High Humidity At Night - DIY (Do It Yourself) Solution?

My flower tent got up to 99% RH last night and I'm getting scared. I have an AC unit that keeps things in line while the lights are on (45-55%), but at night I have to turn it down so it doesn't get to like 58 degrees. I realize my ventilation, or lack-thereof, is mainly the culprit, but my extraction fan can't push as much air through my carbon scrubber as I'd like it to and there's nothing I can do about it right now.

So, in the meantime:

- Should I make my own dehumidifier out of a thermoelectric cooler? (TEC dehumidifiers get awful reviews, it's the only reason I'd build it myself)

- Should I just buy one of those "renewable" dehumidifiers (or make my own) and save up for a better extraction fan?

- Should I keep my AC turned up and let the tent get cold at night while I save up for a better extraction fan?

- Should I do something else?

I have a feeling I won't be able to buy a new extraction fan until after I harvest this plant, so whatever the solution is it will have to be able to finish this girl off. Thanks for any and all input guys.

Can you leave the flaps open at night? If you can that could be the answer, if you can't, the AC running at 70-75 degrees all the time is another option until you can change your fan. They also make bags of desiccants used for damp basements. They might have them in your local hardware store, and they are on line. Those will definitely help. Good luck.

I was leaving the flaps open (passive intake) before I got the AC unit (active intake) and I don't remember RH getting nearly this high. You have a point. By adding the AC, though, I moved some things around so now light leaks in the flower tent would be an issue with open flaps (nighttime for flower tent is not actually nighttime). I'll have to either suss that out, I guess, or get one of those renewable dehumidifiers like you mentioned until I can upgrade my fan.

Thanks for the input.

Left the flaps open and it wasn't too much help. Still got up to 95% past few nights.

I'll have to assess how much disposable income I have in the near future and decide if I'll just get some Damp Rid, by a small ~20 pint dehumidifier, and/or get an S&P TD-100 inline fan.

Thanks again, Jimdamick.

Just throw rice all over the place

u could make leave the AC on and turn it up heat wise.. until u find the sweet spot were it keeps ur room warm /cool enough.. and ur humidity down.. I had this problem also. if u can . add more fans to move the air around.. and do some research on DEW POINT.. it mite help u understand whats going on .

letstry said:

Just throw rice all over the place

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Nice one,I will try that one.
regards
sold

Can you leave the flaps open at night? If you can that could be the answer,

yjetyietijian said:

Can you leave the flaps open at night? If you can that could be the answer,

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I tried with the flaps open for I think three days. One day it decreased the RH by a few percent, the next day it was still at 99%. I built a new carbon scrubber and it has a lot more air flow. One night it got down to 92%, but that was still with the AC on pretty high. If I put the AC at a medium setting it's still 99%.

I think if I got a new extraction fan it would help/eliminate the problem, but the S&P TD100 that I'm looking at is like $75-$80 and I don't have that right now. I need to either get one of those "renewable" dehumidifiers or make my own with some Calcium Chloride. Those are my cheapest options, atm.

http://www.ebay.com/itm/Bionaire-BDQ01-UC-Mini-Dehumidifier-/350823054903?pt=LH_DefaultDomain_0&hash=item51aeaefe37
That also seems like a less viable option. $34 is more than I wanna spend on a "quick fix," especially one with questionable results.

-edit-
Or I can leave my AC on max, turn my tower fan's heater function to medium and waste more energy, yet lower the RH by raising the temperature. (Thanks K.O.) Not sure if I wanna do that, though. I don't have the documentation on that thing anymore, either, so I have no idea how many Watts that thing draws. Not sure if it's worth it. I also skimped on the ducting coming off the AC unit, it isn't insulated, so if I leave the AC on max I'm positive I'll get condensation on the ducting and I don't want it dripping where it would be dripping. Wow. This is too complicated.

holy fuck! 90+ % is a disaster waiting to happen. Hell, it's probably already started and you just haven't noticed yet.

Better put a couple of oscillating fans in there to move that air around at least.

Dehumidifier, dehumidifier, dehumidifier.

What size/cfm extraction fan are you using? I am using 4 'PC' fans in line of my 6" ducting (had to cut the corners off the fans to make them fit). They push 155cfm ea @ 12v but are a little noisy at that power so I tone them down by putting them at 9v and they still seem to push 100-125cfm ea. If feels like a leaf blower coming out the vent on the outside of the house.

Not sure where to buy single fans though.. I have a huge supply of old Dell computers I scavenge from.
http://www.aliexpress.com/item/FOXCONN-12038-PV123812P2BF-12V-1-3A-For-Dell-Dell-Optiplex-960-cooling-Fan/456821916.html

CaliJoe: I have to push the air through my carbon scrubber, I can't use PC fans. I've got a Panasonic Whisperceiling rated for 80cfm and it's having an issue pushing through the filter, although my new design has increased flow dramatically.

joe macclennan: The thing is -and I'm sure you know- is that I basically already have a dehumidifier... the AC unit. Even running at max with temps in the 55 degree Fahrenheit range the RH is still above 90%. During lights on it's around 45-55% so I'm fine there. What K.O. was saying is that because I'm removing humidity with my AC unit I'm simultaneously decreasing the temperature of the room which decreases the air's ability to hold moisture. So, while there is less moisture in the air it's still a very high RH number because the air can physically hold less moisture. If I was to use my tower fan to warm the air to counteract the AC's cooling effect the RH number should drop dramatically because I'm still removing the moisture yet the temperature isn't as low. I have a feeling as soon as the AC unit were to turn off, however, I'd cook my plants. I'd have to see how warm that thing gets on it's lowest setting. I think it just has High, Medium, and Fan. I've been using the fan and swing options to circulate air underneath the canopy.

