Humidity over 80, lights out.

Second grow and looking for advice. I use a temperature controller to maintain my temps and the humidity is just fine while lights are on. When lights are out, my humidity jumps to 80%. No heat to remove the humidity in dark. What have others used to control humidity when connected to outside air? If I disconnect intake from window while lights are out, humidity only drops to 75%. New York winter is cold right now.

Setup:

Tent:
5 x 5 x 7

Lighting:
630w CMH (dual 315w bulb open fixture
600w HPS (Air-cooled reflector w/ dedicated intake and exhaust with fan)
300w LED (full spectrum)
45W LED (blue/red supplemental)

Venting:
Temperature controller utilizing 6" intake fan from window to blow cold winter air in and 6" exhaust fan to exhaust warm air out same window.
Hanging box fan on for 24/7 internal air circulation.

Plant Info:

Strains -
Blue Widow/Critical Sensi Star/Pineapple Chunk/Aurora Indica

11 plants, five in 10 gallon fabric pots, six in 5 gallon fabric pots. (Too many plants for this space) i know, but they've all been doing very well until this week. Planning on 6 plants in 15 or 20 gallon fab pots next time around! Now entering week 14 of total growth, week 4 of flower. Mostly organic soil, small amount of coco mixed in each pot with fox farms happy frog soil sunshine mix soil. Neptunes harvest and Dr. Earth organic fertilizers. pH adjusted water. Temperature controller used with outside air intake and outside air exhaust.

Some pics here:

Are you running the exhaust 24/7? Can you turn the exhaust fan up?

seems only logical fix would be dehumidifier if the answer is NO to questions above

If i leave my exhaust off during lights out my RH will go up to 80-90% aswell. But with my exhaust left running 24/7 on low setting i am able to control the RH in the tent at lights out, usually sits around 50% on low


I live in Canada, cold winters where i am as well

Diggs99,

If I run the exhaust 24/7, it helps with the humidity a little, but then it gets too cool inside tent. Just one fan running causes such a vacuum, that running only exhaust will draw cool air in from intake. Or the other way, just the intake on will suck too much cool air in and not exhaust enough cool air out.

The dehumidifier I have is old and bulky. It measures approximately 14" × 17" x 22" and I will have to sacrifice a plant for the space.

On the other hand, if I switch my intake to draw in air from inside my home, the air is not cool enough to keep tent under 80°F. I'm trying to avoid using an A/C in winter.

Unhook the intake from the window and use the air inside the room where your tent is. Keep the exhaust as it is and run it 24/7

ya i def see the dilemma

Your gonna want to wait for the more experienced growers to show up and help you out. I am still new to all of this myself.

I am just using the air from my laundry room/basement for intake, so temps usually stay a few degrees below ambient once lights go out. i keep my exhaust running 24/7

ApfelStrudel said:

Unhook the intake from the window and use the air inside the room where your tent is. Keep the exhaust as it is and run it 24/7

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I've tried this already. And while it works alright during lights out, my home air is too warm in the winter to cool the tent from heat generated by the 630w dual bulb CMH fixture. I cant find an air cooled dual bulb CMH fixture, to help remedy the heat from this fixture.

I forget what they are called but you want a ducting piece. I have seen them come T shaped and Y shaped. There is a piece that closes off the air from one to the other, or both open. It can be controlled manually or on a timer. I think I have even seen one controlled by temp before. Install it on your intake and have it so the air is from outside during lights on and inside during lights off.
Also where are you exhausting to? I am guessing just back into the room the tent is in?
IMHO your best bet is to run the dehumidifier. If your intake is coming from in the same room as the tent during lights off just run it outside the tent.

Cheers

GreenHighlander said:

I forget what they are called but you want a ducting piece. I have seen them come T shaped and Y shaped. There is a piece that closes off the air from one to the other, or both open. It can be controlled manually or on a timer. I think I have even seen one controlled by temp before. Install it on your intake and have it so the air is from outside during lights on and inside during lights off.
Also where are you exhausting to? I am guessing just back into the room the tent is in?
IMHO your best bet is to run the dehumidifier. If your intake is coming from in the same room as the tent during lights off just run it outside the tent.

Cheers

Click to expand...

Great idea! I'll start a mission to find out what it is and where to get one!! Lmao!!

I've considered dampers, like on a dryer exhaust. Let air one way but not the other. But if there is enough pressure inside the tent, it'll probably keep opening and closing them. This would surely minimize the humidity entering with the free flowing air. However, I'm afraid its looking like I'll have to sacrifice a plant for space to put the dehumidifier in the tent and add dampers to my intake and exhaust. I haven't tested just dampers yet, but playing it out in my head leaves me thinking that this situation won't be resolved that easily.

Your idea is much better, but what are those automated air valve things actually called? Lol!!

The dehumidifier I do have readily available is an Emerson Quiet Kool 40 pint with compressor. Its an ugly beast, but does its job well sucking water from the air.

The lights are running 12/12, on at 5PM and off at 5AM. I chose this schedule so the lights heat the cooler night air as the warmer day air has a lesser affect on tent when lights are out.

My intake goes straight from window to tent. Exhaust is the same, tent to window.

I had the same exact problem in a 5x5 tent. I bought a 200 dollar dehumidifier and problem solved. https://www.ebay.com/itm/Danby-Premiere-DDR060BDWDB-60-Pint-Dehumidifier/233097275144?epid=23023242698&hash=item3645ae2708:g:Zb4AAOSwO-hcP4p5

You want Ts inline, with dampers, on both intake and exhaust. Run fans constantly at reduced power during lights out, circulating house air. At lights on, change the dampers to outside air and run fans off the temp controller. You can get motorized dampers that could be tied to the light timer and you'll need a fan controller with multiple setting options.

