Humidifier/Echaust question

[Avering]

I have a few tents, and I’m noticing that the exhaust fans I bought from ac infinity suck out so much air even in the lowest setting. I open up the intake holes on the bottom of the tents (just one hole open on each tent). The humidity is sucked out quickly, as well as the hot air. I’m wondering how well will the plants veg without an exhaust fan? I either have my mini split ac on or leave the windows open as the temps outside are in the 70s. I understand that you want an exhaust for flowering, but for veg is it really necessary? Could it be better to just put a small fan to move the air around in the bottom of the tent and leave a hole open up top for the hot air to escape?

 

[Rocket Soul]

Yo always need exhaust or humidity will slowly rise to 100% or close to it. I guess if you open every once in a while the tent but really some exhaust is necessary.
You can try extracting from the bottom and intracting from the top; this will keep the tent more hot and moist

 

[laddyd]

Your plants need fresh air to thrive. I've always heard the air in your tent should exchange at least once every minute.
The conundrum is how you balance air exchange with temperature and humidity levels.

 

[Rocket Soul]

Your plants need fresh air to thrive. I've always heard the air in your tent should exchange at least once every minute.
The conundrum is how you balance air exchange with temperature and humidity levels.

Im pretty sure you can go lower; the real trick is to renew the cannopy air environment: theres always higher rh and lower co2 in the cannopy but air movement with fans under cannopy work wonders.

 

[Jimski]

For my situation ( cold basement ) I pick one enviromental point I can control well and base setup from there.
Had a problem with a humidifier tracking poorly, RH was up and down 5-6% but temp was easy I could get that within .3 f so by playing with the humidifier I got a nice 1.5% up and down by ensuring as soon as the fan comes on the humidifier starts regardless of current rh. Small 110v relay energizes the humidifier when fan is triggered.
Now as soon as my infinity shipment gets here I can get the 30% of my tent footprint humidifier back in the sick room.

 

[Delps8]

A grow space should have fans blowing on the plants as well as a fan to evacuate the air in the tent.

Fans blowing on the plants will make the plants stronger and will ensure that the plants have an adequate supply of CO2. Plants take in CO2 during photosynthesis and if that supply of CO2 is not replaced, photosynthesis, and, therefore, growth drops very quickly with just a slight drop in CO2 concentration.

Air in the tent needs to be changed to ensure that there's adequate CO2 but also to remove moisture laden air from the tent.

There are two categories of cannabis growers - those who have lost a crop to bud rot and those who haven't (yet) lost a crop to bud rot. I'm in the first category but learned my lesson.




I tried to get an answer re. how much air to move through a tent and found a variety of opinions:



The numbers at the bottom are for my 2' x 4' x 8' tent and the AC Infinity 4" inline fan. At a setting of 4, that fan will evacuate the tent once per minute.

The table on the right shows that if you want to change the air every two minutes (which is changing 0.5 of the tent /minute) that's 32 cubic feet/minute and the fan will do that at a setting of 2/10.



And in plain text so you don't have to type in all the links:


∆/minute
Min Max
0.2 Air in your grow area should be exchanged at least every 5 minutes.
https://hydrobuilder.com/learn/grow-room-atmosphere-ventilation/
#:~:text=Air%20in%20your%20grow%20area,feet%20per%20minute%20(CFM).

0.2 For growing crops, it should be a minimum of once every 5 minutes…
https://www.hydrotekhydroponics.com/cfm-calculator

0.33 1 All the air in your grow tent should be replaced every 1-3 minutes for the best results so ideally,
you should replace the air every minute unless you live in a place where the conditions are not too harsh…
https://2fast4buds.com/news/the-importance-of-air-circulation-in-indoor-cannabis-grow

1 For optimal growing conditions, changing the entire airflow circulation
of the growing area at least once every minute is recommended.
https://sensiseeds.com/en/blog/grow-tent-ventilation-how-to-calculate-your-needs/

0.33 3 A grow room of e.g. 8m³ would need a fan that could extract at least 8m³ per minute
and possibly 2-3 times that if you grow in summer or a warm grow room.
https://dutch-passion.blog/cannabis-grow-room-ventilation-guide/

