The RH in my tent is hitting 92% with lights out during the day at 20.7 degrees. I moved it into a wardrobe where it went down to 66%. I then turned a fan on low & high & the RH went up to 77%. Can someone explain why? I thought running a fan helped move the air & keep it down.
Before the fan, your humidity meter was in a low humidity place surrounded by higher humidity. When you turned the fan on, it began to equalize the humidity everywhere, including the low humidity spot.
Great answer & thanks! So if my plant is in a low humidity zone, then its ok even if the surrounding area has a higher humidity?
I'd be a bit surprised by that, since humidity tends to be higher nearer the plant because of water transpiring from leaves. I use an oscillating fan to try to keep the humidity uniform.
I had the fan on the ground blowing up under the plant. Saying that I turned off the fan & it dropped but her leaves were wet when I took her out. I'll buy a dehumidifier this week. Thanks for the reply!
When lights go out, temp will fall, and humidity will automatically skyrocket. That can be prevented by some combination of increased exhaust fan speed and higher lights-out temp. Using a de-humidifier should be unnecessary unless the daytime humidity is above 70%. Cannabis loves high humidity, and following the Vapor Pressure Deficit chart will maximize growth. Subtract about 5 F from air temp to get leaf temp, then stay in the green. I have no bud rot problems in hydro with humidity in the high 60s during flower.
Thanks for the info!! My first grow I got away with about 60% as well during flowering. But right now its up to 92% with lights out & 20 degrees.
Yeah I know. I had it earlier in the grow. I keep wiping her with a damp cloth when she wakes up. I'm getting a dehumidifier this week
I see way too many people attempting to grow without a real functioning exhaust fan in the space ducted to the outdoors with a sealed duct. I use a 6" 440cfm fan for my 4x4 flower area and in the summer it runs on high 24/7. Don't turn it off at lights off and your humidity will stay a more reasonable level. I live in a very high humidity area. It's often above 95% humidity outside and it rains 3 out of 5 days on average here. My typical lights out humidity is 58-60%. Typical lights on humidity in the flower area is 38-42%. Right on point as long as you have good circ fans as well. Enough circulation fans will keep mold at bay even at higher humidity levels. You need both a dedicated exhaust fan preferably variable speed to control lights on temp, and a good circulation fan for the space. One can't do both jobs. If your garden is over 150 watts no way it will be healthy without an actual ducted exhaust fan.
I have a 100w Migro led & I just added a 200w red cfl. I leave my fan running 24/7 & my extractor reduces the rh by 4/5%. I only have a 2x2 tent. Im actually about to post a thread about wether I could get away with 1 plant under the 100w led. Im wondering is it worth my while?
Can you build a window vent or anything similar to duct the fan all the way outside? Possibly duct it to an already existing bathroom fart fan or kitchen oven exhaust? When you say extractor I'm assuming it's blowing out of the top of the tent and then short cycling back in after it's warm and moist without any actual ducting? Need a fan that blows outside to manage humidity levels well without a dehumidifier which is expensive to run/creates more heat.
This is only my 2nd grow so Im winging it!! So my extractor connected to my filter vents into the room my tent is in. I have plenty of acoustic ducting so are you saying I should have that air going out of the window?
Yes. The hot moist air from the grow space should get pumped outside. That will actually reduce your humidity especially at lights on quite effectively. It's just running in circles right now picking up more heat and moisture each time around and never being eliminated. The plants will be more happy too because when you pump the air out it gets replaced with fresh air for higher co2 and oxygen content in the grow space.
If you can connect it to an existing bathroom or kitchen exhaust duct/dryer that would be easiest instead of making a window vent. There is effective ways at making a window vent that can't be detected from the outside.
I have 50ft trees at the back of my house & I have my tent in the bedroom in the back so I was thinking of just putting the ducting a little bit out of my window when the lights are out. Do you think that would help? Sorry for all the newbie questions
It would help but a real window vent would be better. You won't be able to just have the window open year round. Check out the window vent build in this grow room. It's about 3 minutes in when it starts. It's a weird old video but the window vent build is awesome.
I really appreciate you taking the time to give me your help. I'll have a look at how practical that would be for me to do. I only rent so Im funny about making too many changes to the place.
It can be done much more simple if you live in a legal area and don't care about people seeing the duct in the window. I cut a piece of plywood about 1/4" smaller then the height of my window opening since it slides open. I only made it about 16" wide and I cut a 6" circle in it for the duct. I bought a 6" metal flange to screw to it for the duct to attach to. I put a strip of foam weather stripping around the outside rim of the plywood. I put it in the open window frame and shut the window tight on the plywood. It seals up against the foam. I then cut a few short pieces of wood to wedge the window tight against the plywood and prevent it from being slide open. I hang a dark curtain over it in my room.
I live in Alaska and it doesn't leak any more cold air in the winter then my normal window if you do the weather stripping tight and size the plywood correctly.
