Do I need a dehumidifier if so how big?

Hi all,

First time with an indoor setup and into week 4 of flowering now, things are looking good.

The weather has recently got a bit warmer and wetter (as is traditional in the northern hemisphere at this time of year), outdoor humidity is around 80% at the moment.

I'm finding all the fun that comes with even a few degrees of additional ambient temperature and HPS, but with the exhaust on constantly it's all good.

I get the big impression that humidity is bad for this late stage as we want to avoid any rot, mould etc, along with spider mites and other potential nightmares.

Is it a good idea to get a dehumidifier?

It would seem logical to assume this would be a good idea, however how big?!

Currently going through 6 litres of water / day in the tent (1L / plant), and from what I've read it seems like the majority of this is transpired by the plant. Therefore to maintain a status quo if the tent was sealed with no air leaving - we would require a dehumidifier that removes 6L a day - am I right?

Obviously however a large portion of this water must surely be removed through the continuously running exhaust fan.

Space is currently a bit limited, so putting something large in there isn't an option. I was hoping to get a 500ml machine - but maybe this is just too small and not worth it?

space: 1.2m x 1.2m x 2m
medium: coco

What are your thoughts? Thanks for your advice.

"Go big or go home" Bigger is always better and doesn't have to work as hard. If it's hot and humid you need AC. Dehumidifiers will make some heat which is bad for the terpenes.

70's natureboy said:

"Go big or go home" Bigger is always better and doesn't have to work as hard.

Click to expand...

This is often my mantra however I've defo no space or budget for AC at present, and a big factor is stealth.

Really good point about the heat generated.

Ambient daytime temps (lights off) are still under 20, and shouldn't climb more than a few degrees before harvest.

Nighttime temps (lights on) are between 2 and 10, so with my lights and fans its about manageable.

Light wise I'm running (both HPS) 1x 600W and added in a 250W that someone didn't need to offer some more light coverage.

I can switch the 250W for a 300W flowering LED (specific details of this light are totally unknown - other that it came from china preassembled) if things start getting too hot. I figure from some of the posts here on RIO that things progress much better with slightly less light and the right temperature instead of more light and a bit too much heat.

you venting your exhaust out a window or recycling it within your home?

if you're recycling the air you could just put a dehumidifier in the room that the tent is in and it will solve your problem.

but snce your HPS in a warm climate, i'd bet you're venting outside, you'll probably need thermostats and timers for your exhaust fans so they're not just constantly getting rid of all your dehumidified air. putting a dehuey and then having 24/7 exhaust isnt gonna do anything. you'll get a thermostat for your dehuey so it kicks on when RH reaches a certain % and theromostats for your exhaust so it only kicks on when temp reaches a certain point. will take some dialing in.

in addition to all this a powerful oscillating fan inside your tent will fight mold and high RH (probably at the expense of a little yield)

honestly, if i lived in a place with 80% RH, the #1 thing is getting a strain that is meant for high humidity and extremely mold resistant.

you're gonna have to do something. if you have 80%RH and nightime temps around 70deg YOU WILL GET ROT.

olafthegreen said:

Hi all,

First time with an indoor setup and into week 4 of flowering now, things are looking good.

The weather has recently got a bit warmer and wetter (as is traditional in the northern hemisphere at this time of year), outdoor humidity is around 80% at the moment.

I'm finding all the fun that comes with even a few degrees of additional ambient temperature and HPS, but with the exhaust on constantly it's all good.

I get the big impression that humidity is bad for this late stage as we want to avoid any rot, mould etc, along with spider mites and other potential nightmares.

Is it a good idea to get a dehumidifier?

It would seem logical to assume this would be a good idea, however how big?!

Currently going through 6 litres of water / day in the tent (1L / plant), and from what I've read it seems like the majority of this is transpired by the plant. Therefore to maintain a status quo if the tent was sealed with no air leaving - we would require a dehumidifier that removes 6L a day - am I right?

Obviously however a large portion of this water must surely be removed through the continuously running exhaust fan.

Space is currently a bit limited, so putting something large in there isn't an option. I was hoping to get a 500ml machine - but maybe this is just too small and not worth it?

space: 1.2m x 1.2m x 2m
medium: coco

What are your thoughts? Thanks for your advice.

Click to expand...

You have to dehumidify the area the tent is in.
Leave your flaps open as much as possible, use fans, and buy a dehumidifier for the entire area, not just the tent.

Thanks for your help and common sense guys, adding a dehumidifier in the area the tent is contained within is a possibility, as its a garage. I wasn't keen on having a big noisy tent in there, but just having a dehumidifier loose in the garage is not at all uncommon.

I'm not having an issue with moisture or anything within the tent it's always dry even when the lights come on in the evening. I suspect this is due in part to them needing slightly more water than they get. I could probably have watered them after 12h as after 24h they are bone dry - but not wilting. So there probably isn't much transpiration going on in their night time (our day). the 16L pots are better than the 12L ones I got at first.

Currently I'm just sending exhaust air into the same space as it's like 5m + high (pitched) and a bit ventilated anyway.

There's nothing consistent about the weather here at this time of year which is the big issue. If it gets hot it can get humid and stormy, it can also stay hot and dry, or it can be cold and wet. Damn unpredictable beautiful mountains. But as a general rule we get sun 80% of the time. Im not in the tropics

The upcoming forecast is for RH of around 50% with lots of sun. It's been raining for the past few days which is not that common.

So overall it sounds like a need a more powerful machine for the whole space, for wet periods. I've potentially found one to borrow for a month, will find out tomorrow.

