How powerful does a humidifier have to be for my grow room?

I built a plastic 3’x3’x5’ grow room. I have a 190CFM inline fan at the bottom and a 230CFM exhaust fan at the top.

It’s very dry where I am. I went to Walmart and got a .3 gallon humidifier that claims to be able to handle 219 sq foot room.

I turned both fans on and put the humidifier in the corner and after 30 minutes the humidity had not changed at all. It actually slightly decreased, due to the fans running. It was between 28% and 40%.

Should I wait for longer than 30 minutes or is this humidifier just way too small?

The fans are obviously circulating air quicker than the humidifier can.

There is a 1 gallon humidifier at Walmart that claims to work for a room 500sq feet and is advertised as being for medium to large rooms


And I also see misting/fogger units online for a bit more money, and I’d have to wait for shipping

The mist maker says its 500ml/hour and I see some cheaper ones on eBay at 400ml/hr.

Do you think the 1 gallon one from Walmart would suffice?

Do you think my fans are too powerful for this space?

:potted_plant::purple_heart:

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Can you slow your fans down any? :green_heart::metal:t2:

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What is normal rh for your area? Mine is low. My solution has been lungroom control. When i need a bump i turn off exhaust and just keep circulating fan. 20% humidity bump about. 40%and above will grow. A little slower veg but doable totally. Gl and I suggest dont fall down the money rabbit hole and not get results. 3x3 is pretty easy to regulate actually.

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@StonedCold13 I was thinking about slowing them down with a dimmer switch I have handy but don’t know if that would be safe for these fans or not

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I wouldn’t do that, i was told a couple years ago some fans can’t handle that :person_shrugging:t2:
Do like @Storm suggest and raise your lung room rh.
Maybe try put your exhaust fan on a timer :green_heart::metal:t2:

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I use this on some old inline exhaust fans. On the fan you have in the bottom port, is that exhausting or bringing in fresh air from the lung room? :love_you_gesture:

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@OGIncognito the fan at the bottom is bringing air in and the fan at the top is pusbing air out.

I actually don’t have a lung room yet. I’m new to all of this and this is actually the first time I’m hearing of it.

My understanding is that it’s basically temperature and humidity controlled room that the inline fan sucks air out of and into the grow room?

How big would this lungroom have to be for a 3’x3’x5’ and how can I go about building it? Smaller is better for me.

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The lung room can be any size that’s comfortable for you you to navigate. My garage was my lung room for several years and I fought the environmental conditions daily. I now have a 9 x 15 grow room that I condition, I also bring in air at the bottom and exhaust out the top. For seedlings it’s best to try and keep that area small (tent) , it’s easier to keep the RH and temps high with a single humidifier pumping into or in the tent. An even easier solution for the seedling period is just take a clear solo cup and mist the inside and place it over the seedling, removing daily to re-mist and allow it to get some fresh air. Water a few ounces every 3-4 days. Remove the dome completely when the leaves are touching the side of the dome :love_you_gesture:

Dome method

Humidifier method

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I don’t really have anything I can use as a lung room. I feel stupid for not thinking about humidity until this far into the build.

I read that your fans should be circulating the entire volume of the tent every minute. So if my tent is 3’x3’x5’ that’s a volume of 45 cubic feet; meaning that I’d really only need 45CFM fans?

My fans are 190CFM intake and 230CFM exhaust. So they would be circulating the entire volume of the tent 4 or 5 times in a minute.

So could I set the fans to run for 15 seconds on, and 45-60 seconds off using a short interval timer? This way the fans would circulate the entire volume of air within 15 seconds, then wait a minute, and circulate again. Maybe this would give the humidifier time to keep up pace?

Does that sound like it might work or am I way off on my calculations?

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I also had an idea in my mind of a 5 gallon bucket with a humidifier inside and ducting from the lid of the bucket leading into my intake fan… But the bucket would probably be too small right?

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I wouldn’t go too far down this rabbit hole. As long as the fan is capable of exhausting the hot air and the grow space is capable of maintaining temps below 85 you’ll be ok. My fans run continuously to maintain the tent environmental conditions as close as possible to optimum but within the different grow stage ranges.
Seedlings- temps at 76-85 RH 65-75% fans can run on low for this stage.
3 week after sprout and early veg same temps but lower the RH down to 65%.
Later veg temps the same and rH 55-65%
Flower temps 65-82 with RH around 45-55%. Without a controlled environment it’s a daily check and I use simple temp/RH devices and adjust fan speeds and temps by hand with a humidifier or dehumidifier and temps with a portable heater or AC depending on the time of year :love_you_gesture:

@OGIncognito Since my fans only have one speed, do you think running them in intervals like 30 seconds on and 30 seconds off would achieve the same effect as slowing the fans?

My main goal right now is to run the fans as little as possible in order to allow the humidifier to increase humidity. Humidity is very low right now.

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You could turn that lower fan around to exhaust the tent, place it a few inches away from the opening. This will lower the volume of air being exhausted and allow the humidity to work a little better. Trial and error Grow Bro under your conditions. I’ve been there and grew in a garage for 3 years :love_you_gesture:

Thanks for the advice. It’s getting to be a real headache. The humidifier can easily bring the room to 70% humidity but as soon as I turn on the fans it’s dropping back all the way to 28%. The only solution I’m seeing is less powerful fans, but if I could work with the ones I have that would save money

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After buying a fan speed controller locally and running my fans at the slowest speed possible, the humidity was still far too low (maybe 30%) even when running the humidifier.

My new plan is to replace the inline fan at the bottom with the actual humidifier. I’m connecting ducting from the exhaust of the humidifier and leading it into the tent. Then I’ll take the 190cfm fan and use that as exhaust at the top, but at it’s slowest speed with the controller. I’ll post photos tomorrow with the final results.

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Your plan is good. The humidifier will be more effective if you put it inside the grow room, though. Is there a reason it must be outside?

@Venturi The humidifier’s exhaust is easy to attach a duct to and lead the duct into the tent. The design of the humidifier doesn’t allow me to attach a duct that will SUCK air into the tent. The idea is that the humidifier’s fan is solely responsible for pushing air into the tent.
I also have another small humidifier inside the room. I haven’t tested the new setup yet

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I didn’t realize you bought another humidifier.

No fan can push air into a tent faster than the exhaust fan removes it. Airflow through your tent will be 190 CFM (once you make it your exhaust fan) regardless, unless you do something that restricts intake. For example, if the humidifier is the sole air source and its fan’s CFM is less than 190, it will create a restriction that places an unnecessary load on the exhaust fan.

Ducting a humidifier’s output into a tent can be tricky because any bend greater than 90° from vertical will cause condensation to drip onto your tent’s floor. If you avoid that problem by angling the ductwork properly, the moist air may enter well above the plants and be sucked out the exhaust without changing the humidity the plants see.

Im assuming the measurements have been in an empty soace with no plants
If so keep in mind that the humidity levels will be higher with plants in it

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@Smokesdaily that is a good point!

@Venturi I bought a fan speed controller for the 190CFM and have it running as slow as possible. Even with the exhaust being slowed as much as possible with the controller, and the humidifier acting as the intake fan, I’m only achieving 50% humidity. And that’s with the .3 gal humidifier also inside the tent.

There’s room to improve the ducting, I just set this up to test it

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