Running exhaust fan 27/7 vs intermittently

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dopenixon

Member
Hey fellas just wondering how you guys run your air intake/exhaust in your tent. I am in a basement that is about 68f in the day and 62f at night, so keeping my tent around 70 isn’t an issue with lights on, but it gets difficult to do as the heat from the light is gone and I’m pulling cold air in through the vent holes.

I am using passive airflow so no intake fan and was wondering if I could just crank the inline fan every now and then and give my tent environment time to stabilize to the plants liking, instead of constantly matching my basement. Would this screw the fresh air up?
 
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Triplefastaction

Well-Known Member
Your theory will work fine as long as you are in veg. It will lead to increased humidity levels, which again, in veg, is fine. You do need to periodically exhaust/exchange the air though.

During flowering, you are going to want to keep it running 24/7, otherwise your humidity will explode. Especially when your lights go out. You can’t retain the heat without retaining all the moisture, and that would be problematic.

I grow in similar conditions as you. I typically need to run a heater during lights off at a minimum. In winter, I often have to run the heater during lights on too. Good luck.
 
futurebanjo

futurebanjo

Well-Known Member
I've done it a long time ago, using a segmented timer like you would for the lighting rig.....each switch on the dial represents 15mins so you can alternate each little swich 50/50 or whatever to correspond to light/dark periods.

I just run an extractor 24/7 now though, as it helps my humidity, but also its always passivley pulling in 'fresh' air, so it keeps CO2 levels up/consistent.
 
futurebanjo

futurebanjo

Well-Known Member
Just to clarify, I was runing my extractor all the time with lights on, but in periods of lights off, I had each little switch on the fan timer alternating for that 12hr period... so when it was 'night time' for the plant, the extractor would run for 15mins, and then cut off for 15mins, and then run again for 15 mins, etc..

But you have to be carefull doing that as your humidity might spike up high... you may vary, as always it just depends so you have to keep a close eye on humidity
 
thumper60

thumper60

Well-Known Member
dopenixon said:
Hey fellas just wondering how you guys run your air intake/exhaust in your tent. I am in a basement that is about 68f in the day and 62f at night, so keeping my tent around 70 isn’t an issue with lights on, but it gets difficult to do as the heat from the light is gone and I’m pulling cold air in through the vent holes.

I am using passive airflow so no intake fan and was wondering if I could just crank the inline fan every now and then and give my tent environment time to stabilize to the plants liking, instead of constantly matching my basement. Would this screw the fresh air up?
Click to expand...
What you really need is a dehumidify run it when lights are off along with the exhaust it will warm things up an keep things nice an dry in the whole basement.
 
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dopenixon

Member
futurebanjo said:
I've done it a long time ago, using a segmented timer like you would for the lighting rig.....each switch on the dial represents 15mins so you can alternate each little swich 50/50 or whatever to correspond to light/dark periods.

I just run an extractor 24/7 now though, as it helps my humidity, but also its always passivley pulling in 'fresh' air, so it keeps CO2 levels up/consistent.
Click to expand...
I always thought plants breathe CO2 so I was a bit confused that I’d need to pump oxygen in for the plant. Is there a reason for this that I’m not considering?
 
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dopenixon

Member
thumper60 said:
What you really need is a dehumidify run it when lights are off along with the exhaust it will warm things up an keep things nice an dry in the whole basement.
Click to expand...
I have a dehumidifier in my basement and my exhaust fan exits out of a vent in my basement. If I put it in my tent I think id just be sending the dehumidified air outside. I wonder if it would still help at all in the tent with constant circulation.
 
thumper60

thumper60

Well-Known Member
dopenixon said:
I have a dehumidifier in my basement and my exhaust fan exits out of a vent in my basement. If I put it in my tent I think id just be sending the dehumidified air outside. I wonder if it would still help at all in the tent with constant circulation.
Click to expand...
Just run the exhaust back into the basement with lights out to recirculate the air, no need to exhaust out the building with lights out unless it gets to hot.
 
C

cage

Well-Known Member
dopenixon said:
I always thought plants breathe CO2 so I was a bit confused that I’d need to pump oxygen in for the plant. Is there a reason for this that I’m not considering?
Click to expand...
The cells in the plant need oxygen to use the carbohydrates for energy.
The carbohydrates are made from CO2 during photosynthesis.

If there is no oxygen in the rootzone, the cells suffer and become susceptible to diseases and damage.
 
futurebanjo

futurebanjo

Well-Known Member
dopenixon said:
I have a dehumidifier in my basement and my exhaust fan exits out of a vent in my basement. If I put it in my tent I think id just be sending the dehumidified air outside. I wonder if it would still help at all in the tent with constant circulation.
Click to expand...

What he said above, also air contains oxygen and CO2...only small amounts of CO2, so a constant supply of fresh air will stop CO2 levels dropping.
 
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dopenixon

Member
thumper60 said:
Just run the exhaust back into the basement with lights out to recirculate the air, no need to exhaust out the building with lights out unless it gets to hot.
Click to expand...
The humidity in my basement was getting really high and I read that exhaust straight into the basement could cause mold. I don’t know if it is true or not but it scared me lol.
 
Moabfighter

Moabfighter

Well-Known Member
Get a Dehu and set it to keep your room at whatever you want say 65. Have a controller in your tent to click on when it gets say… over 65. So if your room is at whatever humidity you want and you do this, you can keep your environmentals in check
 
ProPheT 216

ProPheT 216

Well-Known Member
I think most everyone has overlooked what air exchange does. It's not just temp control and humidity control. It's CO2 to the plants. You should be changing all the air in your tent every 2 to 3 minutes. Idk why this fan timer stuff has become such a fad
 
Moabfighter

Moabfighter

Well-Known Member
ProPheT 216 said:
I think most everyone has overlooked what air exchange does. It's not just temp control and humidity control. It's CO2 to the plants. You should be changing all the air in your tent every 2 to 3 minutes. Idk why this fan timer stuff has become such a fad
Click to expand...
If you can keep stable humidity in your room or grow with constant exhaust, heck yeah. It’s also often very dry if you run your exhaust 24/7 without supplementals
 
1

1212ham

Well-Known Member
ProPheT 216 said:
I think most everyone has overlooked what air exchange does. It's not just temp control and humidity control. It's CO2 to the plants. You should be changing all the air in your tent every 2 to 3 minutes. Idk why this fan timer stuff has become such a fad
Click to expand...
I'm curious, where does the every 2-3 minutes number come from? Does anyone know?
 
futurebanjo

futurebanjo

Well-Known Member
1212ham said:
I'm curious, where does the every 2-3 minutes number come from? Does anyone know?
Click to expand...

Standard 'fresh air' is only about 0.04% CO2... so in a small space like a tent, combined with a plant thats activley using up the CO2, you need to maintain a flow of 'fresh' air flow.
That's where the balancing act comes in with humidity and extractor fan speed.
 
ProPheT 216

ProPheT 216

Well-Known Member
Plants use the CO2 immediately around the leaves in less than 30 seconds, with fluttering air and a dense canopy within 2 to 3 minutes your CO2 levels will drastically fall off. It's best to measure cfm after fitted with a filter to calculate how big of a fan needed for said space. Again the goal is a total air change every 2 to 3 minutes based on cfm vs tent volume
 
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