10" exhaust for 9x10 room, overkilling it?

[MDT]

My room is 9x10 Feet, running a 10" exhaust fan and a 8" inline fan, is the exhaust too powerful? I'm using the room to veg and I find it impossible to control the humidity and temperature simply because it's sucking everything out of the room. Room temp is where I want it to be at 70-75F, humidity is too low at 34%, I'm using a humidifier but the fan is just too powerful for it to make a difference.

Plants are 4 days into veg and I haven't seen any noticeable growth. Can it be possible that the fan is sucking out air too fast therefore creating negative pressure in the room?

I thought about using a timer to turn the exhaust off every half an hour but I read somewhere that air should be exchange every 3 minutes so I'm debating whether or not getting the humidity up is worth turning the exhaust off?

 

[Whatever]

Can it be possible that the fan is sucking out air too fast therefore creating negative pressure in the room?

You want some negative pressure IMO. Too much is a waste and means you have oversized your exhaust fan. If too much negative pressure and heat issues you've undersized your intake fan.

If plants are 4 days into veg I assume you're running clones. If so no problem as it takes a few days after transplant for them to settle in and kick into gear so don't worry about that one. Just wait a bit.

Sounds like you're running an open system and not much you can do about that humidity. Turning the exhaust off to raise humidity will also raise temps. For veg your temps should be a bit higher. I shoot for 77 but up to very low 80's is OK but not preferable unless you're running CO2. I've run low 80's before and everything was fine. I mean outdoors in the summer it's regularly much hotter.

Shoot for an air exchange every 2 minutes but faster is better if you can maintain temps. I ran open systems and where I live, high desert, humidity would regularly be below 34%. Veg growth will be slower but still OK.

Instead of shutting off the exhaust try a fan speed controller big enough, wattage, to control both fans and slow em down. You're room is 720 cf, I assume you have 8' ceilings, so you're current setup is a bit overkill but in the heat of summer will probably be great.

I now prefer two each intake fans, exhaust fans and carbon scrubbers. Both sets are on independent thermostats set 1 degree apart. Last room was a 300/300 cfm combo and an 900/900 combo. In the summer I needed both running but in the winter, because I was pulling in freezing cold air, the 900 combo rarely ran. The 300 combo was set at 76 and the 900 combo at 77. I ran the hood exhaust fan, another fan, into a cardboard box that encased the 900 combo scrubber. I also had a large hole cut in the box. This way I vented the heat, the intake side of the hoods was open drawing air directly from the room, into the cardboard box. When the room was cool the hood heat found it's way into the room through the large opening. When the room was hot the 900 combo engaged and pulled not only air from the hot room but directly sucked out the heat from the hoods that was ducted into the cardboard box because the hood vent fan was only 300 cfm. This is the setup I ended up with after trial and error to deal with the seasonal differences of sub freezing weather in the winter and 90+ heat in the summer. I also ran a heater lights off in the winter and an ac lights off in the summer. In the Winter I ran lights on during the day and in the summer lights on in the night. A dehumidifier was used year round lights off. That place still needs a few tweaks but it's very close.

Sorry for babbling but bottom line is lights on the humidity was ever it was. It was rarely over 55% lights on year round even if foggy and pouring down rain outside and most of the time it was close to where you're at 35%, and a lot of times much lower. I live in high desert in the mountains.

Hopefully this helps a bit.

 

[MDT]

Your post was very helpful Whatever, I like your ventilation setup, it seems like we have similar weather.
This fan I have is a hand me down and that person modded the fan with a light switch to control the speed, one for low and one for high. Since it's not a proper fan controller, I wonder when the switch is on low if it's actually the lowest possible?

I've decided to let the exhaust run at 30 mins interval. Just found the specs of the fan, it's 1000CFM, an overkill considering a room of my size only need about 480CFM.

Does anyone know what negative effects of using an oversize fan has on a room environment? I'm guessing the co2 is being sucked out too quickly for the plants to use them?

 

[Whatever]

I'm guessing the co2 is being sucked out too quickly for the plants to use them?

If the CO2 is getting sucked out it's getting replaced just as fast. In one room I had an air exchange every 45 seconds. In the dead of winter the room would feel and smell like a fresh spring day. It appears it's gonna take you awhile to get up to speed and that's fine. The CO2 level in the room was the same as outside and in my experience outdoor plants do just fine.

How are you going to cut the ventilation for 30 minutes without the heat going through the roof? How many watts are you running? This is an open system...right? Are you attempting to inject CO2? What the heck are the details on your setup? By cutting off the air for 30 minutes the CO2 in the room will steadily drop as the plants use it up. Right now they sound small so no biggie at this stage though. You're too concerned about the humidity which you think is too low. Yes it would help if it was higher.

I keep on showing the same pics here but whatever...lol. Here's stuff grown in a room where the humidity was lower than what you're dealing with. How do you think they turned out?

Invest in a good speed controller as they are not that expensive. Cutting the flow of that fan in half should help out. Like I basically said...your temps are on the low side. Slowing the flow will raise temps and the humidity will rise also. Slowing the exhaust down will possibly make your humidifier more effective but in an open system humidifiers and dehumidifiers are basically useless during lights on. Once your canopy if filled in and especially later in flower your plants will respirate alot and humidity will definitely increase.

 

[MDT]

After reading your posts, I have a much clearer understanding of how ventilation works now, thank you for your patience and helpful response. I'm just picking this up as I go along and if my understanding of something is wrong, please don't hesitate to correct me.

On to your question.. my room is not sealed, i have air coming in using a 8" inline fan on 24/7.. it just occurred to me, since there is a constant supply of co2 by the inline fan, then it seems the only purpose of the exhaust fan is to dissipate the heat buildup?

 

[Whatever]

then it seems the only purpose of the exhaust fan is to dissipate the heat buildup?

...and to continually supply fresh air, which contains all the CO2 you need, and to remove excess humidity which will build up in a poorly ventilated room regardless of temperatures. You can have temps under control by slowing down the airflow, like you might need to in the winter, but then humidity will rise. One thing I learned about open systems is you want a lot of heat generation because it justifies the need for lots of airflow. The open systems I've built, especially with the split systems I now create, have a temperature variance of approximately 2 degrees F lights on and lights on or off. Heat is your friend...use it to your advantage. It may cost a bit more for the setup but I found it gives you incredible flexibility and provides an optimum enviro when running open. I like to create an enviro that is no different than being outside. I've walked into some rooms and they are stale where it should be fresh and vibrant. You have to kind of forget about humidity though with how I do things.