Back-to-back installation

A back-to-back installation mounts the indoor unit on an external wall with the outdoor unit directly behind it, needing only a short pipe run through the wall, the cheapest standard install.

It's the configuration "standard installation" pricing usually assumes, and why quotes climb when your layout can't do it: every extra metre of refrigerant pipe, wall bracket or condensate pump is a legitimate add-on. If your quote seems high, ask what stopped it being back-to-back, the answer tells you whether the premium is real.