ok so I’m growing in a 3x3x6 tent with a hlg 550 dimmed down. so with the light dimmed I can keep the temp around 23-25C but humidity is around 70-90 with a lot of condensation on the walls. I got a 6" exhaust fan hooked up to help with smell and humidity and pull in freh air, but it also drops the temp down to 18C when running so I got it on a timer to turn on for 15 min every hour.
so I was thinking getting a new 4" exhaust fan would be the fix, letting it run 24/7 and at a lower speed. just want to make sure that I’m not pissing away more money then I have to. and that the 4" is capable of keeping the smell down and pulling fresh air in.
growing in an unfinished basement and the average temp is around 15C
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Pissing away money is fun though? I would get dehumidifier. My grow is the opposite, I’ve got 2 humidifiers running in my tent.
Could also come in handy when you are curing.
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25c or 77f is not a high temperature. Mine often hit the high 80s. More heat = lower RH. The extraction your using should help stop pm or budrot setting in. I’d have an fan blowing directly across the canopy to help to keep the warm air moving. Watering less often will also help with the humidity problems. My plants are in 3 litre plastic pots with coco as the medium and although it’s suggested to water coco daily mine get watered every 2 - 3 days. I’d also ignore all this watering till run off bollox unless you need to test the run off ph.
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You can just dim your fan, with a 10$ dimmer from Ebay.
No need to buy a 4" fan, a dimmed down 6" fan will run silent and have less weak and tear running on ½ speed.
https://www.ebay.com/itm/110V-220V-Dimmable-LED-Brightness-Dimmer-Ceiling-Fan-Speed-Control-Switch-Set/283320793170?hash=item41f73c3852:m:mtqLbY7KI9FyuI79PnB4vRQ
Another and sweeter option, would be something like this fan controller.
https://www.electricautomationnetwork.com/en/eliwell/fa53370000-eliwell-fasec-33-to?search_query=33+fasec&results=2
Dehumidifyers are a great help as well, but I mainly run mine late in flower only.
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yeah you need a fan speed controller … but w/ LEDs you wanna run temps a little hotter than with HPS to maintain the same leaf temperature w/ the cooler light source … my flower tent runs 85 to even 90 (32.2c) some days
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I do have a variable speed control on the exhaust fan it’s on the lowest it can go. And a 8" oscillating fan in the tent, as for a dehumidifier I don’t have the room in the tent for it.
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tbh i have a 4x4x7 tent and i only have a 4" 192CFM fan and i run that at 50% and it’s got serious negative pressure still
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Sounds like you need to raise the temp a bit inside the tent so you can run the extractor constantly. You can try turning the driver up so your light produces more heat and/or use a couple of those 3’ tube heaters with the fitted thermostats.
I grow in a cold, wet country and sometimes a dehumidifier is essential but if not an option, raise the heat and the extraction rate. Also small(ish) pots of coco help keep RH levels lower along with waiting until they feel quite light before feeding again.
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That’s a better easier to understand explanation of what I was saying in my statement 
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I use a 30 quid dehuey from Amazon. And keep my temps around 24c. It keeps my environment nice. I’d be inclined to raise your temps a touch until you get a dehumidifier to minimise any chance of mold/mildew
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The dehumidifier goes in the room outside the tent (or wherever the air comes from), so the air being sucked in by your fan is dry.
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What @beacher said is best case scenario but if your basement is very large or open to the environment that could be a loosing battle at very high cost. Mini dehumidifiers like the one @anon58740919 is using go inside your tent/space and work on low voltage so are safe for wet conditions , you might need a couple of them if it’s that damp btw.
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I had the same problem here in Canada when the RH went way down in the winter. When my fan comes on it sucks all the RH out of the tent… and temps go really high if fan doesn’t come on. Seems like an impossible situation - but then I heard about INKBIRD - they have very reasonably priced RH and Temp controllers. (Around $60 CDN … for each - or $100 for a unit that does both)!
This solved all my RH and Temp problems!
Here is a link to their controller that does both RH and Temp: Amazon.ca
I did have a cool mist humidifier in my tent, and the Inkbird would turn the humidifier on or off as needed, and then the Temp monitor turns my fan on when the temp gets too high.
Not really that much $$ for piece of mind.
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