Mounting a Standard Air Conditioner in a Sliding Window (From the Inside, Without a Bracket)

Many people have inexpensive air conditioners that are intended to fit into a double-hung (vertically sliding sash) windows and want to use them in horizontally sliding windows. If you already have some of these air conditioners or are attracted to them because their price tags are significantly lower than that of casement units, portable units, or central air, it is possible to make a frame to adapt them to sliding windows.

These solid, simple frames require no exterior brace.  This is perfect for apartment dwellers and those who only need an air conditioner a few months of the year.  It takes about an hour and some basic lumber and tools to construct these frames.  Once built, your air conditioner can be installed and uninstalled in minutes.  (Please note that window air conditioning units aren't intended to be permanently installed.  These frames also make it simpler to remove them at the end of the warm season.)

The units pictured include unfinished plywood.  However, this can be finished, painted or replaced with plexiglass or other materials, as the sheet lumber simply covers an opening and is not structural.

YOU NEED:
2X4s *(2 or less but the amount varies)
12 deck screws (or other long wood screws)
Drill
Saw
Screwdriver
Plywood Scrap

• These window sills in the picture are fairly deep, allowing for the use of 2X4s. You may be able to substitute other lumber for shallower sills.

Step 1 Take Measurements

Measure the width of your air conditioner. Be sure to include any vents that stick out on the side in this measurement. (My first attempt to build this did not account for the vents and the air conditioner couldn't slide in. I considered building the frame around it but it was simply too awkward to maneuver this frame + air conditioner into place.)

Measure the height of your air conditioner. This height should be the box height and not include the lips on the bottom or the top.

Measure the height of the window opening. Take this measurement right up against the window because it will give the shortest height of this opening. (Again, mistakes reminded me that sills can angle away from the window, giving a height that is too long.)

Comments

[Tinker Tom]

Great instructable. I moved into a highrise last year with side sliders and wasn't sure how I was going to mount an AC.

I picked up the materials at my Local Home Depot and had the cuts made there as well. The only tools required were a drill to pre-drill the holes and a screwdriver. The entire project cost about $70, $45 of which went toward two sheets of plexiglass and mini blinds. The second sheet of plexi diverts drips from above.

Thanks for the great idea.

Photos attached.

[starshipminivan]

What a beautiful thing! $45 for such a nice finished product is great! I love the miniblinds and curtains.

[Tinker Tom]

Thanks. I have a southern exposure so the blinds and curtains help block the midday sun.

[seaweed009]

Hi, My window space is 17 3/8. Do you have any suggestions for me? I am desperate. It is very hot this week and Friday will be 101, maybe higher too due to humidity. I am going to buy a 5000 btu unit and am hoping to somehow get this in this space. There is not enough space to frame it. I could place a wood frame above the unit but how to hold the unit to this frame is the question. Plywood would of course cover the frame.

starshipminivan do you have any suggestions? Thanks for your help or anyone else who has any ideas.

[starshipminivan]

Oh dear, I see that I did not respond to this comment when it was originally posted. I hope you found some relief. In that situation, where width is tight, I'd simply build a bracket to mount to the house which would support the unit, if possible.

[jenga-kun]

How do you screw together the 2x4's when they are perpendicular to each other?

[starshipminivan]

You screw through the outside piece (the vertical ones as shown in the picture) into the horizontal piece. Deck screws, which I probably should have pointed out by giving their dimensions, are very long and sturdy and should have no problem securing the two pieces in this way.

[jenga-kun]

What I meant was how do you hold the wood together to screw them? Screwing together two 2x4's when they are perpendicular to each other is kinda hard. Do you put them in a vice? Do you glue them beforehand then screw them? Do you get other people to hold the wood while you screw them?

Also do you have to drill pilot holes beforehand?

[starshipminivan]

I can see my reply is coming very, very late. I used my husband to hold it together but 90 degree angle clamps are extremely helpful here. I did drill pilot holes.

[stubbsonic]

I just finished this project. Thanks for the instructions.

It was a little more challenging because I only had warped 2x4's. Perhaps I got lucky because everything fit ok. Needed a little tweaking here & there.

My cross-piece in the center had to stick out a little toward the front to accommodate the A.C. unit. Stapling the screen to the back worked fine. I worked with some bracket steel and made little holders that the cover board slid into on the bottom, and fashioned some twist latches on the top corners to make installing and removing the board easier.

Thanks again. It is SO hot. The swamp cooler just doesn't work anymore. Now our bedroom is our little oasis.