1 Ideally, you’ll want the air in your grow space to be completely renewed every minute.
https://www.cannaconnection.com/blog/19407-cannabis-grow-room-ventilation-full-guide

1 This will ensure your fan completely replaces the air in your grow space every minute.
https://www.royalqueenseeds.com/us/blog-ventilation-guide-for-your-marijuana-grow-op-n738

1 Since a grow space’s volume is also the required CFM to ventilate it every minute…
https://acinfinity.com/pages/grower-setup/grow-tent-ventilation.html

Total minimum air exchange required = 16
https://cannabistraininguniversity.com/required-air-exchange/

1 the exact air flow you need to change the air every minute.
https://www.globalairsupplies.co.uk/how-to-calculate-a-ventilation-system/

0.33 1 fresh air should be circulated into your grow space every 1–3 minutes.
https://www.zambeza.com/blog-the-importance-of-airflow-when-growing-cannabis-n199

0.33 The rule of thumb here is that you need an exhaust fan that can exchange the
ir in your grow tent/room at least once in every three minutes.
https://thehippiehouse.com.au/blogs/news/calculating-your-grow-room-fan-size

 

[coreywebster]

I have a few tents, and I’m noticing that the exhaust fans I bought from ac infinity suck out so much air even in the lowest setting. I open up the intake holes on the bottom of the tents (just one hole open on each tent). The humidity is sucked out quickly, as well as the hot air. I’m wondering how well will the plants veg without an exhaust fan? I either have my mini split ac on or leave the windows open as the temps outside are in the 70s. I understand that you want an exhaust for flowering, but for veg is it really necessary? Could it be better to just put a small fan to move the air around in the bottom of the tent and leave a hole open up top for the hot air to escape?

Let's start with what tents you have,
for what purpose is each ?
and what are the temps and rh when lights are on and the extractor is running?

 

[Avering]

Let's start with what tents you have,
for what purpose is each ?
and what are the temps and rh when lights are on and the extractor is running?

I have two 2x3x6 tents, and one 2x4x6. These three are being used for flowering. Then I have one small 2x2x4 to keep some small plants vegging. The temps for two of the flowering tents are 82-84 with about 70 rh. One of the flowering tents stays a little warmer at 85-87 usually and the rh will go a little higher like 75-80, I’m thinking of switching the exhaust fan cause it’s quite weak it seems. The smallest tent for vegging has all of its bottom flaps open and a small clip on fan on the hole pushing air down. i try to have all the flaps open on the bottom of the tents for fresh cold air to come inside but I’m careful because I don’t want light to hit inside the tents during dark periods

 

[coreywebster]

I have two 2x3x6 tents, and one 2x4x6. These three are being used for flowering. Then I have one small 2x2x4 to keep some small plants vegging. The temps for two of the flowering tents are 82-84 with about 70 rh. One of the flowering tents stays a little warmer at 85-87 usually and the rh will go a little higher like 75-80, I’m thinking of switching the exhaust fan cause it’s quite weak it seems. The smallest tent for vegging has all of its bottom flaps open and a small clip on fan on the hole pushing air down. i try to have all the flaps open on the bottom of the tents for fresh cold air to come inside but I’m careful because I don’t want light to hit inside the tents during dark periods

So flowering tents are a bit high rh and veg tent is too low?
You didn't list the rh of the veg tent.

How much vegetation is in the veg tent?

 

[MissinThe90’sStrains]

You can get fan-speed-controllers for your exhaust fans, to dial them back to whatever % you need, to keep adequate negative pressure and environmental conditions.

 

[Star Dog]

I think a fan speed control is a must have item in any grow, I like continuous slow venting due to the high humidity.

It's easier to keep humidity down with continuous venting than let it rise and have to beat it back down with humid air, if I had dry warm air I I'd only need to adjust the fan speed?

