Hi everyone, Where did I go wrong on this build? I have a 30 square foot wooden box with 2 growing areas. In the smaller room I have a 2" passive intake and a 2" passive exhaust going into the flowering section. In the flowering section I have another 2" passive intake along with the 2" passive intake coming from the clone section. See diagram below. My system exhaust is a 4" 192 CFM fan that seems to really be pushing out the air. Though the temps in my place are 75-80 degrees, The temps in my box range from 92-96 degrees. At this time I am only running six 42 watt 6500k CFL's which doesn't seem like it should be a lot. I think that there must be a basic design flaw in my box somewhere. This is my first build but I just wanted to grow very small amounts for myself to help control seizures. How can I get these temps down? Do I have too much/ too little passive intakes? I am at a loss. ANY help is most appreciated. Thank you for your time.
Hey Jellyman, Thanks for your interest. Much appreciated. I am taking digital temp readings from the bottom of the cabinet, near the plants that have just sprouted. I don't have a lot of hope for these plants long term health unless I can get some lower temps soon. I'm almost sure that it could be my intake/exhaust ratio but am not ready to cut into my finished cab just yet on a hunch. I need the expert advice of all of the pros out there. (Note to self and others; don't EVER EVER begin to germinate seeds again until new cabinet has been fully tested.) Hope your day is going well so far Jellyman. Thanks again for your interest.
I have 24 sq in open for a 160 cfm and it still sucks the door closed, which means I'm getting plenty of negative pressure. I use a 250w HID and get 6-7f above ambient. You have 6 sq in open for 192 cfm, and you're getting 20f above ambient, with the same wattage in cfl. I believe that you can open more intakes without killing your negative pressure, and that it will help your temps. Also, like Jman suggested, take temps in different areas of your box and make sure you have plenty of circulation in there.
Is your intake up high(top of box)? You should be drawing air in at the bottom of the box.. exhaust at the top..
@notsure Thanks for the advice. I think that I will open more intake as you suggested. It hurts to cut into a box that I thought was finished though. Right now I have three fans stirring up the air and it is helping some. I also earlier tried putting a large bottle of ice in the cab but it melted pretty fast. I have taken temps in different places and the lowest temp was at the top of my cab. Not sure why that happened since I figured that heat always rises, even in my design. I have my cfl's pretty low right now since I have 3 day old plants. They look pretty happy with all of the light but I worry about the stress that they will suffer when the heat gets really bad out here in the southwest. My plan was ultimately to use my six 42 watt cfls in the smaller clone section of my box and use a 150 watt HID in the larger flowering section to get some type of scrog perpetual grow on a pretty small scale. I don't know that I will be too successful though since I already have heat issues just using the cfls. I also wanted to keep this grow very stealth but that is going to be pretty hard with all of the fans, etc. @basssnob Intake is on the back side/bottom left of the cab. Exhaust is on the back side/ right top of the cab. I do have a 2" intake from the smaller section going into the larger section which makes it all somewhat confusing. I appreciate all of you guys taking the time to help out a total noob to all of this. I've read a lot on this forum and I knew that this was the place to come for help. Thanks again to all who help.
I'm pretty certain that the passive intake is supposed to be twice the size as the forced exhaust. Personally I would put another 2" hole in the far left side of the clone area and a 2" hole in the the far right side of the flowering area. Either that or double the size of each existing hole. I have 8 23 Watts in a small space than you and the only real difference is that I have more passive airflow.
That sounds like a good plan, I like your box too. I'm all about DIY too, keeps costs down and gets the job done. I vegged with cfl for 2 years, but the cost of replacing bulbs and the efficiency of MH convinced me to switch. The only cfls I use now are (2) 14w bulbs for rooting clones, but I had a lot of fun building my own diy boards and they grow some nice plants. Yea, I get lower temps at the top of my boxes as well, despite excellent circulation and airflow. I think it's radiant heat from the bulbs, I remember from HS that heat is transferred in 3 ways, convection, conduction, and radiation. The fans take care of convection and conduction, but radiant heat will still be there. That's my conclusion anyway, I could be wrong. Good luck and have fun!!
I just skimmed over the other replies so forgive me if this has been mentioned. Your fan is pulling air through the flowering area but not the vegging area. There's nothing preventing the air from going in through the flowering intake opening and straight out the flowering exhaust. If you want air to be pulled through both areas, close the flowering area's intake. You'd be better off with separate fans and intakes for each area. When using PC-type fans, there should be one on the intake as well as the exhaust. Only with a good centrifugal blower should there be just one.
Thanks again to all those who offer suggestions. Its what makes this forum work and it really helps those, like myself, who are stuck with something. I have my little plants out of the cabinet right now and they are growing under cfl light on a counter where it is cool. I plan on starting work again on my cabinet today after work. My plan initially was to take everyone's advice and open up more passive intake area but I am still not yet sure as to how much or where. It seems that there is no real consensus or formula to all of this. Some people say that you should have only slightly more passive than active openings, and some people have had more luck with quite a bit more passive than active openings. Everyone does seem to agree though that there should be more passive area than active area. I think that what I am going to do tonight is to open up a small amount here...and a small amount there, and then just see what happens. I think that I will begin opening up the smaller clone/vegging area first since the point is to get the air moving throughout the cabinet. @Jellyman, I see your logic. It make sense. However, when the cab is running as it is now, I have a large amount of negative pressure on the intake into the vegging/clone area. This makes me think though that it might just be better for me to open up ALL of the extra passive holes in the vegging/clone area and then just close off the passive opening in the flowering area.. As far as having two fans, that is not practical since I am trying very hard for stealth, and the one fan I have is already too loud. Two fans though would work pretty nice, and it would help out a lot too, no doubt. @ Notsure, I looked at your set-up and I was very impressed with what you have going on. I esp. liked your "scrog rack." I think that eventually, if all else goes well, that I might try to build something along those same lines. It seems like a pretty practical way to keep your plant stabilized while still being able to remove it to work on it. You've got some mad design skills. So, my plan is to close the flowering areas passive opening all together. Then start opening more passive area in the clone/vegging space until "something clicks." I assume that I would also need to open the same amount of passive area between the two different areas of the cabinet. I'll start on it later tonight and report back if it works. Thanks again to everyone. OK, Going to put a last word up on here now so that anyone else having the same/similar problem can maybe find some direction from this post. My problem was that I had way too few passive openings. I almost tripled my passive openings all of the way around the box and it brought the cab temps down to a few degrees above ambient temps. My mistake was in thinking that since I had a 4" fan as exhaust, that I needed 4" worth of passive intake. My solution was to keep opening things up until the temps stabilized and yet still allowed me to retain some negative pressure. Thank you again to everyone who advised me on this. Cheers!