How do you install a window air conditioner in the top of a double hung window

Installing a window air conditioner in a double-hung window is an easy job that should take less than an hour in most situations. The steps given here are meant to serve as a general guide.

Various brands of window air conditioners have differing attachment methods. New window air conditioners are packaged with manufacturer’s instructions for installation—be sure to follow these directions. If you attach a unit improperly, it could fall.

Measure the size of the opening to make sure the unit will fit. See Sizing a Room Air Conditioner for information about sizing the unit.

The best type of window for receiving a window air conditioner is a double-hung window that can be opened at the bottom. The AC unit will need to be plugged into an electrical outlet that can supply the necessary current without overloading the circuit.

1 Completely open the bottom sash of the window, remove the window screen if there is one, and clean the sill and channels with a vacuum.

2 Prepare the extensions. Most AC units have accordion or sliding extensions that slide to completely fill the opening. Some units have these already attached; with other models, you’ll need to slide them into channels on the side of the air conditioner. It’s best to prepare these before putting the AC unit in the window opening.

3 Prepare mounting brackets. Some AC units simply sit on the windowsill; others rest on special brackets that attach to the sill. If you unit utilizes mounting brackets, install these brackets according to the manufacturer’s instructions. Be sure to level the unit according to the recommendations (typically with a slight downward slope toward the outdoors to allow for drainage of condensation).

Make sure the fasteners are secure. Some units come with two lengths of weatherstripping foam—one goes along the sill beneath the unit, which you can put in place now. The other will go on top of the unit once it is installed.

Maxwell left teaching in 2001 to start Apartment Therapy as a design business helping people to make their homes more beautiful, organized AND healthy. The website started up in 2004 with the help of his brother, Oliver. Since then he has grown ApartmentTherapy.com, added TheKitchn.com, our home cooking site, and has authored four books on design. He now lives with his daughter in a lovely apartment in Brooklyn.

published Apr 11, 2007

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Hello AT,

My AC units are currently installed in the bottom of my windows. I’ve
heard it’s possible to install units at the top of the window instead. I’d love to do this and say goodbye to cold air blowing directly on me and hello to unobstructed views…

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Anyone out there have guidance about making this transition safely (I surely don’t want my units falling out of windows)? I’d really like to find someone to hire to do the installations for me. A friend also
mentioned there might be some regulations about this of which I need to be aware.

FYI: my windows have metal frames.

Thanks for your help, Dawn

Dear Dawn,

While we haven’t done it personally, we’ve had many clients and friends who have. Most of them have hired help, but you can totally do it yourself if you are handy and have help with the lifting, etc.

The main thing is that the unit has to be attached to your window frames (screws), which is a little trickier with metal frames, but definitely doable. Metal screws will go into metal.

Also the window below has to be propped to stay snug up against the machine. It can be screwed into place itself or propped from the outside.

If you call an AC installer, we estimate that the cost would be around $200.

The thing we DON’T have any idea about is the regulations for your building. Does anyone know the rules around this?

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