Humidity Question

Deathhasnofriends

Deathhasnofriends

Member
Just curious how low my humidity can be in my flower room I'm running 2 1000 watt air cooled hoods exhausted by a 6" inline fan with a carbon filter. The fan is set on low also 6" inline intake fan also set on low pulling in fresh air through a hepa filter. With a 16" oscillating fan my temps hi is 81℉ and low is 66℉ humidity high 53% RH humidity low 27% RH when the lights go out the humidity climbs when my exhaust fan kicks on it sucks the humidity right out even on the lowest setting. Here is a picture of my tent setup.
 

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tropicalcannabispatient

tropicalcannabispatient

Well-Known Member
Deathhasnofriends said:
Just curious how low my humidity can be in my flower room I'm running 2 1000 watt air cooled hoods exhausted by a 6" inline fan with a carbon filter. The fan is set on low also 6" inline intake fan also set on low pulling in fresh air through a hepa filter. With a 16" oscillating fan my temps hi is 81℉ and low is 66℉ humidity high 53% RH humidity low 27% RH when the lights go out the humidity climbs when my exhaust fan kicks on it sucks the humidity right out even on the lowest setting. Here is a picture of my tent setup.
Click to expand...
Too much fluctuations between day/night rt/rh.
 
Deathhasnofriends

Deathhasnofriends

Member
So how exactly do you guys control humidity I can't afford a big humidifier because and I have a cool mist ultrasonic rated for a 20 x 20 room and when I put it in there again the exhaust fan sucks the humidity right out of my tent. Set it to run at 70% humidity the max for this model and no change in the rooms RH also I have 2 5gallon buckets filled with water and a towel to help the wicking effect I'm at a loss on how to get stable humidity.
 
Deathhasnofriends

Deathhasnofriends

Member
Or can I just keep my carbon filter and fan running 24/7 and keep the room at about 25 to 28% humidity is that okay for flower? Cuz I wasn't sure if that was too low.
 
S

Six9

Well-Known Member
Nice setup OP, sounds like keeping intake and exhaust running 24/7 will do the trick, 25-28 % humidity in flower is nice. Only consideration is your girls will transpire more, low humidity and constant circulation. Even then not an issue provided they're not taking more nutes than they can handle. nute strength can be adjusted for low humidity/high transpiration.
 
Dr. Who

Dr. Who

Well-Known Member
Six9 said:
Nice setup OP, sounds like keeping intake and exhaust running 24/7 will do the trick, 25-28 % humidity in flower is nice. Only consideration is your girls will transpire more, low humidity and constant circulation. Even then not an issue provided they're not taking more nutes than they can handle. nute strength can be adjusted for low humidity/high transpiration.
Click to expand...
Low RH is not a good idea......You want to keep in a balance zone.
That's called the VPD or vapor pressure deficit.

Here's chart for you.



You might consider Humidifying the whole house if you own.

Mist humidifier's are inefficient. Look to an evaporative model for a large space and run it IN the room. The room is where you're drawing from and trying to humidify the tent is simply shooting yourself in the foot with exhausting the way you do.

If I recall right, Penny's has a whole room evaporaitve for up to 700 sqft for less the 90 bucks!

Get you RH up for better, more consistent results!
 
Deathhasnofriends

Deathhasnofriends

Member
So if I get the humidity up in the room I'm drawing the air from the humidity in my tent should rise even with exhausting the air in the tent? My air exchange in the room is 205 cfm for intake and 175 cfm for exhaust my tent is a 8x4x7 with 2 air cooled 1000w hoods.
 
Deathhasnofriends

Deathhasnofriends

Member
Dr. Who said:
Low RH is not a good idea......You want to keep in a balance zone.
That's called the VPD or vapor pressure deficit.

Here's chart for you.



You might consider Humidifying the whole house if you own.

Mist humidifier's are inefficient. Look to an evaporative model for a large space and run it IN the room. The room is where you're drawing from and trying to humidify the tent is simply shooting yourself in the foot with exhausting the way you do.

If I recall right, Penny's has a whole room evaporaitve for up to 700 sqft for less the 90 bucks!

Get you RH up for better, more consistent results!
Click to expand...
Also where am I supposed to be on this chart I see the white the Orange the dark blue and light blue what do the colors and #s mean? Thanks in advance.
 
