Filter and Duct Questions

I have a couple questions regarding ducting and the filter.

Does it matter where in the tent the filter is placed (does it need to be at the top, can it be in the middle, can it be at the bottom)?

How important is negative pressure? My old grow setup I used the same ducting, filter and fan and it created negative pressure that obviously sucked air into the tent. You could visibly see the tent suck in. I have since extended the exhaust fan and it no longer seems to create as much negative pressure…will this be an issue, if so, should I add a second fan to pull air to create the negative pressure?

BTW I am using 6" ducting.

The filter is ideally placed at the top center of your tent. I do this, and I have my incoming air going in through one of the tent’s bottom port.

I don’t run a whole lot of negative pressure in my tents. I run just enough to suck in the sides of the tent slightly so that the smell is unlikely to find a place to creep out of the tent. It works great.

I have a 5x5 and one exceptionally nosy neighbor. I run an 8" AC Infinity carbon filter at the top center. I also have an 8" AC Infinity blower pushing air in through a bottom port. I set the input air one notch below my carbon filter and it pulls a slight vacuum on the tent.

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If your goal is pull hot air out of the tent, you will want your ducting pulling from the top of the tent. By removing the hottest air from the tent, you may be able to run the fan at a lower speed and still maintain an ideal temperature.

A little negative pressure helps ensure discretion in terms of smell. If you’re losing precious volume inside the tent because the negative pressure is sucking the sides in, it’s time to figure out a better way.

If you have a way to run an intake duct near the bottom of the tent, that will pull in cooler air without restricting too much. I would filter the air coming in. Minimally, a bug screen would work, but you can jury rig a filter from furnace filters and pantyhose if need be.


Awesome everyone! Thanks for the input. I do have a second 6" fan that I could use on the intake. Currently my filter is pretty low, but maintaining about 74 degrees.


In my 9×9 sealed grow room is it ok to have the can fan intake filter inside the room. will there be a problem getting contaminates inside when changing the filter?

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Welcome to the forum @Grobro
You should be just fine. Filter will not contaminate your space when changing. Might drop a little dust but not enough to be a problem. You probably wont even see any.

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Thanx spinney, I was also wondering if there should be some kind of bug screen on the exhaust? There is a scrubber online ahead of the fan.

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There’s no reason to filter your air as it’s being exhausted in this instance. When you say “scrubber” do you mean a carbon filter?

Yes, it’s to keep the odor down.,bt it’s not on all the time. Just removes hot air.the intake is cool basement air. Just wondered ifbugs could get in when it’s off .probably a dumb question.

I don’t see how they’d bypass your intake filter, but pests are pernicious. I like the idea of a big screen to prevent issues, but it will definitely decrease efficiency to degree. You could use a dryer-vent that closes when it’s off. It will still affect efficiency.