Air Ciculation, Temperature, & Humidity

[Herborizer]

Hello. I am trying to solve a low humidity problem and I am hoping I can get some feedback/advice so that I can dial in my grows.

I have been growing for about a year. I have had some good success and a ton of learning along the way. In my battles of fighting with powdery mildew, along the way I have equipped both my mother/veg room and my flower room with constant running (24x7) Ellicent vortex exhaust fans. So each room has negative pressure, pulling in air from outside through vents, and exhausting outside via the Ellicents.

One of the side effects of running these exhaust fans 24x7, I noticed that my temperatures stay pretty low (and constant) while lights are on. Also, temps are pretty low (low 60's) at night during the winter (summer isn't a problem). Though I am not sure the temp thing where I live is that big of an issue, since I am in the 74-82F when lights are on, and 62-74F lights off year around. What I am more worried about is the RH (relative humidity).

Basically, I am running about 27-38% RH in both of my rooms year around. In other parts of my house I am about 45-54% RH. I attribute the low RH in my grow rooms to the exhaust fans.

My mother/veg room is is 5 feet wide, 3 feet deep, and 6.5 feet tall. I am running a 4inch Ellicent (running 24x7).

My flower room is 5x5 feet by 6 feet tall. I am running a 6inch Ellicent in there (24x7).

I have considered a humidifier, but with those fans running, I believe it just gets sucked out almost immediately. I have thought of putting my exhaust fans on timers, but I am worried that I will get a lack of CO2 (stagnant air) issues.

Anyone battle with this type of problem? Any advice you can throw my way would be greatly appreciated.

Thanks!

 

[stagehand099]

C.A.P. makes a temp/humidity controller that would turn your fans on at a setpoint of your choosing and would exhaust until the temp/humidity reaches a point below your setpoint. So, instead of a timer, you could control the perameters of those varibles within an ideal envelope. $120.00 + shipping. Might find it or something like it cheaper if you look around the net. Ciao!


http://www.plantlightinghydroponics.com/cap-air1-temperature-humidity-control-p-361.html

stagehand

 

[Guest 18340]

Curious as to what issues you're having with RH that low?

 

[Herborizer]

Curious as to what issues you're having with RH that low?

At times the edges of the leaves are cupping. Very low RH is known to decrease yield as well. Another issue, is rooting clones is difficult in such low humidity (of course a dome works).

 

[Herborizer]

C.A.P. makes a temp/humidity controller that would turn your fans on at a setpoint of your choosing and would exhaust until the temp/humidity reaches a point below your setpoint. So, instead of a timer, you could control the perameters of those varibles within an ideal envelope. $120.00 + shipping. Might find it or something like it cheaper if you look around the net. Ciao!


http://www.plantlightinghydroponics.com/cap-air1-temperature-humidity-control-p-361.html

stagehand

Thank you. This is a very nice addon for sure.

My concern though, is if the exhaust fan isn't running all the time (and since I am not running supplemental CO2), wouldn't the lack of air flow cause issues (due to lack of CO2)? In all the hydro books I have read, they speak of hose CO2 is completely depleted around a plant in as little as 5 minutes.

Thoughts?

 

[SecretGardener]

Thank you. This is a very nice addon for sure.

My concern though, is if the exhaust fan isn't running all the time (and since I am not running supplemental CO2), wouldn't the lack of air flow cause issues (due to lack of CO2)? In all the hydro books I have read, they speak of hose CO2 is completely depleted around a plant in as little as 5 minutes.

Thoughts?

I am struggling with the same issue. Here are a few idea's I am considering that may help you as well:

a) make the size of the intake vent hole a little bigger then the exhaust.
b) buy a timer with 15 minute timing intervals. that way you can turn the fan on for 15 mins and off for 15 mins - or however long it takes for the RH to rise too high in your tent.
c) seal your tent completely and suppliment CO2

 

[faulker]

you want low humidity in flowering, your rh level in your flowering room is good, i wouldnt change anything there. veg room is where you want higher humidity. what lights are you using? i wouldnt exhaust that room, use your vortex to just circulate the air in there, that alone will bring your rh up. if u need it even higher get a small cool mist humidifier

 

[dunkydunk]

I don't know if there is any scientific reasoning behind this, but I've noticed my digital hygrometer gives a lower reading than my analog hygrometer in a room of negative pressure.

 

[FlaDankster]

Went from a 170 cfm fan to a 449....

RH went from 45-50 down to 35-40....

Added 2 2 liter bottles of water with a small airstone and air pump and RH is up to 43-47.Thats good enough for me.Don't take up no room at all.I do turn off the air pump at lights off though...even though i haven't checked my lights off RH.

I have 2 strains in there and one did just as you describe with the leaves while the other isn't bothered by it.You can feel the difference in the leaves also,they feel some what papery i guess is how i wanna say it.Yield stills looks the same though.

FD

 

[odium33]

turn your exhaust fan off a couple times a day? heat = more humidity. most people here would kill to have this problem lol!

 

[Chief Rbud]

i wouldnt worry about a high tech fix for your low humidity, i would just foliar feed the vegging girls with mollasses and water 3-5 times a day at a rate of between 1 tsp to 1 table spoon / gallon of water. get a new spray bottle from walmart, they sell empty ones, and mix the water/mollasses in a gallon jug and mist the vegging girls several times a day until the humidity is where you want it, i even do this in flowering as long as the fan is moving enough air and i dont already have high humidity. works great! , i wouldnt do this in flowering with rock hard dense indica buds, i grow sativa dominant hybrids.

 

[Work2much]

Herb any progress with low RH?

Other parts of your house average around 50% so I would assume that outside would be the same so I think a larger air intake that would exchange the air/RH more frequently in your veg/flower rooms would raise your RH up closer to what it is outside.

I'm having exactly the same problem btw and found this post on a search for "humidifier". My RH over 24 hours is going from low teens to mid thirties so its even worse then yours and the leaves are showing it too. A small $40 cool mist humidifier did absolutley nothing so you were right in your assumption that the exhaust would suck all the humidity out.

 

[Herborizer]

I have sort of given up on this for now. I tried putting a timer on my exhaust fan, and this worked. Though, when the humidity would change outside (big swings because of weather), I had huge swings inside too. Very frustrating.

I also tried putting a fan speed controller. This worked, only if I put the speed on it's lowest setting. This was the most stable of everything I tried. Though, i felt there was a lack of air circulation and my plants started suffering. So I scratched that.

I tried a humidifier, and this did work to an extent, but it's either too high humidity or too low and the water runs out all the time.

So now I have decided to just live with my low RH and learn to adapt my plants to this. Best I can do for now.

 

[Work2much]

I have sort of given up on this for now. I tried putting a timer on my exhaust fan, and this worked. Though, when the humidity would change outside (big swings because of weather), I had huge swings inside too. Very frustrating.

I also tried putting a fan speed controller. This worked, only if I put the speed on it's lowest setting. This was the most stable of everything I tried. Though, i felt there was a lack of air circulation and my plants started suffering. So I scratched that.

I tried a humidifier, and this did work to an extent, but it's either too high humidity or too low and the water runs out all the time.

So now I have decided to just live with my low RH and learn to adapt my plants to this. Best I can do for now.

Thank you for the quick reply.

The humidifier you used, what type/size was it? I'm thinking about buying a large $300ish one to overpower the exhaust as I mentioned above the little $40 one did nothing. I'm not ready to close the room up and run co2 just yet but I do feel my plants are suffering from the super low RH so I feel I've got little choice but to buy the big one. My C99's laugh at the low RH, but my SSSDH don't like it on bit.