2x4x5 tent still running hot with 180 cfm exhaust?

Setting up a 2x4x5 grow tent with a 600w LED, 300w led (true watts is about 400 between both lights), carbon scrubber, a 4 inch 180 cfm in-line exhaust fan, and two small clip fans. The tent is located in a closet and has HVAC running out of the room into a vent in a hallway. There’s nothing too major in terms of turns in the ductwork, just one where it goes up out of the tent from the fan.

I haven’t started growing yet but the problem seems to be heat. The tent is in a closed closet with a door that has a natural temp of about 74-76. Problem is when I turn the lights/fans on the temp in the tent gets up to 87-90 degrees, even if I take the 300w light out.

I have both the intake vents open as well as the carbon scrubber/ exhaust mounted at the top of the tent. I also have two clip fans circulating air/pulling air in from the intake vent.

Could it be the closet itself isn’t getting enough cool air into it? There’s no vent into the closet besides the hole I put into the wall to run exhaust, which is sealed besides where the duct runs.

Site won’t let me post links to the exact lights/fans I have but I can provide more info if that helps as well.


Thanks in advance for any help!

I allegedly grow in a 42"x42" 7 ' area. I used a different cob coolhood setup. I run ~700 w allegedly with a 85 degree max 14" below a cob. Intake 75. 4" fan at around 100 cfm probably. I use a speed controller for the fan. I started with blurples 5 years ago and they worked. 4 ~200 w actual in the area. I had to leave it open and Max my blower at ~180 cfm. Still got to hot. Nineties and lots of issues. After hanging on here and learning about diy with cxb3590's I took 2 10" wide by 40" long heatsink. I have 2 connected into a 4 inch Y that I put a sail switch in so if I don't have enough air flow my lights shut off. Anyway I use a 6" phresh inline carbon filter. Allegedly. 4 " blower sucking through it all. The point of my story is I have tried certain other designs such as a ~300 led 561 board with heatsinjs and a cool good design like I have used for over 3 years now with success in keeping the area's heat issues under control even at 850 watts I'm below 90. I run ~650. It seems a lot of radiant heat comes off the front of some lights such as the multi led blurples. Plus efficiency is less. But I have also been unable to cool the area with low air flow using 561 series diode boards. I have 8 boards that are going up on fleabay when I get time. It seems for me the best I have found for my stealth has been cobs with a big heart sink then seal the back if the sink and suck air through it. Less plant facing radiant heat for me. I hand 2 thermometers as well as use an it gun on leaves buds etc. To check and compare different LED lights. I need low flow for quiet as it's stealth. I can provide pics if you like. I jumped many light bandwagons the last 3 years. I'm back where I started. 16 cxb3590's in the area. And out well over$1000 in different led boards. ymmv

Ladengin said:

Could it be the closet itself isn’t getting enough cool air into it? There’s no vent into the closet besides the hole I put into the wall to run exhaust, which is sealed besides where the duct runs.




Thanks in advance for any help!

Click to expand...

Yes it could be.
The extractor fan can only take out what it can pull in to a degree. It will create negative pressure but without been able to freely bring as much air in passively to replace it as needed it will just be overworked and add to the heat.

Also where are you taking temp readings?

coreywebster said:

Yes it could be.
The extractor fan can only take out what it can pull in to a degree. It will create negative pressure but without been able to freely bring as much air in passively to replace it as needed it will just be overworked and add to the heat.

Also where are you taking temp readings?

Click to expand...

I tried leaving the closet door open last night while running but the temps still went high.

I have two thermometers laying on the floor of the tent.

Ladengin said:

I tried leaving the closet door open last night while running but the temps still went high.

I have two thermometers laying on the floor of the tent.

Click to expand...

Ok first you need to know more about taking air temp correctly.
You do not want the thermometer in direct light. It should be above the light line out of direct light. Otherwise your picking up the radiant heat from the light, plants can take far more radiant heat than they can high air temps.
Its the air temp that is important.

If temps r getting high when light is on, then we know it’s the light.
Option 1, sell it get a air cooled hood! Intake/exhaust Ventilate the hood from outside the tent/closet.
Option 2, add the intake fan as well, go bigger fans.
I run that same size tent for my mothers/clones in veg. Mine is sitting in a open room right under my mini split unit. I use (1) 8” in-line booster fan for my exhaust, and (1) 6” in-line booster fan for my intake. I only have (1) 4’ t5 4 lamp in there for my light.

I need to see it. Can you post some pics?

Purples get hot as fuck

coreywebster said:

Ok first you need to know more about taking air temp correctly.
You do not want the thermometer in direct light. It should be above the light line out of direct light. Otherwise your picking up the radiant heat from the light, plants can take far more radiant heat than they can high air temps.
Its the air temp that is important.

Click to expand...

Makes sense. I moved the thermometer under a piece of cardboard and am getting temps of 84-85 range. Better but still a little on the warm side. I’ll try to take some pictures today and post them.

you also want your thermometer to be at canopy level. those are the temps that matter, the temp on the top of your pot is less than useful

How much space is in the closet? The only time I've had luck controlling temps in small spaces like that, are in insulated (wood) cabinets. Ran intake vents under the cabinet (had feet) and exhausted over the top and out the open door. I could NEVER close the door, except for emergency situations (unexpected visitors etc.). I always had to be pulling Conditioned air from the floor of the main room the closet was located in (during the summer). When I tried my tent in the same closet, I got the same results as you. The whole closet would heat up unbelievably. The less space you give the tents to breath, the warmer they get. My 2x4 Gorilla is in our A/C'd bedroom now, about a foot from the wall on either side and temps are perfect with my 167 watt COB. In the winter, the lights seem to help offset my gas furnace and reduce my bill.

i grow in a 2x3x5 tent inside a closet. my inline fan i use for exhausting is 435 cfm. i use a 400 watt hps cool tube and keep it about 14 inches away when tent is closed. temps stay around 77-80 degrees. i think your problem is your venting all that hot air straight into your return for air conditioning. instead of the a/c keeping your house cool its has to cool all that extra heat your injecting into it first. i advise you exhaust outside. this is what i do. until your ambient temp drops you will struggle to keep the temp under control. if you cant vent outiside another option is you could add a/c unit to the room the grow is in and keep the door closed too keep out the hotter air built up in house. upgrading your inline fan would be a big help too. like i said i use 435 cfm for a smaller space