[jsanchez17]

This may be a silly question but can I just use plastic to fill in the extra room around my air conditioner hose? I have a standing unit and a side ways opening window, so instead of using wood to fill in the top I just used a big sheet of plastic, will this work?

[starshipminivan]

For my portable air conditioner--the kind with the hose--I have a piece of plexiglass that's made to fit my window opening with the hole for the hose. So, yes. The plexi was cut and framed to replace the window screen during the summer months. It was done at the local glass shop. Since most of my windows have the same size screen, it can be moved around between each of the windows.

[debbiedoo]

Thank you again for the diagram confirming installation. : )

[marquisk2]

Will something like this work if the window only opens roughly 15 inches? I don't think I can find a a/c that's small enough!

[starshipminivan]

I don't think it would simply because, you're right, the standard air conditioners are larger than this, even the tiny little 5,000BTU units are something like 16" wide. The 2x4 frame actually narrows the width of the window opening (depending on the window framing itself) but you could probably build a metal frame that would not narrow down the opening of the window any more. However, the size of the air conditioners are still the problem here.

[traycerb]

Thanks for the great instructable. I had the same dilemma, and some websites mentioned a solution was to build an "interior frame" but I wasn't clear on what that entailed. Your detailed diagrams helped me finish building this yesterday, and I had my first pleasant night in 2 months. I'll be putting up plexi, (got a temporary cover over the top right now), and I still need to weatherstrip the (sizeable) gaps, but all-in-all, it turned out great.

[CANDACE SMALL]

DO YOU LIVE NEAR HAMILTON?
I WOULD GLADLY PAY YOU TO HELP ME INSTALL MINE PERMANENTLY USING THE PLEXIGLASS.
THE WOOD AND OTHER STUFF IS TOO UGLY.
THANKS
CANDACE

[nevroth]

THANK YOU! My boyfriend and I used this guide to make a frame to fit in my windows for an A/C. Super cheap and easy. I had spent $32 on a proper "mounting frame" but it still seemed unsteady so we checked online and found your guide! The 2x4s only cost $6 and it took MAYBE an hour from first cut to last screw drilled in place. The best part is that I can take it with me when I move, and can help friends to make their own. To "pretty it up," I'm going to cover the wood with a painting/drawing of mine. I thought about painting it to match the walls, but it doesn't look bad at all really- and it WORKS!!

[nevroth]

Ack, I just wanted to mention, that to get an angle for any water to drip out, once the sides and bottom were done, I held the A/C with the back tilted downwards a bit, and my boyfriend put the middle bar right on top and drilled it in place (from outside the frame in, of course). So instead of being straight, the middle bar is already at an angle. Also, we drilled the frame into 3 sides of the window sill - that sucker is going NOWHERE! (I mention it because I didn't quite understand your directions, although my boyfriend knew what you were talking about, lol) THANKS again.

[starshipminivan]

The way you screwed in the center bar makes sense. Yeah, I can see that it might need to go in at an angle to keep the unit angled. I'm also glad that you guys figured out how to secure the frame. I'll bet that thing is solid! It makes me very happy that people are getting some use out of these instructions. I have crank windows now and don't have my pics of this project because I didn't even think of documenting it as an instructable when I was making my frames for the old windows. So I have to rely on my words, some drawings, and old pictures. My husband thinks I might have over-engineered the frames a little but I figure safety first!

[bfarm]

This would go well with an upholstered couch on the front porch and lots of external cable TV wires. Some old tires on the front lawn (or blacktop) would complete the look.

[canida]

Hey, be nice!

Few a/c hacks are pretty, but when it's hot you do what you need to do to stay cool.

[starshipminivan]

I can live with it for two months out of the year and I think a lot of other people feel that way too. I've been in beautiful houses that are hot hellholes in the summer. My guests would be more offended if I didn't have air conditioning because my 2nd story gets quite hot without it. Once built, I can install and uninstall it in a few minutes which is its beauty.

[LauraBS]

I think that looks great.
Sure, the Plexiglas looks nicer but I'm sure the cost is high on that.

I have the window brackets to hold my air conditioner in, but don't have a clue how to install properly. No instructions, purchased used.

Is there any way you could show how to do that?

I would really appreciate.

I can't even figure out how to remove the air conditioner from the case to install to the brackets first and then put the conditioner back into the case.

That is what a neighbour said they thought I should do.

I have searched for hours online looking for some kind of instruction with no luck.

