Tips and tricks for dealing with high humidity? Looking for someone with experience

[FlooK]

Been growing for around 5 years and trying to bring the quality up a level. The largest improvement I can make imo is solving the humidity problem.

 

Currently sits around 70-80% RH during lights out. 4x4 tent sits in lounge which stays roughly 20c. 

60-70% RH during lights on. Temp 27c or so. 

 

Growing in coco and only watering once per day at the moment. Once i've fixed the humidity i'd like to increase it to 2 or 3.

 

Firstly how are these numbers? I believe they are a little on the high side from what i've seen / read. VPD etc. I've also had issues in the past with mould, nothing horrendous but lost 1 or 2 colas because of it. 

 

The ventilation setup uses a 6" AC Infinity extraction which pulls air from the lung room (lounge) into the tent, then it gets forced down a 6" line and out of the chimney. 

 

 

I've noticed the outdoor air is obviously a lot colder and holds less moisture, would it be worthwhile running duct to a near window so I can pull air from outside? My only concern then would be the tent temps would drop a lot, maybe not so much of an issue during lights on but when the lights are off I could imagine it dropping fairly low. Would this be a worthwhile trade off? Would it even solve the higher humidity?

 

I've also recently bought a dehumidifier but they're a fortune to run, not an issue at all leaving it on during final weeks of flower / drying but i'd rather avoid running it none stop during the 8w of flower. 

 

There's tons of knowledgeable folks here hopefully someone has solved a similar issue

 

Thanks for having a look. Please let me know if i've missed anything out. 

 

 

 

[stu914]

High humidity is ok for the first few weeks of flower, once the buds are set it needs to be lowered.

I left my latest crop 60 - 70% humidity for too long this time and suffered some mould, I cut that out and

installed a dehumidifier which dropped the humidity below 50%, increased air circulation and extraction,

cropped last week with no more mould.

It's a trade off regarding a dehumidifier, either intstall and cut out mould or not and suffer losses.

Might be worth checking the humidity at the intake to see if it's contributing to the high readings.

Hope you get it sorted bud...

 

[sweettooth]

What lights you running? I only ask as once I redirected the output from an air cooled hood and had that as an intake which was drying and warming the air, that helped.

 

Do you have standing water in pots or trays - that will raise RH.

 

How are you running the dehumidifer? The best and most effieicnt way is to duct it so the dry, heated output is acting like your tent intake, having it inside is just wasteful. a 12L unit would keep a tent that size happy and only pull 220 watts. Dehumidifier aside, the only way is to get a bigger fan and pull more air but if your houses RH is on the high side, youre only option is the dehumidifer.

[mikeydoughnut]

You need a dehumidifier. There’s no other way around it I find. You’re playing a lottery without. My kitchen alone without any extra input from transpiring plants or boiling keckles was 71% this morning. I just put mine on from week 5/6 depending how things are looking otherwise I’d never ever be below 60. I hook it up to the intake. It costs a good few quid like but so does lighting and heating rotten weed. Also keeps the whole upstairs dry during the cold months. No condensation or owt. Other than that. Create a hurricane and Hope nowt gets poorly. 
 

e2a - try and keep steady temps too. Too dramatic a drop at lights off can create moisture/dew. A govee or any other environment ‘tracker’ can help since they display all activity from when you switch it on. Dew point is a handy function. I wouldn’t rely on it as a baseline for temps to run but its reassuring when yer sat 12 degrees away from dew point. It’s my lickle rot comfort blanket …

Edited October 9, 2023 by mikeydoughnut

[FlooK]

Thanks for the info fellas. Definitely agree with needing a dehumidifier. My lung room sits around 70%RH or so, throw in transpiring plants etc and its no wonder the tent is at 80% give or take. 

 

@sweettooth

Im running a Meijiu 750w LED board and nah i use a drainage tray and a condensate pump so all the waste water is removed, spent a lot of time setting this up and it did fuck all to alter the humidity which was a bit disappointing! 

The dehu I run is this model: 

Sadly there is no way to attach the intake to it but I might try macgyver it and bang a ton of tape on so it’s air tight. 

