Humidity Too High for my late flowering Autos

Hello there,
I’m new to the club and also a beginner grower. I am having the same humidity problems. Before I ask the question, here is my setup:
4x4 tent set in an old stone basement with dirt floor and without environmental control. The basement is typically at 54°F (spring-summer) 40°F (winter) and humidity at 70% sometimes the humidity drops to 54% I guess based on outdoor weather.
I have two VIPARSPECTRA Dimmable 600W Full Spectrum LED Grow Lights, three small oscillating fans set on the corners blowing at the canopy level, and two small fans blowing on the floor, I have an exhaust “Active Air 6-inch 400 CFM Fan with 6" Carbon Filter. The exhaust fan works 24/7 which it is the only way I have been able to keep the humidity at okay level sometimes based on the VPD charts I have seemed online. As intake, I have run an 8” ducting that takes air from the outside of the house and not from the basement.

I have four autos (two super skunks and two blueberries) they are mid-flowering perhaps almost at the end of their lives and I am about to start flushing them.

Having said all that, I am having trouble to keep the humidity below 59%. Adding a big dehumidifier is out of the question since they are very expensive plus, I have read about so many people buying them to then later find out that it did not make any difference to their environment. Also, I would think I would need a very large equipment since the basement is about 2,300 Sq. Ft.

I am afraid that the humidity will damage the precious buds that are growing bigger by the day.

Is there anybody out there who could give an advice or someone who has been in the same situation and the outcome was positive?

Thank you,

Go to ebay and check out some of the factory refurbished ones. You can find 70 pint LGs, Fridgidaire, etc for like 150 bucks


Dehumidifier will eventually be in order. But that humidity(59) isnt a disaster tho. Keep the air moving with fans and let temp stay in the 80s. That will help prevent bud rot. Your on the ragged edge tho .

Thank you for the information. I think I will definitely look into getting a dehumidifier.
Overnight, the humidity went down little by little (57%,55% to 52%). This morning the humidity in the tent went down to 45% and temperature at 75°

I have about 1900 sq ft basement it isn’t dirt floor but concrete and I have a hygrometer located outside the tent and in the adjacent room to monitor the RH/temps and based on what they are will adjust the incoming air into the tent room and tent by opening or closing door and or vent flaps into tent to change humidity. Depending on what the outside RH is for you you might consider looking at what inflow of air is best and may find removing the 8” duct pulling air from outside and using inside replacement air is better? I don’t know but it is a constantly changing thing based on outside environment.
I also do need to run a dehumidifier depending on outside and adjoining room/s. Is your basement all open or are there rooms?
Increasing temps will lower humidity in the tent.
Increasing or decreasing my inline fan speed also helps me regulate environment and will lower it if I’m drawing high humidity air which also will raise temps and lower humidity in tent…took awhile to figure out what works best based on ever changing seasons etc.
Just some thoughts.

Thank you for the feedback!
At the beginning during germination and early veg, I had the 8"duct inside since the humidity in the basement was 78%. As soon as I saw the pre-flowering stage,I tried to lower it but I wasn’t able. The only way I was able to lower it to the high 50’s was by directing the 8"duct to the outside. Then, I encountered another problem when the outside humidity increases.

The basement is just one room with an adjacent crawling space.
So far I have been able to keep the tent at 44% humidity and Temperature at 75° running the
exhaust fan at high speed 24/7. If I lower the speed to Medium or Low, the humidity goes over 62% and the temperature over 87°.

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Sounds like you have things figured out (subject to change…outside weather…lol) for getting veg and flower environment in range. Good deal!
It can get crazy.
Running 2 rooms 4x8 tent in each. 1 tent in flower and 1 in veg.
Flower room dehumidifier running almost 24/7 keeping RH 50 or under pulling 3 gallons Or more daily
Next room in veg running humidifiers using 3 gallons or more daily
These 2 rooms share a door between them. Both these are being vented into a third room and that opens into the main room and straight shot to staircase…hot air rises cold air sinks…temps increase RH decreases…temps decrease RH increases.
Main basement room 75% Rh currently and a door opens to veg room from there. Playing with 3 doors (one at top of stairs) adjusting temps in house, dehumidifier, humidifier, in line fan speed, light schedule, watering As early in day as I can if in flower and outside conditions all can come into play.
It can get crazy…haha

Are you using a carbon filter? If so make sure the prefilter isn’t dirty…slap it with fan off and see if it dusts up. If so needs washed. I just hand wash it in the utility tub with some liquid soap and warm water and wring it out and hang to dry. Also by removing it you can check if efficiency increases while it dries. Unless it’s an issue with smell for awhile even unhook the carbon filter and see what temps do at what speeds…
Always good to know how they work on their own this way you will have an idea when one part or the other is clogging or used up.

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