Window A/C Support Bracket Install with Concrete Sill

we recently got a couple of the top shelf ac bracket which does not require any drilling and seem more stable than the other stuff on the market. Its not cheap though, you can get it at Amazon. Its very easy to install and put on, so far its been good for our tenants. Also they have other brands that makes similar design, no drilling brackets.

would you have a photo of that ? I have a similar problem in a 60’s building with slate (i think) sills and no wood to screw into. i was considering improvising some sort of wood support system.

When I installed a heavy AC with a sleeve in a window with aluminum replacement windows with a thin interior lip, I measured carefully and got a piece of wood the length of the AC (something like a 4 x 4, which is what worked with my interior sill) and had a carefully measured chunk cut out of it (something like a quarter of the block of wood.)  Then I was able to set this now L-shaped piece of wood on the inside, just inside the window frame lip, flush against it, with the lower edge of the block of wood resting on the interior brownstone wood window trim just below.  I then took three long screws and screwed through the 4 X 4 into the wood window sill below.  I now had a securely attached flush wood base to screw the sleeve into, as the height of the wood block was the same height, or just slightly higher than, the metal window frame lip.  In my old brownstone, there was sufficient old wood framing around the replacement window to make this possible – it sounds like there may be in your interior as well, if you are thinking about using wood blocks in the interior.  I would just say to securely attach the wood to the interior, if you can, as these big ACs are heavy, and to use 1 block of wood cut to fit, as I did, rather than blocks piled on blocks, as the blocks might be able to shift if piled on one another, making installation difficult.  It was easy to figure out what I needed to make a secure flush surface – I just had to measure and draw what I needed carefully for the place that did the cuts in the wood for me.  When the AC was in place, I also screwed through the lip on the top of the sleeve straight on through the metal edge of the window sash. (The metal sash frame was strong enough, and I owned so had no landlord to worry about.  I was careful not to screw too near the pane, so as not to mess up the seal between the two panes of glass in the double pane window.)  Screwing the sash to the sleeve was important, not only to keep the AC securely in place should the window sash shift, or should some idiot raise the window sash from inside to get air, but also to keep burglars from pushing in the AC or raising the sash above it….a prime way of entering through windows is to push in a not securely attached window AC unit. You will need to be careful about this, as mentioned above, because your vinyl sash may not have the strength to take this.  And if your unit needs to be angled slightly downward to allow water to drip out (mine did not, as the water did not drip out, but was reused to provide additional cooling), then this will put even more stress on the window frame.  Attaching a tube to take off the drip may help you not to have to angle it (read the AC instructions carefully), reducing the stress on the sash caused by angling, as well as having the effect of not having your downstairs neighbor have the plop of your drips on their AC unit or sill. (I have never installed an AC with vinyl windows, so I don’t know how strong they are or how easily they warp.)  I have seen installations where the sash was not drilled, but where the sash was prevented by moving up by wood blocks installed above the sides of lower sash.  I seem to remember seeing an installation where the sash was pushed all the way up, and a clear thick piece of hard plastic was then securely inserted in the space between the AC and the upper sash, and the AC sleeve screwed into this plastic, I think (a professional installation, not done by my friends.)  When in doubt, you can always hire a professional installer – smaller stores that sell ACs definitely provide this service…I think J & R, in Park Slope, on 7th near Union used to do installs for a not so large fee.  Larger stores may as well, I don’t know.  As for the exterior, I didn’t need to use a bracket, just the usual 2 x 4s, resting on the exterior stone sill.  I was able to pile these so the AC sleeve and unit rested securely on them, and with the heavy AC resting on them, angled out ever so slightly downward, they weren’t moving anywhere.  Of course, my sill was wider than a 2 x 4, and extended far enough out that the unit was securely balanced.  My AC was fairly square, and didn’t extend out much past the sill – some of the narrower units, like the ones installed in casement windows, look like they are much longer than they are wide, so depedning on the shape of your unit, and the extension of your exterior sill, yours may not balance securely on your sill without a bracket.  A bracket is a less unsightly look.  I agree that brackets are not designed to be screwed into the concrete or masonry.  You can see how they work by walking around and looking at them, the ones that look like the AC is securely supported, rather than the ones that look like they could come crashing down on pedestrians.  If your exterior window sill is wide enough, the bracket might rest on it, or if not, the bracket will support the AC by resting against the vertical brick wall below the window sill.  Professional installers know how the brackets work best if you can’t figure out how to securely attach it to your satisfaction – and could well be worth the money.  Good luck.  Oh, and having the sleeve only helps slightly with the difficulty of having to position the heavy AC in the window – I had a different brand, but the metal of the sleeve was thin, and the AC so heavy, that I had to be careful not to warp the sleeve when installing the AC inside it.  It is having the exerior supports in place (in my case, 2 x 4s on the sill, in your case, the bracket) that keeps the AC from falling outside as you install it, I always figured, not the sleeve.

Do not drill into your masonry sill (and create a point for water entry).  The bracket will transfer the load of the unit onto the sill or the wall below.  Also, do not use any wood blocks/shims on the outside that aren’t anchored to the building – that’s a DOB violation and (if your building is more than 6 stories) a Local Law 11 violation.  But good for you for trying to do this safely!  The walking public appreciates it!

Definitely put in wood support pieces around that lower lip to take the weight off the vinyl – otherwise you will end up warping or breaking that piece.  Just make sure to get screws long enough to go through the wood and solidly into the sill.  Not sure how you are planning on using that bracket – the sleeve has rails on the bottom on which the actual unit rests, but it’s open at the bottom, no?  If the sleeve brackets reach below the sill (they should) you could attach them to a 2×4 which rests against the building.  The friction should be enough to take a good bit of the load, and will save you from drilling the masonry (which your landlord may not appreciate).  Not technically correct, but works. You may also want to consider cutting a wood or metal strip for the top of the sleeve on the inside which goes from frame to frame across.  The sleeve then rests against that instead of the window sash.  Vinyl windows really suck structurally and those units are heavy.  Last thing you want to do is warp the window so come winter it doesn’t shut properly.