Dr. Who

Dr. Who

Well-Known Member
Deathhasnofriends said:
Also where am I supposed to be on this chart I see the white the Orange the dark blue and light blue what do the colors and #s mean? Thanks in advance.
Click to expand...
Temp of your area on the left. Go across to the right till you hit the orange for "optimal" RH on the top. White area is acceptable!Light blue (higher RH) is better then dark blue (low rh)!

You draw air from the tent and simply run the line BACK into the tent to exhaust? NO, no! bad! Exhaust to room or better yet right out of the room to the out side by a "dryer vent" (camo) exhaust.....Or into the basement is another choice.....Better be sure you control the odor well..
While many don't agree with the practice. I've seen another vent fan near a bigger Filter OUTSIDE the tent that the air passes through again before being exhausted into the house...It works well for this guy......
Another odor control maybe an ion air cleaner after the filter in the line......That stuff's another topic though.
 
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S

Six9

Well-Known Member
Dr. Who said:
Sorry, have to sign off a while - got an appointment. I'll be back in awhile.
Click to expand...
Thanks for the chart! What's the numerical value in each block. VPD? if so wow what's that?

Edit: I found the article at just4growers, reading now many thanks
 
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Deathhasnofriends

Deathhasnofriends

Member
Dr. Who said:
Temp of your area on the left. Go across to the right till you hit the orange for "optimal" RH on the top. White area is acceptable!Light blue (higher RH) is better then dark blue (low rh)!

You draw air from the tent and simply run the line BACK into the tent to exhaust? NO, no! bad! Exhaust to room or better yet right out of the room to the out side by a "dryer vent" (camo) exhaust.....Or into the basement is another choice.....Better be sure you control the odor well..
While many don't agree with the practice. I've seen another vent fan near a bigger Filter OUTSIDE the tent that the air passes through again before being exhausted into the house...It works well for this guy......
Another odor control maybe an ion air cleaner after the filter in the line......That stuff's another topic though.
Click to expand...
No I run air in to the tent from another room and exhaust the tent in to the addick I bought a 4000 square foot evaporative humidifier and now keeping the flower tent at 55% RH and 78℉ thanks for all your help.
 
nomofatum

nomofatum

Well-Known Member
Dr. Who said:
Low RH is not a good idea......You want to keep in a balance zone.
That's called the VPD or vapor pressure deficit.

Here's chart for you.



You might consider Humidifying the whole house if you own.

Mist humidifier's are inefficient. Look to an evaporative model for a large space and run it IN the room. The room is where you're drawing from and trying to humidify the tent is simply shooting yourself in the foot with exhausting the way you do.

If I recall right, Penny's has a whole room evaporaitve for up to 700 sqft for less the 90 bucks!

Get you RH up for better, more consistent results!
Click to expand...
I have to say I'm not liking that chart at all.

If I'm reading that correctly it says 60-80 RH in the lights on temp range and 45-55 in lights out temp range. If I ran at those RH values, I would expect at least half of my bud to be moldy. The windows in the house would ice shut from humidity.

Low RH also is a stimulant for cannabis to produce more resin. UVB and dry conditions require the plant to protect itself with resin.

I run in 30-40 RH, then drop it into the 25-30 RH for the final week.
 
superbak3d

superbak3d

Well-Known Member
nomofatum said:
I have to say I'm not liking that chart at all.

If I'm reading that correctly it says 60-80 RH in the lights on temp range and 45-55 in lights out temp range. If I ran at those RH values, I would expect at least half of my bud to be moldy. The windows in the house would ice shut from humidity.

Low RH also is a stimulant for cannabis to produce more resin. UVB and dry conditions require the plant to protect itself with resin.

I run in 30-40 RH, then drop it into the 25-30 RH for the final week.
Click to expand...

No, that chart is a guideline of what your RH should be at any given temp.

The orange is your recommended ranges, white is safe, anything in the blues will have negative results.


This is very important for certain growers that have to deal with extreme temp changes, mainly due to region. For instance, I am a far northern grower, it's dead of winter right now, and tents get cold fast. Southern growers might have to deal with much higher temps. Cannabis is very adaptable to it's environment.

So, with this chart. If I'm dealing with cold temps, under 60F, so long as my RH remains within 40-55%, my plants will not be harmed.

As you can see, the hotter your temps, the more narrow the optimal RH range becomes. If your temps are between 80-90F, you can still grow just fine, so long as you maintain a higher RH of 80-85%.
 
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