I had to upgrade my exhaust fan due to heat, so went up from 95 to 195 cfm through 4” duct. The intake fan is 95 cfm. Will this cause issues with one pulling air out faster then the intake brings in? Better to just eliminate the intake fan? Thanks.
The exhaust fan will pull what it needs using the intake as the source. Might be better to pull air directly without an intake fan at all. Take it out and see what sort of flow you get through the intake port/hole/duct/window.
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I never use an intake fan. A good exhaust and passive intake works well, at least in my setup.
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Same, I’ve never used an intake fan…
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Awesome thanks y’all!!! I’ll remove the intake fan. Does it make a difference to add a duct on end of exhaust fan inside grow tent and run it to on top of the light? So the suction is directly next to the light itself? I’m looking to shave off every single degree I can
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Don’t you have a carbon filter? Also if you draw air from the floor openings and exhaust out the top you will get the best cooling effect. Cool air being drawn in, going across your lights and hot air pulled from top of tent.
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I prefer to run a 2" smaller fan for intake. Than I do for exhaust. I’m not sure if I said it right but let’s just say I use an 8" exhaust and a 6" intake.
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I use intake fans only if I dont have a good source of fresh air for my exhaust fan to draw from.
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Yes I do have a carbon filter. I’m not going to use it though until the plants get extra smelly since I’m exhausting straight outside and have very few neighbors out in the country. the exhaust is up top and the intake holes coming from the bottom of cab. As long as this fan can pull the hot air out. I got the Vivosun 4” 195 fan. It’s replacing a computer fan I had and the temps were 92 inside there. Cab is inside a shed with no ac. The intake is located in the shed but I’m going to run a duct to outside. It’s actually cooler outside in the shade then pulling the air from inside the shed. Hopefully that makes a difference too
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I use intake fans, was less money then a split, i dont sell my stuff so what it cost to produce is important to me. They solved a heat problem in the summer for me, the intakes are filtered and dont blow directly on any plants
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I do want to use the intake just for the extra push, I just didn’t know if the weaker intake would cause stress on the double cfm exhaust. Cab is sealed so I’m thinking it would cause a negative pressure? Maybe I’m just over thinking the whole thing
How big is your intake opening?
Mine is like 5x9” and it’s fine for my 4” exhaust fan.
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You ought to be fine with or without any sort of intake fan. A 4-inch duct will move just under about 400cfm so your exhaust fan is sized fine, just need to ensure you have at least the same size intake available Personally do not see any advantage to running a intake fan unless the source air has to be pulled from a (very) long way away.
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My opinion is ditch the 4" all together if youre having heat issues. The cfm it claims is probably twice what it actually moves. With a carbon filter youll be cutting that by 30-40% as a rough guess.
6" or bigger fan will change things a lot. I run minimum 6" full blast 24/7. No need for intake fan. If the exhaust is actually moving air it will pull plenty fresh air through intake screens.
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A million dollar 4" aint moving 400 cfm. Most barely can move 100cfm in reality
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My bad, I meant the duct size of 4-inch can move 400cfm (actually 395cfm). My point was that if he has a 4-inch intake vent he is still nicely below the capability of the exhaust fan.
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My 4" cheap on is 190 cfm, my more expensive Cloudline is 205 cfm but much quieter.
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And now that I look closer – the capacity numbers for a 4-inch duct seem to be all over the place. Once chart says 395cfm – others say (a more rational) 200cfm or so. Sigh…
Regardless the rating I take it more simply – I install my exhaust fan and leave a wide-open intake source. Then I close off that source and listen to see if the fan changes speed at all. Scientifically proven as the extremely lazy stoners way to gauge air flow (smile).
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Yeah ac infinity is a good fan. Got one i havent used other than to test. Much better than the $20 fans. Im waiting for my cheapo 6" to fail before i swap em but 6" is minimum i use now. I was burning cheap 4" ones up. A lot of those 4" dont move nearly what they claim then if you hook a filter to it its about useless. I like lot of air exchange.
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No need for an intake fan - just upsize your intakes and ease the load on the exhaust fan.
I ran that fan in my micro cab with 4 feet of 4" exhaust, so I had (2) 4’ ducts for passive intake down low.
Also, those intakes pulled fresh air from outside, and I ran my lights at night – had pretty even temps.
AC Infinity’s site has a pretty good calculator that factors things like filters / bends / run length etc. to project how many CFM you will want.
I’m sure you already did this - but make sure your fan / filter are mounted as high as possible to extract the hottest air.
Edit - link to the calculator:
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