Inline Fan question...

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Well-Known Member
Feb 27, 2011
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Hello All,

I'm currently growing out of my closet but my room size is approx. 10x10x8 feet. Therefore, the total 800 feet. If i divide it by 5 (5 minutes to completely exchange air), it equals 160 cfm.

Should I buy a 4-inch inline fan with 170 cfm or buy a 6-inch inline fan with 424 cfm. The 6-inch fan is about $80 more expensive. Is it worth the extra money? Or should 4-inch inline fan with 170 cfm be enough? Of course, whichever fan I buy will have a charcoal filter for the odor.

I'm a little worried about my closet's temperature as we near Summer. Would the 424 cfm fan decrease the room temperature more than the 170 cfm fan?

Temperature, ventilation, and air exchange are becoming a problem.

Also, I created a 4-inch vent to the outside. Would there be any problems with buying a 6-inch fan? Or does the vent size have to be increased, if I buy the 6-inch fan?
Whenever you reduce the size of the fan outlet you will create back pressure and more than likely significantly increase the noise of the fan.

The 6" fan will improve the ventilation and reduce temperature over the 4" simply due to the sheer increase in volume, it will do a much better job of maintaining ambient temps.

Are you pushing the air through a cool tube and or pulling it through a carbon filter?
Use a 6" fan and duct work and your plants will show you their love. Te more air you move thru the growing area the cooler it will be and the more co2 that will be available for the plants
Thanks for your responses....I will be using a carbon filter...HTG has some at pretty decent prices. As such, I believe I will order the 6-inch fan/filter.

The only problem is modifying the 4-inch duct vent to a 6-inch vent...I'm not very handy and was very proud of myself with creating the 4-inch duct...I hope I don't mess it up. I'll let you guys know how it goes.
In my thinking if it's worth doing its worth overdoing, I went with a huge fan for the room size, with 8 inch ducts. I'm gonna try and add a linc to it here cause I've never tried it, I'm computer lame, but anyway I control the temps in here with a variable controller, i slow it way down when the weathers cold, my intake come through screens in the old heater vents in the floor,
Hey Carlo, I just ran into a problem in my new grow rooms that I'll pass along to you.

You may want to buy the air-cooled lights. I intend to run a 500 cfm fan through my lights from the main room and back into the a/c cooled main room. I haven't done it yet, (waiting for the money), but from folks who have used this method, I've learned that it will radically lower the heat problem I'm having.

For now, I've had to reduce the amount of lights and I have to keep a large pedestal fan right in the doorway during "lights-on" time. This draws enough cooled air in to keep the room at 76F.
I've seen that there are 2 kinds of carbon filters for 6-inch fans at HTG... One is called the TallBoy and its pretty big. It only cost $10 more. Is this the filter that I want or just buy the normal size 6-inch filter?

StoneyBud, I was considering doing your method of having the air simply exhaust out from the bedroom and into the house. I also have a.c. in the house. But, I'm thinking that having the air leave the house entirely is the best option for me and therefore I must focus on also killing the odor.

Time is becoming a bit of a problem. I have 1 girl that's has 7-weeks of vegetation and several others are 6-weeks of vegetation...I'm trying to have the flowering closet ready by next Saturday. Once the girls are transferred to the flower closet, I'll do the same fan/odor control for vegetation room.

I didn't know that plants that weren't in the flowering stage could smell so stinky good....But it's becoming a concern.

Once again, thanks for the input.

You can get 6" to 4" duct reducers from any air conditioning supply store, they are a pretty common animal. If you haven't got one nearby try eBay.
Carlo said:
I didn't know that plants that weren't in the flowering stage could smell so stinky good....

Man, that is one of the best parts of growing. When I first open one of the grow room doors at "lights-on", the smell of the plants that have been closed off is the best smell in the world. When they get into the middle stage of flowering, its almost unbelievable, its so awesome.
I would go with the 6" fan and be sure to also order a speed controller for the fan.
Hey THG, do those speed controllers work on any inline fan? I could use one of those.

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