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

Picture of 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.

2X4s *(2 or less but the amount varies)
12 deck screws (or other long wood screws)
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.
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buradd made it!1 year ago

YAY! I have a window AC in my sliding casement window now! Thank you so much for the instructable, very easy to follow! The only thing I had to get differently was a more powerful drill because the cheapo I had wouldn't even go thru the wood without the battery dying. I used 1x1's for the frame with a 2x4 base standing upright (to clear the window frame) It's soooooo coool in my room now! Love it! Thanks again!

starshipminivan (author)  buradd1 year ago

Great job! It looks good. I hope you enjoy your cool sanctuary!

Tinker Tom made it!3 years ago
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.
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starshipminivan (author)  Tinker Tom3 years ago
What a beautiful thing! $45 for such a nice finished product is great! I love the miniblinds and curtains.
Thanks. I have a southern exposure so the blinds and curtains help block the midday sun.
nevroth5 years ago
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 nevroth5 years ago
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 (author)  nevroth5 years ago
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!
MikeS681 month ago

I tried hard to get someone--anyone!--to install a standard a/c unit in a slider window in our living room but no luck. One guy who came over said I needed a mini-split system (not a piddly window unit) and gave me a quote of around $4,000. I wish I could afford that, but that is definitely not in the budget. Which is why this post is a godsend.

I'm about the furthest from a carpenter a guy could possibly be. Still, these instructions looked, well, doable, even for me. Spent about an hour walking around the local big box hardware store looking for lumber and plywood and deck screws. I also had to buy a cordless drill and a cool trim saw attachment I used for the plywood panel. Wife and dog are happy now. Guess that makes me happy too. Mahalo starshipminivan!

alex.melodymaker made it!3 months ago

Took about four weekends + several visits to the hardware store at different phases of the build to make two of these for our apartment, but it was well worth it. Thanks to starshipminivan for this Instructable, and also to Tinker Tom for the pics of his modified version that gave me the idea to take this project a step further.

jackel_III made it!5 months ago

Thanks for the instructions, I added Plexiglas rather than wood. It was fairly easy to make

air conditioner.jpg
Riorank. made it!5 months ago

All done.

yes great instructable, I wish I would have seen this last year.

i am wanting to do this in a pinch. I pulled a table up to window , stacked books, to prop ac up to level of sill. Taped a painting in window and cardboard to fill gaps. But, the water wouldn't drip out window because it was tilted toward the sill , inside. Hence not platform.... Now i have dismantled. Suggested to me to use siding inside of painting which is framed. Does siding come in slabs rather that strips, i wonder. Any suggestions. I'll watch the video in How To steps you provided. I want to see how to sit my ac onto the sill. I dont see a platform here in pic, and that's usually how it's done.

seaweed0094 years ago
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 (author)  seaweed0093 years ago
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-kun4 years ago
How do you screw together the 2x4's when they are perpendicular to each other?
starshipminivan (author)  jenga-kun4 years ago
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.
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 (author)  jenga-kun3 years ago
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.
stubbsonic4 years ago
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.
jsanchez174 years ago
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 (author)  jsanchez174 years ago
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.
debbiedoo4 years ago
Thank you again for the diagram confirming installation. : )
marquisk24 years ago
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 (author)  marquisk24 years ago
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.
traycerb6 years ago
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.
bfarm5 years ago
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 bfarm5 years ago
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 (author)  bfarm5 years ago
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.
LauraBS5 years ago
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.
starshipminivan (author)  LauraBS5 years ago
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.
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. :)
rayterrill5 years ago
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 (author)  rayterrill5 years ago
It is so neat that people are actually using these instructions! Stay cool!
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 (author)  rayterrill5 years ago
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.
iTinkers5 years ago
Plexiglas could be a good idea to allow some light.
starshipminivan (author)  iTinkers5 years ago
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.
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