a couple venting and cooling questions

Hi everyone, I have 2 rows of 5 600w hid lights. I have a carbon filter at the beginning of each row then a 10 in. 700cfm fan then the 5 air cooled hoods in a row then vented outside. I am thinking of moving the fan so it is just before the outside exhaust hole or should I just add another fan? Would it also have to be a 700cfm fan? Also do I need to put a speed controller on my fans? What is their purpose? I am also thinking it might be a good idea to put backdraft dampeners in the ducting to keep bugs etc.. from coming into the room when the fans are off or would they restrict my airflow. Also just read that it is not good to draw the heated air from your lights thru your fan. I wouldn't have thought this would be a problem. I also have a 3ton A/C unit in the room. Thanks in advance

a fan speed controller is just that, it controls the speed of your fan. What purpose? More or less air flow. Leave your fans running, especially in flower. Having them turn off with the lights isn't the best idea in flower. No airflow = more likely hood of mold. Yes running the heated air through the fan isn't the best idea. The bearings in the fan may not be rated to handle the temperature. I had this problem and the grease got too hot and started leaking out of the seals causing the bearings to go bad.

I was going to turn off the fans when the lights are off (at least in the winter) because I live in a cold climate and didn't want to draw all that cold air into the room. I was thinking of having a 20 pint dehumidifier running when the lights and fans are off.

Just a thought and maybe I am not understanding, but isn't an exhaust fan suppose to draw hot air out of a room? (Could use one the size of a mountain in Washington, D.C. LOL)
Also i would leave fans running 24/7 for movement....keeps mold down and strengthens the plant...so I've been told.

Nice set up!!! What are you growing?
Good luck!!

I have 6 wall mounted fans for air movement (12x24). If the inline fan is mounted before the lights it will push the air thru my lights but I have heard it is better to draw it thru.

few things here for one yes you are going to want to put the exhaust fan right before the exhaust hole so the fan is pulling air through the lights rather than trying to push it through them. the problem with pushing air through is if there is a little leak anywhere in the ducting it will be forcing hot air into the grow room where if it was sucking it would be still removing air. another thing is i personally dont like running more that 2 lights consecutively in a row because as the air passes through the first light it is warmed up quite a bit meaning its cooling power is dropped per every light it passes through so twords the end of the line the lights are so hot they are not even being cooled at all. try to split them up a bit more and im sure your room will stay much cooler.

drgreentm said:

few things here for one yes you are going to want to put the exhaust fan right before the exhaust hole so the fan is pulling air through the lights rather than trying to push it through them. the problem with pushing air through is if there is a little leak anywhere in the ducting it will be forcing hot air into the grow room where if it was sucking it would be still removing air. another thing is i personally dont like running more that 2 lights consecutively in a row because as the air passes through the first light it is warmed up quite a bit meaning its cooling power is dropped per every light it passes through so twords the end of the line the lights are so hot they are not even being cooled at all. try to split them up a bit more and im sure your room will stay much cooler.

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I would say this makes sense but could possible be Solve with a bigger exhaust fan. Im now running a 6in for 2 600w, I know i will get a 10 in when i add my 3 light, possibly run a 12in. Possibly look in to the max fans man there 10in is rated at 1019 cfm

drgreen is correct all the way. My set up is filter, 600w MH bulb in Supreme air cooled reflector, 600w HPS bulb in a Supreme air cooled reflector out to an exhaust hole with a 6" canFanHO pulling the air through and exhausting it....there will also be a Danby portable A/C in the tent and a humidifier. It's a GL240 good size tent with movement fans.
What are you growing? I'll have a 4 plant perpetual harvest using a GL145 tent to veg 4, 4 under the MH, and 4 under the HPS. The big tent is the 12/12 tent.
Good luck!!

Just ordered 50 Kush clones today. Growing them in dirt. If I am exhausting my heat out of the building i can only have 2 exhausts because I can't put any more holes in the building. That is why I have 2 runs of 5 lights each. I have ordered an inline hepa filter for the intake but what do you guys use on your exhaust to keep out pests when your fans are off?

jakeman12 said:

Just ordered 50 Kush clones today. Growing them in dirt. If I am exhausting my heat out of the building i can only have 2 exhausts because I can't put any more holes in the building. That is why I have 2 runs of 5 lights each. I have ordered an inline hepa filter for the intake but what do you guys use on your exhaust to keep out pests when your fans are off?

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at home depot they sell these things that are made to put on the outside of a house for venting stove hoods out a wall, they have a housing over them so water cant get inside and a little door that opens and closes when fans are on and off. they make them in 6" and can be painted the color of the building and are real inconspicuous. that would not work for a intake but will work great for exhaust, when i had to pull air from outside i built a sealed box inline with a carbon filter housed inside that scrubbed the air before entering the room, nothing would get passed the filter. here is a pic of what it looked like just some plywood and silicone to seal it up.