Fuck if it aint broke then who needs a dehumid. If air moves it shouldnt cause moisture build up so assume exhaust takes care of that or they be mold already.

Id wait till disaster strikes first but others may wanna try pre empt everything

I live in the Smokies(as in foggy) so humidity is ALWAYS high. I finally broke down and bought a de-huey last winter and it made a significant difference. You will have to be able to mitigate the additional heat so if that's a no-go then a/c is the best option. I use a 50 pt in my 5x10x8 area and she does a great job.

You can use this stuff, but have to monitor humidity manually. It can over dry small tents! They are simple but help... good luck!

https://www.rollitup.org/t/home-made-dehumidifier.135433/
https://byemould.com/2017/09/04/homemade-dehumidifier/

2. The Calcium Chloride Dehumidifier

Hang calcium chloride in a sock to keep humidity levels down
You may have heard about the rock salt dehumidifier but have you heard about the calcium chloride dehumidifier?

The calcium chloride moisture absorber is even easier to make than the rock salt dehumidifier.

You will need

• String
• A sock or lycra stocking
• A medium / large bowl or container
• Calcium Chloride (you can buy on Amazon here)

Method

• Place the calcium chloride inside the sock or stocking and tie a knot at the open end of the sock
• Tie the string around the knot of the sock and hang the sock somewhere suitable
• Place the bowl underneath the sock or stocking to collect the resultant water.

Make sure that the bowl is large enough as over time the calcium chloride will turn into liquid. Replace the calcium chloride as required

mannurse801 said:

You can use this stuff, but have to monitor humidity manually. It can over dry small tents! They are simple but help... good luck!

Click to expand...

Thanks, looks interesting and totally silent to boot, apart from some occasional dripping.

Still waiting for the machine, but it's been really warm and dry here, so humidity has been around 50. It's meant to be ok for a few more days.

I got a big dehumidifier, with it set to 35% outside the tent it gets to about 60% rH in the tent.

Is this going to be ok throughout flowering - so far I cant see any traces of mould, or should I look at some way of getting it into the tent?

I think it would be pretty effective even with the exhaust running constantly, but it's extra heat I really don't need in there when lights are on. It's pretty crammed in there anyway...



Lights off temps seem to be around 18C (65F) in there, lights on - between 28C (82F) & 23C (73F) depending on outside temps. rH seems stable at ~60%

Thanks for your help

You may get away with 60 RH in flower but it's borderline IMO. Make sure you have good airflow will help and I would defoliate to thin out the leaves and reduce chance of WPM and mold. I know that some growers do not agree with defoliating but it can help keep your buds safe when you borderline RH.
If you go with a DH, you can run it in the Garage and use a 4" duct to run some of the warm dehumidified air into a tent port. Problem there is you will probably need AC to make up for the heat your DH sends into the tent.

You'll get away with 60. Actually, my tent is always 55-75 depending on the day and time of year. I've never had mold issues during flower. There was a thread here not long ago with the debate about flowering at 30%rh vs. 60% rh. 60%rh won't cause rot. But you can still get rot at 30%rh if you have big swings.

And that's what's key imo. Less humidity swings. And airflow

SheeshM said:

I would defoliate to thin out the leaves and reduce chance of WPM and mold

Click to expand...

I've been considering defoliating, I've taken a few lower and yellow leaves, but I've not had the heart to attack higher up. There's a few fan leaves I could imagine removing, but otherwise I need persuading! I've read so many debates on here and other forums about defoliating, it just sends you crazy.

T macc said:

And that's what's key imo. Less humidity swings. And airflow

Click to expand...

I've got another fan I'm going to get in there, and I'm going to make a basic hood from a cardboard box and some 5" ducting I have to see if I can get some more dry air in there - just to be safe.

Thanks for your continued help and advice.

70's natureboy said:

"Go big or go home" Bigger is always better and doesn't have to work as hard. If it's hot and humid you need AC. Dehumidifiers will make some heat which is bad for the terpenes.

Click to expand...

That is not accurate.

De-humidification is, quite literally, air conditioning. Bigger is NOT always better.

For a space that small, a big huge dehumidifier would heat the tent up too much and also run for a very short period of time. Then of course the humidity would have to build up to the point it engages again.

So what you wind up with using a big, huge dehumidifier is a yo-yoing dry as a bone, wet as a dish towel environment.

You're only dehumidifying a very small space, get one that best fits the area. It will run longer while producing a lower, more even flow of heat and make the environment far more stable for longer periods of time.

Since we're only talking about roughly 130 square feet of space, this little bugger would do the job quite nicely: https://www.amazon.com/Dehumidifier-Electric-Ultra-Quiet-Auto-Off-Basement/dp/B0751CRWYR/ref=asc_df_B0751CRWYR/?tag=hyprod-20&linkCode=df0&hvadid=222951636391&hvpos=1o1&hvnetw=g&hvrand=10858852440984454378&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9011015&hvtargid=pla-365208491490&psc=1

You'll just have to stay on top of keeping it emptied. Check it at least twice per day.

Well things are looking a bit curly and dry in there now!

I've had the dehumidifier blowing into the tent. Humidity at the bottom where it was 18 degrees was a constant 60-65%. However around the lights where it was much warmer - humidity is only 30%. I tested this morning for the first time at the level of the top bud when I noticed some of the leaves look slightly curled.

I've moved the DH so it's not blowing directly into the tent air intake, hopefully they will recover!!