Is my exhaust fan needed?

[Makeminefullgrown]

I recently got back into growing, but all of my experience is outdoors. I’m trying to get things dialed in and grow a few plants under a HLG 320 LED.
My space is a 2’x6’ closet w/ 8’ ceilings. It’s located in a small guest “house” just behind my home. The structure is only one large room with the closet and I use it for my home office.
When I set it up I figured I needed an exhaust fan to pull in new air and blow out the old. So I installed a 6” hurricane fan that is vented into the “attic” space….but it’s not really an attic. For our purposes just assume it’s routed straight outside. I don’t have an intake fan or vent. There is a sizable gap under the door and it passively serves as the conduit for new air.
I run the exhaust 24/7 because I figured I needed to. It’s so powerful it sucks all the humidity out of the space. It’s winter here and the air is cold and dry. I’ve had to run 2 and sometimes 3 humidifiers in the closet just to get my RH to acceptable levels……my plants are in their final days so I’m keeping my RH around 40%.
My question is do I need the exhaust fan at all? I’m opening the door to look at the plants multiple times per day. Plus I’m in the office quite a bit.
I would rather run a CO2 tank than continue with this exhaust and monitor these humidifiers, which need filling twice a day.
I bought a speed controller for the exhaust and it helped but not enough.
Someone suggested putting the exhaust on a timer but I can level out the temp and RH if the exhaust is off.
So, do I absolutely have to use an exhaust fan? I’m not worried about the smell.
If i don’t run the fan should I still leave the area vented? I run two oscillating fans to keep the air moving.
I’m just confused about what the plants really need. Any advice is appreciated. Thanks

 

[nivek]

your situation is near identical to mine,, oddly so actually. i will suggest that you need the exhaust,, my outbuilding is my 'studio',, your office,, my 3'x10' closet is at the back. i have an exhaust that connects to the whole space and i run it a lot. i have been timing it off and on but really it needs to run a lot. my studio gets very stale and sometimes quite humid (after a watering, i too can barely reach 30rh without a humidifier,, 35 with one, ha).

 

[1ne eye]

Maybe be better with a 4 inch exhaust fan with controller, just a thought.

 

[AdaminCO]

I don’t run an exhaust fan until late flower when I’m trying to keep the humidity down.

There are a lot of different variables you need to achieve before CO2 is beneficial. Usually require higher temps too.

Just get a small 4” and run it on low and see where you’re at. It will be great to run with the other fan to fine tune your humidity when you need it more in flower. Be sure to have good air flow.

Here’s a good VPD chart to use for a guideline reference to where your RH:Temp should be.

Stage of growth is at the bottom, reference temp, then cross reference ideal RH. It’s difficult to get it exact, but the closer the better.

I’m at 61%~71F.

 

[Makeminefullgrown]

Maybe be better with a 4 inch exhaust fan with controller, just a thought.

I hear ya. I’ve bought 2 different controllers….one was very cheap and didn’t slow things down at all, but made the fan hum and rattle. The second one was a little more expensive and slows it down considerably, but still not enough. The controller I need is about $50 off Amazon and I’ve been meaning to grab it. It actually changes the Amps, which my electrician friend says is better and won’t harm the fan itself. He says those cheap ones can ruin the exhaust fan.
Right now I’m just trying to get to the end of this current grow. Damn plants are taking their sweet time and just don’t wanna finish.
I probably won’t really need the exhaust for the first few weeks of the next run…..I’m gonna shoot for 81-82f and 65% RH for veg. I see good grows all the time w/ temps in the lower 70s under LEDs, but I’m being told by the folks at HLG (my brand of light) that everything will run better if the air temps are in the low 80s.
With temps that high your RH has to be pretty soupy….like a rainforest.
I imagine I’ll have the opposite set of issues come summer when it’s 90-95f outside and heavy humidity. Will be swapping out the humidifiers for the dehueys I guess.

 

[Makeminefullgrown]

I don’t run an exhaust fan until late flower when I’m trying to keep the humidity down.

There are a lot of different variables you need to achieve before CO2 is beneficial. Usually require higher temps too.

Just get a small 4” and run it on low and see where you’re at. It will be great to run with the other fan to fine tune your humidity when you need it more in flower. Be sure to have good air flow.

Here’s a good VPD chart to use for a guideline reference to where your RH:Temp should be.

Stage of growth is at the bottom, reference temp, then cross reference ideal RH. It’s difficult to get it exact, but the closer the better.

I’m at 61%~71F.

So according to this chart my temp of 74f with a 40% rh isn’t too bad….I’m in late, really late flower. These autos have been flowering for 12 weeks…..growing for 16 weeks since sprout. I have to be approaching some kind of record. At the rate they are changing one will be ready any day, one needs another 8-10 days, and the other needs a solid 2 more weeks if not longer. They just keep spitting out white pistils and the hairs don’t wanna recede. Trichs are just as stubborn. Mostly milky but still some clears and almost no ambers. Whoever heard of a 20week auto flower?? I’m kinda stubborn too and won’t chop before they’re totally ripe. It is leaving me scratching my head.

 

[AdaminCO]

So according to this chart my temp of 74f with a 40% rh isn’t too bad….I’m in late, really late flower. These autos have been flowering for 12 weeks…..growing for 16 weeks since sprout. I have to be approaching some kind of record. At the rate they are changing one will be ready any day, one needs another 8-10 days, and the other needs a solid 2 more weeks if not longer. They just keep spitting out white pistils and the hairs don’t wanna recede. Trichs are just as stubborn. Mostly milky but still some clears and almost no ambers. Whoever heard of a 20week auto flower?? I’m kinda stubborn too and won’t chop before they’re totally ripe. It is leaving me scratching my head.

I had a Sativa Hybrid AK X Grape ape that flowered for 19 weeks. It was brutal but worth it. It was a photo though.

Maybe start giving it an extra hour of dark and drop your temps some to trick it into finishing of quicker?

 

[Vegan4life]

I have a 8" AC infinity exhaust fan that came with a controller. You can set it to run by high or low temp or high or low humidity. I set exhaust to turn on at 76 degrees and it turns off at 75 degrees. I have a passive air intake with a filter for make up air. I run 3 HLG 260 watt fixtures.