Keeping my fan and filter on

So I kee my fan and filter on 24 hours a day while plants are in the tent. I usually do this so when it’s hot weather it keeps the heat sucked out. Yet during the winter I now use LED lights which produce basically no heat so I have to place a space heater in the tent to maintain temp. Do I need to keep my fan and filter on during cold weather since it’s sucking my heat out making my heater always be on.

It’s always a good idea to keep good airflow to keep CO2 levels the same as that outside the tent. If temp and humidity become challenges, I would favor keeping temp and RH in a good range.

I recommend leaving the fan on at a speed that = the cubic foot of the tent because…

Photosynthesis requires carbon dioxide (CO2), which enters a plant through its stomata. In most plants, photosynthesis fluctuates throughout the day as stomata open and close. Typically, they open in the morning, close down at midday, reopen in late afternoon, and shut down for good in the evening.

Carbon dioxide is plentiful in the air, so it is not a limiting factor in plant growth. However, it is consumed rapidly during photosynthesis and is replenished very slowly in the atmosphere.

Tightly sealed environments may not allow enough outside air to enter and thus may lack adequate carbon dioxide for plant growth.

Stagnant air will allow for microclimates to flourish between leaves and buds. Proper airflow keeps problems like bud rot from developing.

A grow space’s volume is also the required fan cfm rating to exchange air every minute. For example 3ft x 3ft x 7ft = 63 cubic foot. You will need a 63 cubic foot per min (cfm) exhaust fan to remove CO2 depleted air and draw in CO2 rich air.

You’ll also have to account for the ducting, carbon filter, and other accessories you might add which will decrease an exhaust fan’s performance. Add 20% for ducting, 60% for a carbon filter, 50% for a light, etc. For example in a 3x3x7: 63 cfm x 1.2 x 1.6 x 1.5 = 182 cfm exhaust fan minimum*.

Note: a 204 cfm exhaust fan in this 3x3 tent it would have to run near max speed. Choosing a higher cfm exhaust fan (such as a 400 cfm) than the space and equipment requires allows you to run it slower.

Use recirculation fans to ensure the clean air drawn in by the exhaust fan is moved under and over the plants so they can use the CO2.


Leave fan on, like both said above air flow important, take filter off, if on for smell, not needed tell later on. In my 4x4 I have a 4ft tall tower fan, 2 metal 12 inch fans, plus my 6 inch inline exhaust fan. All run 24/7 365, just different levels. Now I’m in winter all on low, just enough to keep air moving. Good luck

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In the winter I have my lights on at night when my house is cooler and off during the day


Keeping my exhaust fan all the time with the circulating fans reduces my RH to <20%. So I have programmed my circulation fans to run in 1 hour increments 3x a day. My exhaust fan now runs 1 hour every 6 x24. Thoughts?

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Damn you guys got super technical on me which I wasn’t exactly expecting lol. I knew I had to keep the airflow going which is why I didn’t bother with turning it off and just keep my heater on constantly. It’s been in the like 20s and 30s here and they are in my garage so I won’t risk the temp dropping.

Here a pic of Amazon shopping chart, those ink bird thermostat can help with that, im trying to upgrade my step up, make it more automatic.