Cannot get humidity down below 70% with lights off PLEAASSE help

Urrgghhh still no better, high 70% nearly 80 RH with extraction on and 2 clip on oscillating fans, a tray full of silica crystals, 2 dehimifying pots a dehumidifier bag in the intake ducting and a small 500ml dehumidifier along with a small oil heater…no change!! So frustrated, never had this problem before and NEED to switcj to flower ASAP due to space between tops and light…at a complete loss =-(

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Help, humidity ranging 70-80°


Aug '17

Environmenatal Control & Issues
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Sounds like you’re going to need to upgrade to a big dehumidifier. Something like this or maybe bigger.

What type of lights are you using? Do you have a dehumidifier that can control humidity for the entire room that the tent is in? Im saying so due to i had Horrible humidity problems when hurricane harvey went thru. Only way i could get humidity under control was to buy a dehumidifier large enough to do entire room.

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I am running 600 watt lumii adjustable HPS, 1.2 by. 2m tent, I do believe I am going to have to invest over £100 for a big dehumidifier but wanted to avoid this as its getting very expensive! Need to top my plants very soon to control growth but the info on white chronic says not to top and leave main cola for best results =-/ theyre looking. So great I dont want rot in flower =-(

This is during lights off BTW guys, lights on RH is good, can I put my small oil heater inside thr tent at all or will that cause stress? Heating the room outside hasnt seemed to do anything.

The bad part about high humidity is it will take the larger one even if you have to put it in the room rather than the tent. The good side of the bigger one is that you’ll only need it when humidity is high and most the bigger ones give you the option to set a humidity level so it isn’t running full time. And it’ll last for several years if you buy a good brand.

Can I suggeat opening your tent?
I doubt rh is 80s in entire house?

My guess is that the heats causing evapotransporation to occur at a greater rate due to intense lights then when they are off it re condenses down due to temp drop. I have similar issue in high desert in crops what with the water being pulled from leaves.

I could open.up.the tent but worried about light from outside, I do have a roller blind over window in the room to hide tent from prying eyes, but cannot blank out light from the hallway…not such a problem in veg but during flower no light allowed =-/ plus they only have 6 hours of lights off right now…soon that will be 12 which will make my problem worse surely?

Can I ask…would having my central heating kick in.just n4 lights out help at all…strange as I see that high heat can.raise humidity…but being told a heater can help??? But then when.lights are on the temp rises to 26-28 and humidity drops to 45-60 which baffles me…if heat causes high humidoty how come the lights cause temp to rise but humidity to drop? I know I sound stupid but I am dealing with PTSD and my brain isnt at 100% functionality sadly. Thanks so much for the advice…i will be buying a large dehumidifier next week on pay day.

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Just open your tent…you are controlling light cycle, so who cares about the additional light from outside. If anything you get more light.

If you for some reason have your light cycle occurring opposite nature…well fix it :slight_smile:

You basically have a huge water source in an ez bake oven and aee trying to keep those planta from drying out inside the oven meanwhile its sittin there dumping water in the air.
Where are you getting intake air from? Exhaust goes outside?
What is theRH of your house? Do you have double pane windows in the weed room? What is your main source of heat for the rest of the house?

Central heating for house on a timer, yes my lights come on at 7pm and go off at 1 pm following day…can I just switch this around safely while they are in veg so that I can open.the tent at night time when.lights go out?
My extractor is vented by a window, in take is from hallway, it was the other way around until earlier today…not made any difference really…

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Double glazed windows, I do not have another hygrometer other than in.the tent…will order another now on amazon.

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Just got the 2nd msg about heater types.

If you use propane heat in your house without exhausting the gasses outside, a direct vent model, this is 100% your problem.

If you use wood fire as heat it will be not likely to cause an issue.

The reason most heaters actually raise humidity is because the main byproducts of combustion are carbon, oxygen, and h20 (water.)

Propanes main byproduct in high efficiency units is water.

This next one is harder to grasp.
The reason you get higher RH in warmer temperatures is because the air molecules have a greater potwntial to hold moisture in the air.
This is why temperature is soooo important for RH and not many people go into it.
50% RH at 50 degrees F is not the same amount of water in the air as 50% RH at 90 degrees F, it is way less. I cant really explain it more simply or in depth without making my eyes cross. Just know that in actuality you have been fooling yourself by going only by RH.

Found a nice table to demonstrate.

Temp. Water holding capacity of vapor in grams
50c. 88
30c. 27
20c. 14

As you can see the holding capacity is not a lineqr function snd is actually a bell curve. Meaning the rate of water holding capacity does not increase evenky with temperature, it exponentially holds more moisture.
Talk from anyone from alabama or brazil they will confirm hot does not reduce moosture in air…it makes it horrible.

You can flip your light cycle just leave them on the extra time until it is corrected. They can handle 24h of light for a day.

My immediate solutions recommendation would be to open tent up to larger air space, REDUCE temperature of room to retard the vapor holding capacity of air around your plants, and drop the cash for a large capacity dehumidifier.

I use the model kstad308 by keystone it works for 350sqft and pulls 5 gallons of water out of my cabin a day dueing certain weather conditions.

Ok, so that being said…i have had no radiators on so far, I have had my central heating off…but the boiler does vent to outside. So I will leave my heating off for the time being if that will only worsen my situation.

Does this mean the mini oil heater would not help in.the tent? And hhmmm, so I understand this a little better now, guess a good dehumidifier is my only way to go now, I will post you pic of my set up if this could help diagnose any issues?

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Ok thankyou, here are some pics, I live with neighbors either side, have problems with intale outake…currently out take as I said is blowing the hot air into the hall way outside tje grow room…so G room door must always be open too. Is this bad? I will leave the lights on until 7am the day after tomorow if thats the case…thats more than 24 hours, or do I stagger it over a couple days until I can have lights on at 7 am and off at 7pm?

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Uploading: DSC_0038.JPG… Uploading: DSC_0035.JPG… Uploading: DSC_0034.JPG… Uploading: DSC_0033.JPG… last thing, would opening up the windows to lower temp throughout the house and room work to bring temp room?

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A binch of the pics did not come through.
I can see from the one that did though that the small white fan doesnt have much clearance to affect airflow much behind it…get a bigger box fan maybe and point it inside the whole thing.
The main concern right now is humidity so…if you are dumping the exhaust back into your house and the intake is also grabbing dame air? Humidity will never decrease because you are just moving the same air around.
A window is perfect idea and will be good. Put a rh meter outside, see wjat it is. Then move it inside, see what is is. Compare to grow room. We gotta get data on the environment.

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Staggering a couple will decrease stress which is good just make sure you dont go shorter hours to accidentally flower.

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Will do tomorow in regards to out door vs indoor reading…i am unsure how to connect outake so it is blowing out of the window as it is at the front of my house on.view to neighbors. Hence why I have a blackout blind covering the open window, which currently has the intake…which is passive, no fan to suck ATM…if you have any suggestions on a stealth way to get my outake out the house would be great.