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Need assistance battling temperatures in my 4x8 grow tent and negative pressure


Active Member
I have a 4x8x7 Grow tent set up in my unfinished basement.

Currently my setup is:

- On the left side of the tent I have a medium size humidifier and i just purchased a 12000 BTU standing air conditioner to try and cool down the temperature spikes. This takes up one foot of the 8 foot wide tent
- I have two 12 inch oscillating fans- one on each end of the tent
- two 600 watt hps/mh bulbs- one light has a air cooled tube hood reflector and the other is just a hood reflector
- 6 inch Hurricane inline fan on low currenltly

My goal is a constant 77 Degrees and 60-70% Humidity in Veg ( I am open to hear better temp and humidity numbers) and my basement ranges from 75 at night and can spike to 87 degrees.

7 Gallon Smart Pots- 70/30 Coco/Perlite
Drain to waste with drip irrigation

ROW 1 IN TENT- a/c BM BM BM BM Air Conditioner and 4 Blue Mystic Plants in week three of veg
ROW 2 IN TENT - humidifier KU KU BM BM Humidifier and 2 Cali Kush and 2 Blue Mystic Plants in week three veg

My Question.

Once I put the new air conditioner inside the tent (with the exhaust fan dumping into basement) I get huge negative pressure and the sides of my tent bow way inward.- i mean way inward- cracked one of the supporting rods cause of the negative pressure. The oscillating fans are getting stuck as well and will not oscillate when I zip the tent closed.

How can I use this air conditioner most efficiently? Should I vent it to the outside through a window (it's 90-95 degrees outside) ?Should I open vents in my tent to let more air from the basement into the tent? If I do this, won't I just be cooling the whole basement?

How can I fix the air flow so that the oscillating fans will oscillate when I close up the tent?

Is my setup all wrong and should I be doing something totally different? Does anyone have the almost perfect setup for a 4x8x7 that they use to just grow for their own needs?

Thank You

Chris Scorpio

New Member
The AC pumps a lot of hot air in the room
I'd move it outside the tent, vent outside

How big is the basement room? Will the AC cool it? If not then pump that air into the tent
Ya may try turning down your HPS lights if yer ballast is adjustable

I'd also get a cooled hood for the second one if possible

I ran my 600w HPS in a 4x4 last summer. Temps always 86-92 deg and I had no issues. This year my QB lights max I get is 84deg


Active Member
Thnx Scorpio,

I moved the air conditioner outside the tent and it's blowing the cold air into the tent now. I used a cardboard box and taped it to the outgoing air and then attached it to one of the holes in the tent. The issue I have now is the sensor on the a/c is outside the tent and it sent the temperature of the tent way down to 65 degrees. I had to open a few few of the vents on the tent so the temperature in the tent went up to 77 degrees.

Is the only way this will work is to cool the whole basement which is 40'x20'. If I have to cool the whole basement down to 77 degrees, should I still have the cool air entering into the tent or just have the it outside the tent just cooling the whole room?

Is there any advantage to having the cool air route through the tent, past the plants and then out one of the vents, into the room, rather than having the a/c just cool the entire room while the air conditioner sits Outside the tent?


Active Member
The easiest route will be to cool the entire area so you don’t get so much negative air pressure inside the tent. You’ll still need to vent the hot air from the tent outdoors and allow cooler air to flow in through vent ports.

It’ll cost a little more to cool the entire area but you’ll have much more stable temps and it won’t make the ac unit cycle on and off so quickly as the internal temp changes.


New Member
Ok heres what I did
Purchase a portable A/C with remote control
Purchase Sensibo Wifi AC remote

The Sensibo remote sensor allows you to put the sensor into the tent and control the Ac from your phone, set schedules and alerts. It also gives you 24hr graphs of humidity and temps.

I had to tape the sensor to my tent window since it is an IR remote and needs a line of sight to the AC. but see how I did this in pic #2

The AC you need to build a box out of cardboard and tape it up with AC duct tape put it over the vents of the AC unit and pump direct to the tent from outside like I did in pic #1

See the sensbo App pics 4 - 5 and 6 it is accessible on phone app and desktop app..
All kinds of customization and calibration options.

Check on everything and control it all from your phone no matter where you are



You can see the sensor/remote in the middle of the top of the window


Daily Graphs with realtime stats

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