Thanks for all your suggestions.
Laura

[starshipminivan]

I'm sorry you had problems with your air conditioner. I see it's been over a month since you posted. I hope you managed to install it and enjoy it.

[LauraBS]

Thanks for your concern. I did get it set in the window, but not exactly the way I was looking to do it. Keeping cool though. :)

[rayterrill]

Excellent work, starshipminivan. I used this Instructable last night, and had my AC unit installed in my casement window in just over 1 hour. Well done! :D

[starshipminivan]

It is so neat that people are actually using these instructions! Stay cool!

[rayterrill]

As soon as I saw how much more expensive the sliding/casement-style AC units were (3-4 times as expensive as the ones intended for double-hung windows!), I thought 'someone has already solved this problem'.

I also mentioned it in my little blog - http://rayvstheworld.com/2010/07/installing-a-standard-ac-unit-in-a-horizontally-slidingopening-window/.

Thanks for the help!

[starshipminivan]

Thanks for the link! That cost issue is precisely why I built these frames. My air conditioners worked just fine, so why buy replacements when you can fit a square peg into a round hole with a little bit of lumber and time? Enjoy your air conditioner.

[iTinkers]

Plexiglas could be a good idea to allow some light.

[starshipminivan]

I see that lots of people are doing this which is great. Since the gap covering piece isn't part of the structure itself, I guess you could put in just about anything.

[HowardC]

It looks good, but a word of warning.... You should really be protecting the outside of the window frame or else it will rot. And yes even if the window is underneath a porch or gutter this should be a concern. I just replaced a window frame because of that. I've done this differently over the years btw. Keep in mind that the A/C is what you are trying to hold up, NOT the plywood. With that being said I generally don't put any sides on the plywood. You screw the plywood to the top bracket on the a/c... screw a 1x4 on each side of the plywood on the frame side, thus wedging both boards tight against the window frame which makes the plywood sturdy enough to hold the weight of the A/C the bottom hooks on the ac are put on the inside of the frame, NOT the middle, thus giving the angle we need for drainage. Pool noodles or somehting similar are put on the window glass side of the plywood and the L-brackets supplied with the ac are used to clamp the window tight against the plywoood. The benefits of this method are the fact that the plywood is inside the window frame, which looks better, and the plywood is only as wide as the a/c, which gives you more window and thus more light.

[starshipminivan]

I do hope you understand this is a temporary installation, despite its sturdiness. It should go in when the warm weather hits and be removed after, which is how most people do their installs. I believe this is the beauty of this projects--that, once built, the a/cs can be installed and removed in minutes once the frame is built. (I have a pet peeve about the tarped-over window air conditioners that I sometimes see in the middle of winter that are not only leaking in cold air but leaving the windows open to the elements.) Common-sense cautionary tales aside, the plywood is NOT the most important part of the install on this frame. Perhaps in the instructable you will likely author for installing an air conditioner, it is, but in the case of mine, it is not. Actually, it is the whole point of this project NOT to lean the air conditioner against the frame of the window or wedge it into the window itself in any way. In my project, the wood frame is crucial in both holding the a/c in place without using the window frame itself, which can be damaged if used in this way, to bear the weight AND in maintaining the proper drainage angle. It is this frame that is screwed into solid wood so the a/c isn't leaning against the window or sitting on the bottom rail of the window, which it can damage. With this framing method, you DO need lumber underneath the unit to allow for this narrow lip to sit against the frame and not on the ledge itself. If you read these instructions, the bottom lip IS inside the frame, not in some "middle" area. The top and bottom lip of the air conditioner itself are installed on the unit in a manner that, when mounted in a double-hung window according to its design, will coordinate so as to create at least the minimum angle necessary for the a/c to drain. So when it it placed in the frame, it will create at least this angle (which is, by the way, 15 degrees). Unlike the plywood-wedge method, my instructable addresses the ability to change the angle at which a particular unit will tip by changing the location of the framing piece that the top lip sits against.

[dlanemarker]

I did the same thing for mine but I used a Plexiglas piece instead of the plywood makes it look a little nicer.

[ikssk]

Good job, I just mounted mine, instead of plywood i used Plexiglas. I will take some pics and post them.

[ikssk]

http://www.flickr.com/photos/13183378@N08/

[Oryctolagus habilis]

Fantastic, both of you! I just moved into the same problem & was thinking plexi!

[ikssk]

Thank you.

[starshipminivan]

Plexi is a great option! I was thinking of painting my board to help protect it and to make it less ugly.