps more than 4 months of the year I would grab a split a/c.

Well, I'm living in Southern California so it's looking like I'm gonna need to start saving up for a nice AC. I actually have a pretty decent sized one that may get the job done, I believe it's around 10k BTU or something. That's a lot for two 1000 watters but not like I'm paying for it right? And also, I think that might actually save me a bit of electricity in the long run. I have a 4000 BTU AC attached to the grow room right now but I don't use it because I just don't think it can keep up with the fans, I mean it makes a difference but it never maintains the temps without having to stay on 24/7. I'm hoping that since the 10k BTU is more powerful that it will cool the air faster and turn off more often since it's cooling the room with ease instead of struggling like the 4k BTU unit.

If following the advice in your 2nd paragraph doesn't work then do you think my plan with the 10k BTU unit will work? Or will my inline fans just make the AC run inefficiently?

C02 isn't that expensive really.

$125 for the regulator. You can buy a cheap timer for $10 and set it to come on ten minutes every two hours or whatever. There are calcs that will get you into the ballpark.
The tank deposit is $100 and $15 to refill. I refill about every 30 days. So once you get the equipment.... $15 per month to increase your yields by 10%-20% is a lot of bang for the buck.

You will also have to reconfigure your room so that the light cooling system is isolated and the rest of the room is sealed. You don't want to suck your C02 out the light exhaust.

As for the A/C.

Mine is dual function as a dehumidifier as well. It hardly ever kicks on the actual AC with my system. The dehumidifying setting puts off enough cold to keep temps down.

Just open the door to the box.. It'll bring in fresh air and hot air will escape. With your exhaust venting outside you should be good. Easy and cheap.. 85* ain't that hot, your shit will be fine. Don't make it harder then it is...

I think that you have some error in the exhaust system, maybe not big enough passive intake holes? your passive intake must be big, much bigger than the fan size, 4x the size or more. curves in ducts diminish venting, try having ducts as wide as possible with small angles if you had to curve it. make sure that you are not intaking from the same area that you are exhausting into