Grow Q&A: Choosing Your Growroom Exhaust Fan Size

Dear Dan, I was wondering if you could give me a ventilation tip…

I’m switching my 10’ x 10’ grow tent from a sealed room to a ventilated one. Every time the AC kicked in the tent would be squeezed inwards and it just doesn’t seem right. So instead of running the AC all the time I would rather ventilate the tent really well. What size intake and exhaust fans would you recommend? I have a 1000 watt, 2 600 w, and a couple of induction 420 lights. Should the intake and exhaust be the same rating CFM, or should I intake less and exhaust more. What would you do? – theCatica

Dear theCatica,
With growroom ventilation, you’re trying to do two things: remove spent air and heat as well as provide fresh cool air to your plants. You want to be able to clear the air from your growroom in about 5 minutes. Any quicker and you risk dehydrating your plants, and longer and growth will begin to stagnate. There are several other factors to consider such as whether your lighting is air cooled and vented separately but I’m going to assume it isn’t.

For a 10’ x 10’ space, assuming you have 8 foot ceilings, you’re cubic footage adds up to 800 cf. This means you’ll need an exhaust fan with a cfm rating of around 160 in order to remove the air every 5 minutes. Keep in mind that any carbon filtration will slow your airflow significantly so boost your rating accordingly. I recommend 240 cfm exhaust fan for your space through a charcoal filter.

Pulling out air stronger than you draw it into your space will create negative pressure and pull extra air through any cracks cutting down on the amount of odor that can escape. Make sure you have at least one oscillating fan per 4 square foot area so you’ll need about 3 of those strategically placed to distribute the fresh air drawn from the lower part of your growroom and expelling spent air from the highest point (because as we learned in school – heat rises).

Have a grow question? Ask away at deardanko@hightimes.com