Extream humidity

I have a problem with high humidity in my flower room (up to 99%) and for the last year I did not find a solution, Today I turned my exsute fan off and humidity is perfect.
My question is how bad Is it? Dark time with no air exchange, i have 4 fans in the room so the air is moving good, I am worried about low O2 levels,
And if this is not good for the plants I was thinking of using a digital timer to turn it of and on every hour or so for few min , is that a good idea? , and how long should I turn it on cuz it is extremely humid out side, the room is 2mX3mX3m and my exsute is 800. Thanks

If air is moving inside your room, as it’s not hermetically sealed, IN THEORY there should be some air exchange from “outside” so I doubt a lack of oxygen would be an issue

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and turning on the exsute fan 5 min every houre or somthing like that, good idea ?

I would be tempted not to do that, the constant start/stop will not be nice on your fan and you could destabilise things by suddenly sucking in so much humid air. I mean, what you would be doing is spiking the humidity every hour and by the time it settles you’re spiking it again, hardly a stable environment and, well, you wouldn’t be happy if I shut you in a room and did that to you.

So I’d be tempted to not run the fan if things are stable, but keep a VERY good eye on the plants to see if they stay happy, especially as I run things in a similar sized space but without an exhaust sucking air out, just good circulation in the room and use these cheap dehumidifier packs you get for rooms where, for example, you have a clothes drier. But I only do two plants so I don’t have massive transpiration from a room full of green from wall to wall.

Oh, where does your exhaust vent to? Just outside your grow space or do you duct it so it blows outside your house/shed/whatever? The reason I ask is that if you vent into the same space as your “intake” then all you do is circulate that same humid air and increase the humidity. You would either need to exhaust into a completely separate area, ideally outside, or you need to dehumidify the air going in

first thanks alot for the info and the quick reply !!
i have 50 plant from wall to wall so…
and i have my exhaust blowing air to the out side via carboon filter , where i live next to the beach and it is , as i said extreamly humid. and i have a small fan that brings air from the out side ’ but it was allways off in the dark cycle , and i was geting a passive aiir in .
like i said there are 4 12-14 inch vent in side.
my onlly worry is about the o2 %

Consider Air conditioning, it lowers heat and humidity at the same time.

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Or have a BFO dehumidifier to do the necessary before the air enters the grow space.

I do use AC and i have a hemidifier both dont help while i turn on the big vent,
i tried to get air using only a smalll vent and the humidty rise to 60
so is it btter 40 % with out any active air circulation or 60 % with small 9 inch vent?

and also what are the signs for lack of O2?

The place you need the O² is in the roots, and the usual cause of an O² deficiency there is drowning the plant which results in death. As long as your roots are healthy, then I do not believe you would have an issue due to the possibility of a minute drop in oxygen levels in the air overnight.

As I said, your grow space is not a hermetically sealed airtight space, there will be passive air exchange due to the air movement in your space via the vents you have, don’t panic and watch for any signs of any deficiencies such as changes in leaf colour. No change means everything is fine, and I don’t think you will have an issue.

ok thanks!
finaly my room is ballanced!
i hope it ok to ask another Q which is not related to enviroment control ( or may be it is)
my gorw cycle is that i have 48 plant and give them 8-9 W of veg inculding clone time i will take the clones from the plant that are going into flowring i veg the in a 2 L 1/2 a gallon pots for 6-7 W before moving them into bigger pot for flowring ( i do that for space reasones )
how bad is to let them veg in a 2 L pots they look great and when i move them into biger pots the roots system i really full

I would transplant up sooner, personally, but, again IN THEORY, if the root system is healthy the roots will happily grow to fit the new pot.

Dehumidifiers are air conditioners that smother themselves producing the unwanted waste byproduct of “heat”

Temperature control becomes more and more critical under higher kelvin or HID. With low heat emitting LEC and ground cooling in say a basement, a dehumidifier may work, but in the end it’s exhausting it’s heat within the zone, AC condensers are using outside air to exhaust the heat produced by the same principles as a dehumidifier.

In healthy dense flowering environments the plants, planters, and hydroponic solution continue to perspire (but less) during the dark cycle, in which case the AC will create a cold “dank” environment creating the need for a heat source to drive the humidity out through the AC working the maintain the proper temperature.

This environmental heat/humidity control system will eliminate the chance for any passing mold spores to take root in your drippy wet sticky buds and gives you more time to finish them, and time to fatten up!

Some growers use passive water supply to cool their environment, The best system is using well or thermal field with a heat pump (geothermal). I’m thinking about going geothermal with my passive water supply, well, field, or whatever one you can guess I have.

Where does your fan vent to and draw air from?

If the dehumidifier is in the tent/room, then yes regarding heat. But I was talking about dehumidifying before the air enters the grow space if possible, a slight difference. And it also depends on the dehumidifier as you can actually buy models which have a nice duct to vent outside whatever area you are in.

Oh, and a higher Kelvin light, say 6500K, does not run any hotter than a lower, say 2700K, one.

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I did not know that…

Now I can put dehumidifiers on my list of efficiency and feasibility! (one more trick in my bag of tricks) Thanks!

P.S. Humidity is a bud’s worst enemy! Only a flame thrower can do them in faster!

Here’s precisely what I mean



99 % humidity guaranteed bud rot in last couple weeks of flower , you got to get it down to 40 %.

this is my 4th grow and till now hadnt hade bud root, 99% was not all the time 70-90 was the avarge, but i have 4 vent that keep the movig alot?

#bigbananafeet how to you calculate the size of dehumidifier needed for 3X2X3?
so now my humidity is good but the room temp is 20 C or 68 F ,how bad is that?

For size, see the manufacturer as every dehumidifier is different, you can’t just say you need “x”.

And temperatures? That is strain dependent with some being happy all the way down to 10°C. But 20/68° shouldn’t be an issue, if it gets up above 30/85° then that’s more of an issue needing a LOT of air movement to prevent mold, etc.