What is the ideal height to install a split AC?

The ideal height for a split AC indoor head

The indoor head of a split AC usually goes high on the wall, with its top about 7 feet off the floor and a gap of several inches below the ceiling so it can draw air in. Each maker's install manual gives the exact clearance for its model, and that manual wins over any rule of thumb.

High placement lets cool air fall across the room in summer. In heating mode the vanes point down to push warm air to the floor.

Why high on the wall

Cool air sinks. A head near the ceiling spreads it across the whole room instead of pooling it by the floor. It also keeps the head out of the way of furniture and people, and the remote's line of sight is clear from anywhere in the room.

The trade-off is winter. Warm air rises, so a high head heating a room can leave the floor cooler. Angle the vanes down and use a higher fan speed when heating, and it evens out.

Other placement rules for the indoor head

Where the outdoor unit goes in a snowy town

In Duluth this is the half people forget. Set the outdoor unit above the snow line, on a raised stand or a wall bracket, so drifts don't bury the coil. It runs defrost cycles in winter and drains water, so it can't sit in a spot where that water refreezes into a block of ice. Keep it out from under the roof's drip line, where falling snow and ice hit it, and leave room on all sides for air.

Line set length and the route through the wall