And as I'm sure most of you know, a dehumidifier is just a glorified window AC unit that blows both cold and warm air (effectively not changing the temperature at all) off both their coils while collecting the condensed water off the evaporator coil. They are expensive and large and I don't have the room or money. I could opt for a thermoelectric dehumidifier, but their effectiveness is questionable, as is their reliability.

So, I've purchased three pounds of Calcium Chloride off eBay. I will be making a DampRid clone with the stuff. I'll report back with pictures and the effectiveness of the unit.

Wish me luck.

Have fun, all, and stay safe.

okie dokie then. I am hvac by trade so yes I know how these things work.

As stated previously. Get a dehumidifier or you will most likely regret it.

Damp rid DID NOT WORK for me. I still have a humidity problem. Avg 60-65% (not nearly as bad as yours). Just whatever you do, you wabt to keep the air in your tent moving as much as possible. Good luck, but I feel a duhumidifier is your only option. I am waiting for the warmer temps to comedown in my area, as dehumidifiers will be going on clarence soon.

joe macclennan said:

okie dokie then. I am hvac by trade so yes I know how these things work.

As stated previously. Get a dehumidifier or you will most likely regret it.

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Cool. I've been helping a few HVAC guys in my area do furnace installs recently (thinking about getting licensed). Off one of the furnaces we pulled I got a draft inducer blower as scrap. Do you think if I clean that thing up it can push more air past my carbon filter than an 80cfm bathroom fan? I'm currently using a Panasonic FV-08VQ5 for extraction and while my new carbon filter has bumped 99% RH down to 90% I'm still in rather troubled waters.

I got the Calcium Chloride in the mail and built the DampRid clone (it's in the tent now) so in a few days, at the very least, I'll report back with an update on how it went, but if it's successful I'll post a few pics to show inquiring minds exactly what I did. Total cost of the DampRid clone was ~$13 and easy as hell to make. If I think it works well enough I might add a PC fan to increase the amount of air the thing sees.

Wish me luck, and thanks again for all the help, guys.

only 80 cfm, dayum. I run 350cfm in, and 782 cfm out my massive carbon scrubber, plus my a/c in a 4x4x6.5 tent. these are real fans, not boosters. since you have a/c (didn't read if it were a portable unit or not), but if portable, most units have a dehumidifier function. after the 12hrs os over, remove the exhaust line and switch to dehumidifier mode. problem solved. ive used damp rid in the past for water leak issues and its worked perfectly. good luck OP and get those r/h% down FAST!!!!

Thanks, DemonTrich. I'm running LED if you weren't aware, so I don't need as many cfm's, I'm just circulating the air. Also, I wanted my grow to be as silent as possible, hence the WhisperCeiling fan, but no AC in my room (80+ degree temps in bedroom) plus the heat off the LED's lead to me having to convert a window AC to exhaust into my attic and ruin any hopes of a truly stealth grow. Also, since it's a window AC I can't easily convert it to a dehumidifier and back everyday.

I checked my room and RH is ~50-55% which is higher than I thought. That means RH is actually lower in my flower tent half of the time.

Good news, though, the Calcium Chloride flakes were sweating almost immediately. RH isn't much lower right now than it was before, but I'll wait to see what it does after 24 hours with the AC off. If it shows promise perhaps I can tweak the design, or simply add another to increase the effect.

just get some damp rid or put a small dehumidifier in the tent.

No the draft inducer motor you took from that furnace is less then capable at best is would be rated at about 60 cfm ,but more likely in the 40 t0 50 cfm range ,

you have tried many things to control your humidity ,it seems like you might want to think about moving your location if you cant get the humidity under control with all you have done .

I would be concerned about the calcium chloride you are using , Im not sure but I would have concerns about the gases it may release effects on your grow, that is some pretty powerful stuff, I would say you would have the same results with cat litter or speedy dry .

you might want to rethink your apporch on using a A/c unit as a dehumidifier , you are certainly correct the 2 systems do act Alike ,but you have to understand the specifics of removing Humidity , you see its the rate of air flow that you are moving across the dehumidifier coil , the air moves at a much slower rate ,therefore extracting the max amount of moisture from the air. (when sized properly) this is why Joe Mc posted about getting a DEHumidifier you have to understand the principle Physics of Air (science)

A A/C system moves air across the coil at a much faster rate ,therefore not being as efficient as a Dehumidifier ,and if the said A/C system is over sized for the said sq ft the moisture removed is at even a much lesser rate . therefore you might only be removing a very small amount of moisture in the air. hope this helps a little good luck.

The window AC dumps condensation into a Rubbermaid roughneck tote. No idea how many gallons the roughneck is, but it's quite a bit (37gal?) and it fills up at least once every week if left on during lights off. The AC unit is removing quite a bit of moisture, but obviously not enough, especially in comparison to the temperature drop it creates. And perhaps the amount of moisture it traps has to do with the relatively high RH in the room to begin with.

Thanks on the heads up with the draft inducer.

I can't move my tents. If the CaCl2 doesn't fix the problem I have to save up for a dehumidifier that can handle the entire room (not just the closet).