The glazed kind, that is.
Last weekend, we took the Caer's sole window air-conditioner out for the winter, having used it only three times all summer, and having found it last winter to be a persistent source of major and hard-to-block cold drafts. In the process, despite taking all feasible care, we cracked the glass in the bottom of the window, because the window was badly bodged together and the air conditioner equally badly bodged into it. (For example, a half-inch gap all the way down one side of the air conditioner turned out to be "sealed" with only a single thin strip of open-cell foam.)