For my garage I have an electric space heater (5 kw, 220 volt) direct wired to a dedicated 240v/30 amp circuit. I'm upgrading the wiring with for new lights and receptacles and would like to provide for a window air conditioner. With the size of the garage (20 x 24 x 12 ft) I'm right at the upper border of window A/C units that use 120/20a circuits, so I'd like to provide for using a 220 volt unit if necessary. Since the heater and the A/C won't be used at the same time, can I just add a 240v outlet near the window onto the heater circuit, or is that a no-no?