Need help on figuring out my venting frequency and how long of intervals.

Pparker88

Active Member
I have a 4x4x8 grow tent with a 6” fan with 440cfm. I’m using 8 120 QBs with a 240 watt meanwell driver per 4 boards. How often should I be venting and for how long? I’ve looked up different sources and not sure which is best/correct. Can you provide this guy either can answer or solution in a simple and basic way? Like “Venting for Dummies?” Lol
 

Merkn4aSquirtn

Well-Known Member
Well it depends..
Are you planning on running co2?
If not, I'd assume you'd want to run it 24/7.
That size tent could probably use 440 @ 75%
Maybe less.
I adjust until I get a little bit of negative pressure in my tent (the walls start to suck in)
It also depends on your temps and humidity too.
Really, its something you'll have to adjust accordingly to your wants and needs in temp/humidity.
Get a fan controller if your fan doesn't have one.
 

HydroKid239

Well-Known Member
I have a 4x4x8 grow tent with a 6” fan with 440cfm. I’m using 8 120 QBs with a 240 watt meanwell driver per 4 boards. How often should I be venting and for how long? I’ve looked up different sources and not sure which is best/correct. Can you provide this guy either can answer or solution in a simple and basic way? Like “Venting for Dummies?” Lol
Run it constantly, and just adjust it as needed. It's gonna be needed to get the heat out of there. I keep mine on hi in a 2x4 195cfm with a vent open on the bottom for passive intake. I run 211w of LED and temps hovering in 79-82F RH 40% in late flower. I will be running my AC in the room with all vents open to cool the tent down dramatically before chop. I like the cool temp colors.
 

Renfro

Well-Known Member
If you stop venting even when the lights are off you can experience elevated humidity levels that can result in mold / mildew.

What are your ambient temperature / humidity numbers looking like?

The use of an environmental controller can turn the fan on and off depending on the humidity or temperature.
 

Renfro

Well-Known Member
My preferred method would use a titan or autopilot environmental controller and if I needed to slow the fan to reduce CFM/negative pressure or to silence noise then I would add a variac to the equation. With LED you probably don't need 440 CFM to keep the space cool, even with the fan slowed down it would likely still kick on and off via the controller.

Remember that if you are venting to and from the room the tent is located in, you can cause the "lung room" temperature / humidity to rise, diminishing the effectiveness of the ventilation system. If this becomes an issue the simple solution is often to vent the exhaust from the tent directly outdoors.

Using a carbon filter on the exhaust will help eliminate odor.
 

gkay723

Active Member
If you stop venting even when the lights are off you can experience elevated humidity levels that can result in mold / mildew.

What are your ambient temperature / humidity numbers looking like?

The use of an environmental controller can turn the fan on and off depending on the humidity or temperature.
What about if you had to add heat into the room? Would you keep the exhaust on through out the whole night? Or maybe vent once an hour?
 

Pparker88

Active Member
What about if you had to add heat into the room? Would you keep the exhaust on through out the whole night? Or maybe vent once an hour?
i'm waiting on a trolmaster fan controller. i also got a temp controller that i will be plugging a ceramic heater into to regulate temp
 

Pparker88

Active Member
My apologies, I was asking @Renfro a hypothetical question. Trying to figure out my ventilation also.
me, personally, have been venting 24/7, and have used a heater by one of my passive intakes and once the temp goes up, it does a decent job of retaining a little warmth. but i feel like my fan is too efficient, so i'm going to slow it down with a fan controller. then a controller with the heater plugged in and a humidity controller to keep my RH% right.

so far, the cold and humidity(i have seedlings currently) have been my biggest challenges. But i am using a vented humidity dome to keep my RH% in check for now.

do you have a grow tent or room? because i just warm the room the tent is in and warm the tent that way
 

gkay723

Active Member
I'm in a room. I was venting all the time before it got cold. Now I'm venting once an hour at night. 20c 55 -60 rh lights off.

My biggest problem is bud rot. Even with the heat, I can't seem to bring the rh down further.
 

Pparker88

Active Member
I'm in a room. I was venting all the time before it got cold. Now I'm venting once an hour at night. 20c 55 -60 rh lights off.

My biggest problem is bud rot. Even with the heat, I can't seem to bring the rh down further.
have you tried a dehumidifier? heaters also dry out the air a bit.
 

Star Dog

Well-Known Member
I have to run my 6" fan (iirc 660cfm) constantly if the it stops rh starts rising within seconds.

I've used fan speed controllers and environment controller's and found the constant extraction of a £50 variac at 25/40% every bit as good even preferred, i've got my one wired through a heat/cool relay (£10) to automate it, to buy a controller of its equal would cost hundreds of pounds, the last I looked £400 for a hybrid with temp and speed control.

Best of luck with your grow.
 

HydroKid239

Well-Known Member
What about if you had to add heat into the room? Would you keep the exhaust on through out the whole night? Or maybe vent once an hour?
Humidity can be hard to control if everything isn't dialed in, including outside temps & humidity. If your room is humid, and you run an intake you are adding to the tents humidity. Run a small radiator in the tent with a cheap thermostat keeping it around 77 day/68 nights. Then running the intake/extract will suck the humid air out. Just have to set the temp and fans dead correct.
 

Star Dog

Well-Known Member
I'm in a room. I was venting all the time before it got cold. Now I'm venting once an hour at night. 20c 55 -60 rh lights off.

My biggest problem is bud rot. Even with the heat, I can't seem to bring the rh down further.
Having to sacrifice heat for humidity isn't unusual, for the last 4 weeks my room has barely been above 24c and that's with a dehumidifier running, when the light out the dehumidifier + constant slow extraction maintains around 60%/20c its the outside rh that decides the final figure usually 48/60%.
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Renfro

Well-Known Member
What about if you had to add heat into the room? Would you keep the exhaust on through out the whole night? Or maybe vent once an hour?
Do what is required to keep the humidity from creeping up. You don't have to ventilate all night persay, you could use a humidistat. You could use a dehumidifier, that adds heat and dehumidifies. Adding heat is good for humidity as warmer air holds more water. So if you warm the room the RH% drops. Basically if the RH% doesn't rise without venting then you don't need to vent/dehumidify however that is rarely the case. In some cases venting could make the RH% problem worse if you have high ambient RH%
 

gkay723

Active Member
Apologies to op for this question but It is related to the topic. During fall/winter, is it unwise to draw fresh air directly outside into the grow room?
 

Renfro

Well-Known Member
Apologies to op for this question but It is related to the topic. During fall/winter, is it unwise to draw fresh air directly outside into the grow room?
Ive done it a lot, aside from condensation on the duct / blower it's not an issue unless the air is blowing directly on your plants. I blow the air in up high so it mixes with hot air. The cold air will be dry air so thats good, even if it's 100% RH outside, warm that air up and it's negligible water content drops your RH%.
 
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