Dehumidifier Advice for 1200w grow.

[gnarly]

Hey guys, I need some advice.
Setup:
Sunhut XXL (about 4x8)
Constant exhausting airflow 24/7, which draws in air from the house or outside (if i open/close the window of the room the tent is in)
1200watts of light.

Going into flower now, we have RH around 75% in the dark and 65% in the light. This is not good. The temps are great, between 70-80. Its the humidity. Plants are in 5 gallon pots of soil.

Anyway. What size dehumidifier would you recommend for this size?

The whole room is about 8x10. I could put it inside or outside of the tent. It would be better to do outside, but no real biggie.


So... I'm thinking of getting like a 45 pint. I'm not so much concerned about the reservoir size because I can empty it daily. I'm concerned about it keeping up with the humidity in there.

Help?

 

[Rolling Bones]

In regards to the draining the reservoir, I have seen when a small 10-15gph pump was hooked up and the water was directly pumped into a feeding reservoir, so there was never any need to top off your res or emptying the thing daily.

If you do put the dehumidifier inside you room, you'll need to exhaust the hot air..othewise it'll raise your temps and thats not good...

About the size, a 45pint should be fine.

 

[gnarly]

Here's the news:
Picked up a 30pint.

It was in the growroom all night for 12 hours of lights on... And aside from raising the temps another 5 degrees or so, it didn't seem to impact the RH. I think this is because my exhaust fan runs so much air through there and the general RH from outside has been high as well.

The lights go off from 9am to 9pm. I just popped in around 8:55 and turned my exhaust fan down to about 30%. I'm hoping that while the lights are off, this dehumidifier can put down some work and draw a good amount of that moisture out. At 9pm, i'll be able to pop in and have a look at the RH, min, and max too... if it appears to work out i'll keep doing that cycle while the lights are off.

RH all night was about 65%. Thats not horrible, but still not good. I wish the humidity in this area would go let off for a goddamn minute. Its barely ever been sunny and we're in august now.

 

[gnarly]

look at this shit.
http://www.weather.com/weather/hourbyhour/95501?begHour=21&begDay=224


this is what the evenings have in store.. 90%!!! I guess the 65% it hung around at wasn't so bad, eh?

I'll just have to keep a good look out for mildew or mold. Bastard weather...

 

[caljim]

If you really want to get that humidity in check, put an a/c in that window or decide to cool that room in some way because drawing humid air through a humid room and expecting your dehumidifier to keep up just aint going to work. not to mention the $$ it takes to run that thing w/o any benefit from it.

Just a simple window unit would act to cool the air and probably dry it to the point where the dehuey would only run durring lights off.

The bennefits to be gained from a controlled environment truely outweigh the time money and effort it takes to get there.

 

[clowntown]

As you've found out, the dehumidifier isn't going to do a damned thing except use up power and create heat since the dehumidified air is simply getting sucked right out. You'll need to either create a "lung room" or similar, or think about running a (semi-)sealed setup. Such as using a separate fan for cooling the light, and less air exchanges (and/or from the "lung room") with the dehumidifier.

 

[Chaghatai]

What clowntown said. You need to defeat the fans at night and buy a dehumidifier big enough to cope with no fans running.
As for daytime, you could have 2 exhausts. One sealed exhaust cooling the lights, drwaing air from outside through ducts and sending air outside through ducts. The second exhaust exhausts the room to draw in co2 and provide cooling or dehumidification when outside is cooler or less humid respectivly. This could be set up on a timer to run for a few minutes each hour or so to provide air exchanges. Meanwhile, the dehumidifier runs to bring down humidity when the fan is off.
Having humid outside air and no CO2 supplimentation puts you on the horns of a dillema: You need to run an exhaust fan to draw in fresh CO2 from outside air. But if the outside air is humid, it becomes a high-volume humidifier.
The heat generated by the lights is lowering the humidity since you have 65%. This IMO is fine for daytime. Too dry limits the plants growth.
I've been thinking of the same kind of stuff since things are really humid here for much of the year and that season is approaching.

 

[Whatever]

But if the outside air is humid, it becomes a high-volume humidifier.
The heat generated by the lights is lowering the humidity since you have 65%. This IMO is fine for daytime. Too dry limits the plants growth.
I've been thinking of the same kind of stuff since things are really humid here for much of the year and that season is approaching.

I like to see and welcome humidity less than 20% the last 2 or so weeks of flower and don't like to see it over 55% lights on later in flower. Lights off humidity and temps are easy to control. Mold and PM issues are related more to humidity issues than 'fresh' air circulation. Humidity issues are more a problem lights off anyway.