 

@mikeydoughnut

Quote

It costs a good few quid like but so does lighting and heating rotten weed

 

very true!! my lights off temps don't fluctuate too much in fairness. roughly 20c during the day when lights are off and 26, 27c or so when the lights are on at night time. 

Edited October 9, 2023 by lildaveham
Please don’t post Amazon links.

[GSZZ]

54 minutes ago, FlooK said:

roughly 20c during the day when lights are off and 26, 27c or so when the lights are on at night time. 

 

Based on what you've posted your dew point is 21c, and your lights off temps are 20c - so you're hitting dew point, its no wonder you are getting bud rot. If you used a dehumidifier to reduce the RH to 50%, your dew point becomes about 16c, if you just reduce to 60% your dew point becomes 18c.... Or you could heat your night time temps above the dew point and achieve the same result without having to reduce humidity at all.

Edited October 9, 2023 by GSZZ

[stu914]

14 minutes ago, GSZZ said:

dew point

 

This something I've never fully understood, I've always tried to get the difference in lights on/off temps as small as possible.

In all my years I've only had mould about three or four times and never really put humidity down as the cause.

You know sometimes when your brain really really hurts...

 

[GSZZ]

@stu914 Temperature acts like a container for moisture in the air, the higher the temps the more moisture it can hold and vice versa. So as the lights go out and temps start to cool rapidly, for every 1c that drops the humidity goes up by however many %, because the the container of air is getting smaller - thats why its called relative humidity. Imagine dew point being the point where the moisture spills out of the container because it can't hold anymore.

[stu914]

@GSZZ

 

OK that makes sense (to this poor old addled brain) so how do you work out the overflow point?

Is there a set chart which says if humidity is X temps are Y then dew point is...?

 

[sweettooth]

@stu914 dpcalc.org is great for working out your dew poiint. i have my dehumidfer ramp up 30 mins before lights off to bring RH right down so my dew point isnt as high

[sweettooth]

whast inteseting as a test and example is if I run my room at 32 degrees and 70RH, my temps only need to drop to 25 and im at dew point so need to either add more heat or raise the RH and dont let the temps drop that sudden

[The Villan]

3 hours ago, stu914 said:

@GSZZ

 

OK that makes sense (to this poor old addled brain) so how do you work out the overflow point?

Is there a set chart which says if humidity is X temps are Y then dew point is...?

 

 I only recently looked at dew point and thats because the govee hygrometer I bought gives just that, temps, humidity and dewpoint it even gives VPD, although I am not sure onn the readings exactly, it was mentioned in another thread somewhere that if vpd on the graph is around .75 to 1.2 the room is within RH conditions to avoid mould. Please correct me someone if I have understood this incorrectly.

Edited October 9, 2023 by The Villan

[ratdog]

as has been mentioned, keep temp differences to a minimum and things should be fine, i aim for a difference of 3 degrees, no more than 4 max, that's a light's off with a min of 23.5

[Military Grade]

Another one for a dehumidifier and lowering the swing in Lights on and off temps

 

Tube heaters are great for some use cases like mine.

[Moonstone420]

10 hours ago, sweettooth said:

What lights you running? I only ask as once I redirected the output from an air cooled hood and had that as an intake which was drying and warming the air, that helped.

 

Do you have standing water in pots or trays - that will raise RH.

 

How are you running the dehumidifer? The best and most effieicnt way is to duct it so the dry, heated output is acting like your tent intake, having it inside is just wasteful. a 12L unit would keep a tent that size happy and only pull 220 watts. Dehumidifier aside, the only way is to get a bigger fan and pull more air but if your houses RH is on the high side, youre only option is the dehumidifer.

 

 

Hi mate.

 

Could you elaborate on this please. Just trying to get a better picture of what you mean by this setup method.

 

Are you saying get an intake fan to suck the dryer air into the tent, or to leave the dehumidifier near an intake flap. For what its worth I only run passive intake myself. 

 

As we speak i am trying to sort buy one myself, but really dont want it in the tent, so your method may help. 

 

Thanks

 

 

 

 

Edited October 9, 2023 by Moonstone420