Timer on intake and exhaust fan


This is my first grow and I have a question. Does anyone put a timer on there intake and exhaust fan and why or why not.


I do not, because I like the slight drop in temps at night when the lights go off.

Edit: I should mention, this is my first grow, too. I’m just going off research I’ve done, and my personal experience so far.


@Hippieheart You always want to exhaust old air and intake fresh air. Humidity rises at night (or when plants sleep). Keep your fans on and keep the air moving and you will prevent mold and pest problems!


@Bogleg does to help maintain more steady temps. I’m sure he’ll be happy to explain when he sees the tag.


I personally dont I believe a constant air flow is key to preventing mold or mildew
I do know some will set it up on temp and humidity controls
And you can set timmers to run every 15 min for 5 minuets or something like that if needed
Just make sure heat and humidity doesnt build ip to high during off period


During my girls night time i put my exhaust on low . i use a variable speed with a low & high setting


I personally have my exhaust on the same timer as the exhaust and my charcoal filter. And my intake drops to 25% when lights go off since it brings much cooler fresh air. Im about to let the exhaust off for an additional 2-3hrs when my Co2 comes on and saturates the room for the first few hours the lights come on. I do not have mold or humidity issues.


I have had a pretty cold basement and a super low humidity most of this winter. My gold leaf plant was constantly showing signs of nitrogen toxicity even though I kept nutrients and PH in check. @niala worked with me and we determined the issue was too much air flow. Too much air flow reduced my humidity regardless of my humidifier and kept my tent cooler forcing me to run the heater on high - this meaning I have a major source of heat both above and below the plants. I’m sure that hurt the humidity too.

Most people say you should replace the air every 3 minutes. Well in a typical 4x4 tent is 112 cubic feet. So you only need fans that move 38 cfm. Most of us have 230-440cfm fans.

My solution was to use a timer instead of a potentiometer. I have my fans run for one minute, then shut off for two minutes. By doing this I have my heater at half the power and don’t have to run a humidifier in my tent. I’ve also gotten temps manageable between 60F and 82F.


@Hippieheart I don’t. Intake and exhaust on 24/7. It’s worth the 150 watts 24/7 I use not to have mildew problems and it pumps more CO2 in also.


I use timers 1. Bc my gets to cold right before dawn when filter n exhaust is off that temp stays good. 2. The hours its off the plants are getting pumped with co2 so it lets build up in room few hours then exhaust heat and bring in fresh for warmer hours of the day and so on. When my temps get to high turn it on longer to bring them leave off longer.