You can.
In principle, very easily, with no harm to the unit, or losses.
In practice, mebbe not so easy.

The only real issues at hand are getting the output cold air into the house,
getting the intake *house* air into the unit, AND keeping them separate.
In principle, you could do this with duct tape and 3 mil garbage bags! Just
make sure the output/input are separated a few inches past the window, so
they don't mix too much--which is a kind of HVAC "air short circuit".

You could also do this with duct tape and 1/8 beaver board. The more
accurate your cuts/angles, the easier your life will be. You will also need
a piece of wood in the window about the same width by height as the unit,
with cutouts for the intake/ouput.

IOW, you are just making two separate ducts, with a common wall.

Having said that, indeed mini-splits are Da Bomb. Most are at least as
efficient as any window unit, some much much more efficient, and much
quieter.
And, I've seen on-line stuff pretty cheap. 9,000 btu units for about $500,
which means you could put in two in your place for much better and more
economical cooling.
--
------
Mr. P.V.'d (formerly Droll Troll), Yonkers, NY

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entropic3.14decay at optonline2.718 dot net; remove pi and e to reply--ie,
all d'numbuhs

"Ray" wrote in message
news:B6Vfi.5243$9b5.860@trndny05...
We live in an L-shaped, five-room apartment with 1600 square feet.
(Exluding hall, kitchen, and 2 baths.)

For several years we have used a 23,000 BTU window air conditioning unit
which cools the entire apartment adequately for our needs.

The only problem is, it makes a lot more noise than we like.

Would it be possible to place the entire unit on the outside, probably on
a platform just below the window, and rig up some customized ducts to
handle the intake and outflow to carry the air into the apartment? This
would involve some sheet-metal fabrication, of course, and I'm sure we
would still hear some noise, but diminished. But the cost would be a great
deal less than central air.

Any ideas welcome.