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venting question

juniorgrower

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Does the exhaust fan need to be running when my lights are off?
 

orangesunshine

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not to cool the light, but it will help with air exchange thru the room
 

Hushpuppy

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It doesn't have to run all the time but many people who draw their exaust air from within the grow space will run them constantly so that they draw fresh air into the space all the time. This can be an issue if your space is drawing air in from the cold outside air. While the lights are off, if the air coming in is cold then the room will get too cold. I have this issue and actually have my inlet air coming in by my heaters which warm it as it comes in. :)
 

Grower13

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I run my 24/7......... have a carbon filter hooked to it for odor control in addition to cooling the light.
 

kiksroks

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Hushpuppy said:
It doesn't have to run all the time but many people who draw their exhaust air from within the grow space will run them constantly so that they draw fresh air into the space all the time. This can be an issue if your space is drawing air in from the cold outside air. While the lights are off, if the air coming in is cold then the room will get too cold. I have this issue and actually have my inlet air coming in by my heaters which warm it as it comes in. :)
What would be your minimum lights off and lights on temps?

We've had a cold snap recently and although mine draws through the light but from within the grow room, inside my house, it gets down to 67-68 with the light off and maybe 70-71 with it on. I've been considering shutting it off some during the day but my I keep my house at about 69 on the thermostat right outside the room so I doubt I would gain much.
 

juniorgrower

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Thanks for the quick responses. If I run it all the time will it help my plants flower faster and bigger?
 

orangesunshine

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juniorgrower said:
Thanks for the quick responses. If I run it all the time will it help my plants flower faster and bigger?
the more fresh air that you can exchange in the room the better---yes, they will grow bigger, faster, and healthier
 

Hushpuppy

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Yeah, having the fresh co2 coming in all the time definitely makes a big difference in the whole grow. I have had a difficult time with ballancing temps in my cabinets because of where they are is pretty exposed to the outside temps which have been swinging wildly lately. 60*f minimum temp and 80*f maximum temp for everything to do well, IMO, but I think they seem to do best if you can keep them steady between 70* and 75*. At least this is the case for the strain that I am running now. This White Russian is a very finicky plant that doesn't at all like changes.
 

juniorgrower

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As always you have been a great help HP. My new rooms that I am just about finished building are In my house that is kept around 65 degrees so hopefully I shouldnt be having the temperature problems that my original grow area had. The original grow area was in a non heated out building. It has been abnormally warm around here for this time of year or I would have had to change my growing area a lot sooner.
 
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juniorgrower said:
Thanks for the quick responses. If I run it all the time will it help my plants flower faster and bigger?
No, running the fan all the time will not help your plants grow faster or bigger. I do not believe that there is any benefit to running an exhaust fan while the lights are not on. The plants need a continual supply of fresh air all the time the lights are on for proper photosynthesis. I run a small bathroom type fan mounted near the ceiling to help maintain temps, but I do not run my large exhaust fan 24/7.
 

orangesunshine

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no comprende THG---are you saying there is no benefit to exchanging the air in the room when the lights are off???the plants shut down when the lights are out---they may not photosynthsize, but they will transpire and breath don't you think


just got done looking for anything that a plant does during the dark and find not much that would apply to our usage besides it won't grow without proper lighting---so---i guess the best answer in my case is---my filter is on the end of my light line and also cools the hoods as the room is being exhausted---if the exhaust fan were turned off with the lights my carbon filter would become inactive and that would be a no bueno---
 

Sixx

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juniorgrower said:
Does the exhaust fan need to be running when my lights are off?
That depends on your situation. Your temps are OK... Anything over a 15 degree change between Lights on/off will cause slow growth. Hushpuppy is right on, 70-75 is just about optimal in most cases.
Also, humidity typically increases at lights out with the cooler temps, which is bad news where I am, so my exhaust runs 24/7.
Your plants will use up all of the Co2 in the air around them in a few minutes.
If your plants run out of Co2 every night with the exhaust off and no constant air exchange growth will slow...Thats Another reason my exhaust fan runs 24/7.
Hope that helps.
 

juniorgrower

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CO2 is used by plants when the lights are off? When a co2 setup is used, does it stay on when the lights are off?
 
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No, plants do not use CO2 when the lights are off. The real reason for exchanging air is to cool your space and to provide enough CO2 for proper photosynthesis. I do not run my exhaust 24/7 and never have. Can anyone provide info (scientific stuff, not anecdotal stuff) that shows a plant needs air exchange during the dark period?
 

bubba902

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I'm with THG, I don't run my fan 24/7 either.. I'm not sure how low my temp gets with lights off, but with lights on they are 76-78F, with exhaust fan on 70F (still lights on). I'm probably going to have to add another heater in the room. or is 70 substantial enough for adequate growth?
 

Grower13

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jonath4n said:
I'm with THG, I don't run my fan 24/7 either.. I'm not sure how low my temp gets with lights off, but with lights on they are 76-78F, with exhaust fan on 70F (still lights on). I'm probably going to have to add another heater in the room. or is 70 substantial enough for adequate growth?

I bought a temp gauge from walmart......... gives you the high, low and current temp...... plus humidity....... cost around $5.00.
 

Hushpuppy

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Once again THG gets me on something I had not considered when I answered the air on question.:eek: Yeah the plants don't need the fresh air as much(if at all) during the dark period as they don't use co2 during the dark period. I do agree that I like to have the air flowing periodically to maintain humidity levels. :D

And if you want to get really technical you could run yer fan for 30 minutes after lights go out to completely cool them, and then run it again 30 minutes before lights on to fill the space with fresh air for when the lights do come on and the plants wake up. That's probably not a critical thing to do, more a matter of personal prefference.:)
 

orangesunshine

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Hushpuppy said:
Once again THG gets me on something I had not considered when I answered the air on question.:eek: Yeah the plants don't need the fresh air as much(if at all) during the dark period as they don't use co2 during the dark period. I do agree that I like to have the air flowing periodically to maintain humidi

true that---i wish she made house calls---lol---i do like the idea of constant air exchange no matter if the lights are on or off---am i wasting energy running the exhaust---probably as it relates to the needs of the plant, but then again---i think not as it is constantly cleaning the aroma of fresh ganja---:icon_smile:
 

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