Which of the following is NOT an indoor unit type used in mini-split systems?

In mini-split systems, the types of indoor units commonly used include wall-mounted units, ceiling cassettes, and floor-mounted units. Wall-mounted units are installed high on a wall and are very popular due to their efficiency and minimal space requirements. Ceiling cassettes are recessed into the ceiling, providing a sleek look and allowing for even air distribution throughout the room. Floor-mounted units are designed to sit against the wall and offer flexibility in installation, particularly in spaces where wall or ceiling mounting isn't practical.

Crawl spaces, on the other hand, are typically used for plumbing and electrical access or for housing mechanical systems, not as a type of indoor unit for climate control. They do not function to deliver conditioned air or provide heating and cooling like the other mentioned unit types. Therefore, identifying crawl spaces as not being an indoor unit in mini-split systems aligns well with understanding the distinct purposes and applications of the various unit types.