I've had pouring down rain outside and fog yet the humidity in the room never went over 60% lights on even with an an air exchange about every 60 seconds to 2 minutes max.

 

[DIGITALHIPPY]

go get the dehumy what are you waiting for? budrot?

 

[Whatever]

go get the dehumy what are you waiting for? budrot?

Dude...he's already bought a 30 pint unit. A 50 would have been better but the 30 should serve well...as for the extra heat a small AC should counter that. No need to flow ANY air lights off...just need to control heat and humidity then...that's IT!

 

[DIGITALHIPPY]

Dude...he's already bought a 30 pint unit. A 50 would have been better but the 30 should serve well...as for the extra heat a small AC should counter that. No need to flow ANY air lights off...just need to control heat and humidity then...that's IT!

sorry i didnt see anywhere he said 'he had one' bedhumys are a great investment in growing, even if your RH seams fine. alot of plants /dwc puts off some humidity. i have a 45pinter' and its total underkill, it fills up once a day and i wish i had gotten the 65'r but it was cheap, thanks to craigslist. more people should get dehumy's.

 

[Whatever]

sorry i didnt see anywhere he said 'he had one' bedhumys are a great investment in growing, even if your RH seams fine. alot of plants /dwc puts off some humidity. i have a 45pinter' and its total underkill, it fills up once a day and i wish i had gotten the 65'r but it was cheap, thanks to craigslist. more people should get dehumy's.

I blow by so much info that people post and start typing it isn't even funny. Hard to overengineer really. I recommended a buddy install a 50 pint and in retrospect shoulda put in the 70. It was only a few bucks more and woulda served him better.

 

[G33k Speak]

As you've found out, the dehumidifier isn't going to do a damned thing except use up power and create heat since the dehumidified air is simply getting sucked right out. You'll need to either create a "lung room" or similar, or think about running a (semi-)sealed setup. Such as using a separate fan for cooling the light, and less air exchanges (and/or from the "lung room") with the dehumidifier.

I vote for AC, sealing the room and adding CO2 -screw exhaust fans - that's sooo 1988.

 

[gnarly]

thanks for the input guys. i might put my exh fan on a timer to be off during lights out and have this dehum rocking...

 

[Whatever]

thanks for the input guys. i might put my exh fan on a timer to be off during lights out and have this dehum rocking...

If you do just make sure to keep the oscillating fans going 24/7 and you still gotta make sure temps are in check. I've had many a successful grow with virtually no temp differential, maybe like 5F, between lights on and off. Humidity is the real killer here but in general the higher the heat the higher the humidity. Dropping temps will also help the humidity issue. Like I said before you may have some issues with odor but with a well sealed room, I mean like setting it up like you wanted to run closed, it will be better. Some air will still move through the ducts/fans even though they are off so make sure you monitor odor.

 

[Murphy]

Same problem for me gnarly, I was running my exhaust fan on the same timer as my light, I opend the door during light's out and I may as well have been swimming. Running the exhaust fan 24X7 helped me alot.

 

[gnarly]

Same problem for me gnarly, I was running my exhaust fan on the same timer as my light, I opend the door during light's out and I may as well have been swimming. Running the exhaust fan 24X7 helped me alot.

I did some experiments and you are definitely right. I did find a major flaw in my system. My exhaust ducting came detached from the flange on my tent, so it was sucking from the room around it, not the tent. Boy did that screw up my research/data.

Nevertheless, I've found a dehumidifier is pretty much worthless. Fans on or off, the DEHUM does nothing, or makes things worse. If i turn the fans off and run the dehum, the temps rise and the RH RISES! This is a relatively 'sealed' system, no in or out airflow and yet this thing is MAKING IT WORSE!. I remove the dehumidifier and it will stay the same... I turn on the exhaust fan (causing passive intake), and it all starts returning to better values.

If i run the dehum with the fans on or on low, it doesn't matter.. it does virtually nothing 'more'. I was able to see a 1% drop, and it might have just been circumstantial... definitely not worth the 580watts it is pulling.

When lights are on, the dehum doesn't matter anyway. Temps go to 78, RH goes to 55-60.

An AC would definitely have been a smarter choice.

 

[og dmc]

I have a portable unit that lowers the humitity by about 20 percent. There is a good and bad side though. It actually circulates and dehumidifies the air by exhausting hot humid air out a duct. Bad thing is that air is gonna be a bit stinky. I am tryong to find a way around that, but it looks like I might be getting a large window unit soon.

 

[Whatever]

Nevertheless, I've found a dehumidifier is pretty much worthless. Fans on or off, the DEHUM does nothing, or makes things worse.

Then your dehumidifier is undersized or a piece of garbage.