How to Cool my 4 x 4 grow room


I have my grow room in the attic of my garage , it’s May 6th and the temps are already to hot. I have a 220 cfm fan pulling through the room, internal 5" fan and a 900w LED, the attic is to hot ! Has anyone used a swamp cooler (water evaporation cooling) successfully, there some inexpensive units, but I am not sure of their effectiveness and they humidify which may not be bad, also do not state BTU’s. I found 5000 BTU A/C unit for a $100.00 it will cool a 250SF room, maybe over kill for my 16SF room and they also dehumidify causing another problem. The attic is 12 x 36 with roof above (HOT) and windows at either end, no insulation.


I can’t speak for an attic but I am in a shed and it gets hot with 4 LED and warm days. I am running an AC. I have 4 in intake that thinking of switching to a 6 in. To help pull in more air. 6in exhaust. I cooling two rooms a totally of 48sqft. And definitely need AC to keep temps in check.


@Matt I’m an attic grower myself. You can do it, but it is an investment and a lot of engineering. Here’s what I have. Two tents that have 4" ducting that connects them and a 4" connected to the AC duct that comes in. I have a 240 fan with 6" duct going out. In the air out tent I do have an evaporating cooler. I also have a solar fan that blows air out of attic. Now comes the complexity. I have a smart sensor for temp and rh in both tents. I also have a smart outlet and all fans, lights, and filters are tied to this. I run lights at night and I set alerts when temps get to high so I can turn on the air cooler. Please share ideas back as I had to come up with all this myself and it’s far from perfect.


Thanks for responding Greenlantern,

Is the evaporative cooler for added humidity or cooling? the smart sensors (temp RH) are switching AC unit on and off. How does the evaporative cooler perform as far as cooling? I also have a 240CFM fan on the outlet pipe, with a small fan inside the tent just blowing around. Lights are on timer, outlet fan runs constant. I will also run the lights at night, and a box fan on window on one side of attic room. AC unit looks to be your problem solver. How many BTU is your AC unit? did you build a plenum to adapt to 4" pipe, I understand from reading customer comments the AC unit doesn’t really control temp thermostatically, basically runs all the time, $100.00 dollars what do you want. Thanks for your help,



I turn the air cooler on with my app when the sensor alerts me the temp is over 85. It really only cools it down about 5 degrees, but that’s enough for now. I’m hoping to harvest by end of June and take the summer off. The main AC for the house is in the attic, so I am tapped into the air intake for it. Gives me lots of CO2 and regulated air since the intake is in the bedroom…lots of breathing happening…haha


@Greenlantern has got you covered. Another option in addition to the options above is using a water chiller and a condenser to cool in coming air as well. Welcome to the forum! @Matt


Greenlantern thanks again,
I wish I could cool off the house AC this is a detached garage. I got a late start I was trying to work with 26 year old seeds and 16 year old seeds, not a one popped. after several attempts. So I wasted some time, now we are into some warmer weather here in the mid Atlantic after a cool spring. This is my first grow, I was hoping the evaporative cooler would do the trick. I may design around the small 5000 BTU window unit with make up air as so I don’t over cool. Depends how well the units thermostat controls operation and temp.


Covertgrower thanks for replying,
What type of water chiller are you speaking of, I am very interested in the chiller option. Heat under the roof is extreme and I just don’t have a feel for cooling capacity based on the limited sales information given for these products.


Thanks Smokin_ernie for replying,
AC unit is my thought as well, from customer feedback on the 5000 BTU AC unit I was thinking of purchasing they say the unit basically runs all the time (thermostatic control doesn’t work very well). That would over cool the 4 x 4 grow room and dry it out, I was thinking not to try cooling the entire attic just the room it self. I am assuming you are cooling the entire shed.


@Smokin_ernie @Greenlantern didn’t want you miss your messages. ^^^
When responding be sure to use the @ symbol. Like @Covertgrower so your response isn’t missed.
Here’s the water chiller I have in my wish list. I’m not sure what size you need, and I’m not sure what your budget is, or handy you are. They have multiple different sizes, and commercial units if you want one. You’ll need to purchase heat exchangers also, but those come in a variety of sizes. This air can be just recycled inside the tent, so you’re not losing all of your cooled air. The chiller could even be located on the first floor if that’s an option. Behind something to disguise it if need be.
Active Aqua Chiller, 1/4 HP


Cooling only half of the shed. So what I have is a room that is 6x6 that the AC is in and plugged in to a temperature controller. That is set for 70f. The grow room is 6x4 and it pulls it fresh air from the AC room. So far it has been running well on a 90f day the grow room was at 85 with the lights on.

Thanks @Covertgrower for the tag.


Anytime @smokin_ernie all out of likes.


@Matt @Covertgrower I would scrap the bag seed and get some quality ilgm. Start with autos to learn and pay attention to the different height for certain strains. I grow compact or average height since I only have 5" vertical space. I also noticed autos pop faster and you could get the job done in 3 months if conditions are right. Best to do fall and spring if u cannot regulate temps well. Get everything set up this summer and do some temp/rh tests to make sure your system is working. You could germinate in August and then grow fall.