High night time humidity

[mrmiyagi420]

Hi fellow growers. I have a 5x5x8 grow tent in my basement with three plants fast approaching late flowering stage (my fourth was male). I have a Spider Farmer 4000 LED. I have a 400CFM fan exhausting directly out of the tent and basement. The ambient basement temp is 70f and RH 55%. During the 12 hours lights on the tent temp stays at 78f with an RH of 45% using a 23 pint Noma dehumidifier. Everything works well until the lights go off.

The RH shoots up to 58%-65% when the lights turn off. (I can get the lights off tent temp to 66f-70f depending on outside temps - I'm in Canada) I've tried two types of 50 pint dehumidifiers (Frigidaire and Midea) Both of these blow the lights on temps into the high 80f's and keep it at 75f-80f during lights off. I added another 200CFM exhaust fan with no resulting change. I have oscillating fans going. I'm really not keen to add an a/c unit to my set up. Any other ideas/suggestions for reducing my lights off RH would be welcome. This is my first time growing in a tent. Thanks in advance for your help.

[Puglover1]

Is your basement usually dark during lights out? Maybe open a flap? If the fans are hitting them right it might not be an issue. My first grow was 3 plants stuffed into a closet, no lollipopping, not enough defol. Some mornings I'd see 65% RH but I never had any problems. Hopefully an OG will weigh in.

[mrmiyagi420]

Thanks Puglover1. Yes I keep the basement pitch black unless I'm in there. The basement is vented with house air or external air, depending which is coolest. I'm really baffled by this predicament. It's also been very hot here in BC which doesn't help. We'll see what anyone else can suggest hopefully.

[Puglover1]

You don't want to dehumidify during lights on, higher RH lowers the temp. The lights' heat dries the air out more. Have you tried leaving the tent open at night in the dark? It might let some moisture get out. It's been hot everywhere, I'm fighting to keep temps down and RH up.

[oldjarhead100]

I grow in my cellar but not in the summer because of whats going on with you ,my grow room is 7x10 I run 2 630 cmh lights I also have 2 6 inch discharge fans I ran one normally but the other I ran on a timer I used a heat and RH monitor that kept a 24 hour record .I have a 70 pint dehumidifier that kept the RH down and the second fan kept the heat down , Leds will certainly be able to lower your electric bill but will they provide enough heat in the winter ,good luck

[mrmiyagi420]

Thank you

[JuanHondo]

relative humidity tells you how much moisture is in the air compared to how much it can hold. warmer air can hold more than cooler air. the total moisture in the air stays the same, but when the lights go out, the temp drops, the amount of moisture the air can hold reduces, and RH goes up. you will always observe higher RH at lights out unless you have a dehumidifier or heater running. i don't know if this helps with your problem, and maybe it's obvious...but, that's what's going on...

[mrmiyagi420]

Thank you

[SoOrbudgal]

Yep that's correct from my experience with humidity good call JuanHondo, nice seeing your post.

[JuanHondo]

hasn't been an issue for me...just keep the fans running

[bboyfromwayback]

I live in the south eastern US. It’s humid AF all day, once the sun goes down you can literally see the air. Everything outside gets wet at night. My basement isn’t much better. I run a dehumidifier 24x7 about 7 months out of the year. June through September I’m lucky to keep the humidity below 52 lights on growing under LED’s. With HPS I had no issues but it got hot AF so I ran I portable ac unit as well. Now I don’t use the ac hardly ever. Lights off humidty gets into the mid 60’s. As long as you don’t let it get crazy high and have plenty of air flow you’ll have no issues. I have 5 fans in my 4x4.

Trade off, it’s the perfect environment to dry/cure in

[mrmiyagi420]

Thank you

[bboyfromwayback]

No problem! Airflow and strategic leaf removal is key. Another thing I’ll add, vent your tent outside if possible, not just into the same room or even another room in your place. It makes a huge difference. Otherwise you’re just recirculating that same humid air

[mrmiyagi420]

Yes I'm doing all those for sure. Cheers!