Hot Topics: Hack Your Window Air Conditioner

A small air conditioner in the window of a brick apartment building.

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This is a common problem. You have a window air conditioner in just one room, and need to cool a whole apartment. The room with the A/C has to be set cold enough to see your breath, just to chill the other rooms to moderately comfortable. What do you do? The Forum has the answer, complete with diagrams. And even if the original poster is too cool to listen, you can at least benefit from his asking the question.

Original Post: Simple duct for A/C

Revrant Member

I'm trying to greatly reduce my electrical bill by attaching a simple duct to a "wall (window style)" air conditioner in my apartment. As is, I have to turn 80 percent of the apartment into an icebox to have a warm bedroom, because excellent apartment design. So I want to attach something to the front of the unit and direct it with a duct to the bedroom alone, but I have no understanding of the terminology and thus no idea what I'm looking for beyond a simple duct.

What would someone suggest I do to accomplish my circulation goal cheaply and efficiently?

Highlights from the Thread

SJ-JT Member

Can’t speak to "ducting," but this is what I did in a similar situation: two fans, medium size. Essential that they have a low speed setting. You don't want turbulence; you want to coax the hot air in your bedroom out, and coax the cold air from the iceberg room in. The "mix" occurs in your bedroom all on its own. Turbulence will just bounce the air around and not exchange it between your bedroom and the iceberg.

Place one fan high, sucking air from the bedroom and sending it toward the AC. The other low, drawing it from the cold floor and sending it toward the bedroom low - as it warms inside the bedroom it will rise toward the ceiling. Don't place the fans vertically lined up with each other. Don't place either inside your bedroom, but near the entrance. Exact placement is trial and error. Creating the air exchange will be affected by furniture, walls or whatever may be in the way. Walls can be used to reflect the air (either cool or warm) toward where you want it to go, like bumpers on a pool table. Eventually the iceberg room and your bedroom will have more equal temps.

PJmax Forum Topic Moderator

My sister has a similar issue only her AC is in the bedroom and it used to freeze the bedroom to cool off the living room and kitchen.

I bought her a small floor fan and she has at the entrance to her bedroom. The AC airstream is directed up and when it comes down its right at the fan. The fan is pointed up thru the next room. Sort of a leapfrog effect. Since cold air falls, if you point the airstream up it will pass thru the room without overcooling it.

Fan placement for A/C extension.

A duct system would look pretty out of place, not to mention cumbersome.

Revrant Member

Okay, neither of those answers my question or is helpful at all, anyone else?

Andrew Member

Most room and wall air conditioners are not designed to have external ductwork attached to them. The fans do not have the necessary power to overcome the increased static pressure caused by the duct. You were given two very good ideas by PJmax and SJ-JT to help you achieve your goal, and I agree that those are your best solutions.

Revrant Member

That's why duct tape exists, champ, the do-it-all miracle adhesive, and it appears we have invented fans inside ducts for that very purpose, imagine that! No, putting fans in the room is not a good solution, it is a very poor idea that accomplishes precisely nothing, because I had already done that and guess what? The air went where it wanted to, which was all over the room. That's because it's air.

Now if no one has any real replies, then please don't reply, "put a fan in front of it" is not an answer. If I wanted that answer I'd ask the bearded 19-year-old at Menards.

Furd Member

Putting a fan in front of the window A/C CAN in some instances work quite well. Obviously it doesn't in YOUR situation but that is no reason for you to get snippy about the FREE advice being offered.

Every "window banger" I have ever seen has the discharge grille above the intake grille. Since cooler air is more dense it has a tendency to fall as soon as discharged and then is sucked right back into the intake. This alone causes a window unit to not perform all that well. Anything that you can do to prevent this short circuiting will help.

Andrew is correct that the blowers in window units are not powerful enough to move much air through any attached ductwork but you MAY be able to move some air through an attached duct and using an in-line duct booster fan MAY help. You didn't mention how far away the hot room is from the A/C unit but MAYBE adding a piece of flexible duct will help. It may help to add it to the discharge or it may help to add it to the intake to "suck" the hot air from the far room, there is no way to predict and you will just need to try it. The downside is that you need large ducts to reduce the resistance to the air flow and that will make quite an obstacle on the floor.

Revrant Member

Going to completely ignore the fan part, again, because I am standing in front of a stoned Menards employee at this moment.

I have basically the information I asked for, and so many replies in I finally get to say thank you.

Furd Member

Please let us know what you did and how well it worked.

tomf63 Member

It amazes me at how some people react to a well thought out suggestion for a cure to a problem that they are having. Even backed by some facts from pro's regarding how the unit in question worked and reasons not to do it, that person went on and did exactly what they felt like doing.

So why was the question even asked? The answers and further helpful ideas weren't going to change the op's already though out cure for the problem. These are DIY "Help" forums, aren't they?

Furd Member

I offer advice based upon my training and experiences. I have no control over how, or if, anyone applies this advice. It IS irritating when a person ignores my advice but I manage to cope.

Andrew Member


I have seen this situation so many times I can't count. Like Furd, I have quite a bit of practical experience dealing with this stuff. When my advice is ignored, I just let it go... :-)


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