I bought a portable unit last year and was advised by a friend to buy a window seal kit. It cost about ?13 and is basically some Velcro to stick all the way around the inside of your window frame and then a triangular shaped strip of fabric that sticks to the Velcro, so when you open the window to put the vent tube out, it stops the air from getting out too. It comes with a zip, you open the window, undo the zip and stick the tube through the open zip and out of the window. When you are finished you simply remove the tube and the window closes with the seal still intact. I couldn?t get the link from Amazon, but if you search for air con window seal, you will see what I mean. It took less time to set up than I?ve spent explaining it! Really easy to do and keeps the draft out and the lovely cool air in!