Picked up another dehumidifier from a friend and tested it out this morning with no changes to my air intake or exhaust! This thing kicked RH's @$$!! Drop kicked humidity from 75% to 30% in just two hours on max!! I had to crack open the tent with lights out just to lower the setting before I left the house for work. Didnt have to sacrifice any plants for the space, just reconfigured the layout! Next purchase will be a humidity controller so this thing can kick on at specific RH levels and do its thang. Right now I have it set on a timer to operate opposite of the lights.

Now that I know I can drop the RH below 30%, has anyone experimented with low humidity to increase resin? RH should be around 40% for flower, but will slapping these girls with 30% or lower at times help increase resin?

Thank you everyone for your help so far! I'm too new to like any replies yet!

Trich-o-matic said:

Diggs99,

If I run the exhaust 24/7, it helps with the humidity a little, but then it gets too cool inside tent. Just one fan running causes such a vacuum, that running only exhaust will draw cool air in from intake. Or the other way, just the intake on will suck too much cool air in and not exhaust enough cool air out.

The dehumidifier I have is old and bulky. It measures approximately 14" × 17" x 22" and I will have to sacrifice a plant for the space.

On the other hand, if I switch my intake to draw in air from inside my home, the air is not cool enough to keep tent under 80°F. I'm trying to avoid using an A/C in winter.

Click to expand...

Why does it stay so warm during lights or if you're circulating the air?

Why is 80F a problem during lights out as long as it keeps RH down?

ttystikk said:

Why does it stay so warm during lights or if you're circulating the air?

Why is 80F a problem during lights out as long as it keeps RH down?

Click to expand...

It gets so warm because of my dual bulb CMH fixture. Its open and puts out about as much heat as a 600w HPS but performs better than 1000w HPS.

80F is a problem, when lights out, because RH hangs at 80-90% with only an internal circulating fan. Mold and powdery mildew love that environment.

---Update---

Humidity held between 30-35% for 11 hours during lights out with old dehumidifier!! Now I have to screw with it a bit to hold at 40%. Is 30% RH alright? When lights and cooling fans on, it fluctuates quite a range from 40% - 80+%, because of the outside air.

Lights turn on, lights heat up air, cooling fans kick on at 80°F, cooling fan introduces cold outside air into tent, humidity rises to 70%+/-, temp control stops cooling fans at 68°F, with venting stopped lights heat air and reduce humidity to 50%+/-, cycle repeats until lights off. When lights off, dehumidifier kicks on to dehumidify air to 30%.

Max setting on dehumidifier brought RH from over 80% down to 30% in only two hours. I turned dial from max 10 to low 3 and its still a bit much. Didnt drop below 30%. Will test lowest setting tomorrow, in hopes to get RH to hang at 40% with lights out.

Very easy fix if you can afford it - just put some oil heaters in your room. Put a standing fan in front to blow the warm air over the plants at lights off. I leave mine on 24/7. Humuidy never goes above 41%. Ambient humidity outside is high 90%s

slinkysaurus said:

Very easy fix if you can afford it - just put some oil heaters in your room. Put a standing fan in front to blow the warm air over the plants at lights off. I leave mine on 24/7. Humuidy never goes above 41%. Ambient humidity outside is high 90%s

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I use a 5x5 tent and my floor space is pretty limited. The dehumidifier is working fine so far. But it still takes up the space of a plant. Does the oil heater dry out your soil or heat the roots up? I also use fabric pots. So, Im trying to avoid adding heat to reduce RH. Oil heater might actually take up even more space, if the plants cant touch it.

Trich-o-matic said:

I use a 5x5 tent and my floor space is pretty limited. The dehumidifier is working fine so far. But it still takes up the space of a plant. Does the oil heater dry out your soil or heat the roots up? I also use fabric pots. So, Im trying to avoid adding heat to reduce RH. Oil heater might actually take up even more space, if the plants cant touch it.

Click to expand...

Glad you got sorted. No it just keeps the humidity in the room at a reasonable place. Especially important during flower. I also run a dehumidifier from my intake room. I need both for my humidity to stay stable! You're most lucky!

slinkysaurus said:

Glad you got sorted. No it just keeps the humidity in the room at a reasonable place. Especially important during flower. I also run a dehumidifier from my intake room. I need both for my humidity to stay stable! You're most lucky!

Click to expand...

Inkbird has temp controllers and humidity controllers for about $40-$60 each. I have the temp controller to activate my venting/cooling fans to maintain a constant temp between 70 and 80. Although, I should drop the settings a few degrees to mimick cooler fall weather. I'm going to buy a humidity controller next. So, i can pull my dehumidifier off of a timer running for 12 hours and allow it to only kick on when needed, in an attempt to become a little more efficient.

What kinda heat is the dehumidifier adding during lights out? Mine will raise my 4x8 drying closet 5-10F in a couple hours, even with constant ventilation. I run it on a temp controlled switch so it doesn't overheat the room and cook off terpenes.

And why are you letting your tent get up to 80 before venting? I'd bet the 12F +/- differential swing, coupled with rapid cooling when vents turn on, is gonna stress your plants. Plus, you'll lose terpenes in late flower being that warm.