 

[MissinThe90’sStrains]

Overall, the less variables you have to deal with, the better. If you can work on buffering your lung room (dehumidifier, temp control, venting into other rooms/outside, or whatever else it may need) it‘l make it much easier to keep all your tents in that happy zone for your plants, even if the individual tents need different specs. Even in veg, you still need to watch your humidity. There are a host of pathogens that like warm and moist conditions, that you need to be mindful of. Also, large swings in humidity and temperatures might contribute to things like dew or condensation which you really don’t want. That leads to things like PM, mold, septoria, and fungal infections that can ruin your grow.

 

[Jimski]

I think a fan speed control is a must have item in any grow, I like continuous slow venting due to the high humidity.
View attachment 5437160
It's easier to keep humidity down with continuous venting than let it rise and have to beat it back down with humid air, if I had dry warm air I I'd only need to adjust the fan speed?

As long as the capacity of the fan is = to or greater than the humidity load from your plants. A cannabis plant in deep flower can consume a gallon of water a day or more. Some is used in production of the plant but most is transpired into the air.
I was told by a grower who did production level grows that one good plant has the humidity load of a gallon of water spilled on a rug.
Every day.
Every plant in deep flower.
Yet another reason to perpetual......

 

[weedstoner420]

I understand the intent of following VPD, but running in the high temp/high humidity end of the spectrum would sketch me out. I'd much rather flower with temps in the mid-70s and RH of 50-60%, than with temps in the 80s and RH of 70-80%.

 

[Jimski]

I understand the intent of following VPD, but running in the high temp/high humidity end of the spectrum would sketch me out. I'd much rather flower with temps in the mid-70s and RH of 50-60%, than with temps in the 80s and RH of 70-80%.

Hopefully the new Infinity AI system will have a subroutine where it tells a grower:
"I can't let you do that Dave"

 

[MtRainDog]

Following VPD is somewhat theoretical too. It's based on lab conditions, and analyzing things at the cellular level. In real life, there's so many more variables. I wouldn't consider chasing VPD and adding CO2 until I was very familiar with a particular plant, and had a sealed environment running like clockwork.

Amazing dope was grown even in the 70's and 80's, and no one growing it was following a VPD chart.

 

[Avering]

So flowering tents are a bit high rh and veg tent is too low?
You didn't list the rh of the veg tent.

How much vegetation is in the veg tent?

The veg tent is around 85-87f and rh is usually 80-82 it’s more like a seedling tent, it’s got 3 small plants now that have been growing a few weeks. The flowering tents are a bit high rh right now but the fans are on low settings so I can adjust it

 

[Hook Daddy]

I understand the intent of following VPD, but running in the high temp/high humidity end of the spectrum would sketch me out. I'd much rather flower with temps in the mid-70s and RH of 50-60%, than with temps in the 80s and RH of 70-80%.

I keep an eye on VPD, but it when it comes mid to late flower I keep temps high 70s to low 80s and rh 45%-55%, lowering rh as they get closer to harvest and denser. Perfect VPD is great, but also great for mold in late flower and not worth the risk imo.

 

[MtRainDog]

The veg tent is around 85-87f and rh is usually 80-82 it’s more like a seedling tent, it’s got 3 small plants now that have been growing a few weeks. The flowering tents are a bit high rh right now but the fans are on low settings so I can adjust it

I would crank those fans. In the warmer months where there's nothing I can do for humidity, the exhaust goes to 100

 

[Jimski]

Following VPD is somewhat theoretical too. It's based on lab conditions, and analyzing things at the cellular level. In real life, there's so many more variables. I wouldn't consider chasing VPD and adding CO2 until I was very familiar with a particular plant, and had a sealed environment running like clockwork.

Amazing dope was grown even in the 70's and 80's, and no one growing it was following a VPD chart.

Look at the specs on the sensors on your temp and humidity. Look at the +- specification.
Now realize that your temp could be 1.3 degrees high or low. Humidity is better but still can be .75% off.
Now look at the vdp chart and see what a mess it is.
Having said that if you target the middle of the chart and go towards a lower temp and RH having an index to compare is the reason to use VDP. Without it growers would have no clue where to even start and face it, Windowsill grows do not have a lot of vdp tracking and some of them looked just fine.