420 Magazine Background

Duct Work From An AC Window Unit

Thread starter #1
Room is 11'X14' with 1 each 4x8 and 5x10 tents. I see no reason to use the window AC to cool the entire room and want to use for the tents only.

Any one know of a good way to do this?

Only thing I can think of right now is to attach a 40 gallon tub over the face of it and attach a couple duct flanges to it to directly connect the the ducting hose to the tents.

I don't want to re-invent the wheel here if someone already has a good way to do this .... please let me know.



New Member
you hit it on the head. Just fit the container snugly on window unit, and use weather stripping to plug up any air leaks. You can also use the spray foam if you want it to be a bit more permanent. Use a starting collar for each new port.
I would also highly recommend a pre-filter in that box so capture excess dirt and moisture that could cause issues for your girls! (this also preserves your carbon filter longer)


New Member
No problem! If it all works out well for you, you should post a how to on the set up.
You can also route your CO2/dryice into that central box and have it distributed for you.


420 Member
This method probably won't work.
Air conditioners have a thermostat mounted on the cooling coils. By sealing a tub over the front of the unit, you are creating a large space for the unit to cool, which is almost like sealing in the cold air, which will cool the sensor faster, and shut off the unit before proper cooling is achieved. The unit will also just draw this cooled air back in before it is even pushed through the ducting.

You also want your ducting to be as short as possible. The blower on an AC unit is designed only to blow air into the room, not through duct work. You may also need to use a booster fan on the outlet ducting.

To make this work, you want 2 separate housings on the AC unit. One must draw air from the tents, and the other must direct cool air to the tents.


New Member
You're completely right Antics, although i feel using a custom made/fitted duct would solve the problem.
So basically, we'd either make one from scratch using a small piece of sheet metal, or find and modify something that'll work =p
1. insert that duct into the output of the Window unit
2. insert the other end into the nice little duct box.
3.Connect each duct to the duct box.
4. run the ducts to the tents.
5. leave the tents exhausting their heat into the room. (as the hot air moves over the cooling coils and keeps the ac running all sexy like)

Ive skipped a few things, but thats because im gonna make a little drawing for you guys and post it here.
Thread starter #8
Ahhhh crap - Never had a window unit and did not realize that the bottom front part of the AC was intake! I stupidly assumed it was from the ass end outside!


Your diagram looks sound. Issue I have is living in Central America and not easily laying hands on parts :) .......

Also - My original plan was to vent the tent exhaust straight outside after the scrubbers. I was also going to put in an 8 inch "passive" intake into the room that would draw in fresh air as required from equalized pressure....... Tents would also have 4 inch passive intakes that would work the same when the AC was not running. I plan to run the AC during the day for only the hottest 7 hours for the sleepy time temp drops and run the light at night due to it being cooler and a HUGE price drop in energy costs per KW.

Hhehehhe I am going to have to let this bake in my brain a bit more and ferment :)

But thanks to you both in setting me straight!


420 Member
Sorry for peeing on the parade man, I'd just hate to see you go through all the work and find out it doesn't work as it should :(

Wizgrow, are you buying a new AC unit? If yes, if you buy what is called a portable air conditioner, that will have most of the parts you need. They stand in the room (easy to vent into the tent) and it comes with ducting to vent the hot air outside through a window.


New Member
The portable A/C units are pretty handy, I use one to cool my studio. You'll definitely want to put an inline fan booster to push that cold air through both tents. They get pretty chilly pretty quick, some like mine come with several settings for fan, energy saving, and dry air conditioning. (plus thermostat and remote of course)
If you're trying to do something a little more lowkey/diy, you could create your own swamp cooler, or icepack fan/cooler poorman rigs for pretty cheap, and easy to come by materials. Using gatorade bottles filled with coolant, or ice packs, you can recycle them again and again for constant temps by throwing em' in the freezer.
Thread starter #11
The AC unit was donated for the project by my partner. TBH the unit would probably be fine doing the whole room and may end up being used in that capacity still. The Flower room just happens to have some pretty serious vaulted ceilings...........

But I may end up putting the unit in the Veg room which is about 8x8 and only 7 feet high. I was thinking it would not be needed but it might.......

Then I would/can order one of those portable AC that costs $300+ but actually do what I am looking for much easier in the Flower room.

Problem for me is that getting equipment down to me takes 3 weeks + so I am really trying to cover all my bases BEFORE I run into issues. LOL - That and the fact that my startup capital is basically GONE! But I did get some NICE intelligent Gro lights which are real fun to play with so far.....

Thanks guys for the help.......... "I'll get er done" :)
Thread starter #12

In your schematic/PIC where are you finding rectangular duct cover that would fit over the AC unit? Having a hard locating one on line.......

So ya, deciding to go the route you kind of laid out...... I just got done looking @ the portable AC units and frankly...... unimpressed. For (1) I really don't have the free space for it and (2) they seem be a lot more inefficient than the window units...........


New Member
google or amazon transition duct. they'll be right there ^.^
and yeah, against a proper window unit, the portable A/C is a chump. But if you literally just needed something lower key to put in a crawlspace, or attic grow to keep one or two tents cool they are pretty nifty.
You can also find 20-24$ inline 240cfm booster fans on amazon too for that duct box.

Can't wait to see how everything works out for you man.
Thread starter #14
Transition was the word i was looking for thanks

I seriously doubt a an intake booster fan will be needed as the negative pressure should do the trick. I will diagram it out later today since stabilizing pressure and passive intakes will play a major role but also make it kind of confusing.....


New Member
The inline fans were more or a less a precaution on my part in design. If you've worked out a good system using negative and equalizing it across tents, then that's excellent, and cheaper =p
Looking forward to the end result, hopefully we'll get pics?


Well-Known Member
A bit of an old thread... but I just had some experience in this area and found a solution that works using a window ac unit.
Due to circumstances beyond my control, my grow room is an outdoor tin shed with no shade on it. It's an oven. Without cooling, the temps are in the 120s naturally. With ac cooling the shed with insulation installed, it was very hard to keep it under 100 with the lights running. I tried many things, but in the end was really unable to solve the problem.
I had a tent I was using for veg inside the shed. I simply took the tent and moved it to the wall the AC was on. I opened the door on it and put the door opening over the part of the AC unit extending into the shed.
Now, I do have to actually rotate the tent a bit to get to the plants, but the temps have stayed right around 80. The AC unit itself is working about 1/10th as hard as it was.
I'm really loving this configuration. I haven't had a chance to crank up the 400W HID CoolTube, but I think it can handle it pretty easily.