A typical system consists of an outdoor unit (comprising one or multiple compressors), several indoor units (often and mistakenly called "fan coils"), refrigerant piping, running from the outdoor to all indoors, using copper distributors in pipes and communication wiring.

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Outdoor units are light in weight and have a small footprint.  This means that they will fit in a service elevator, so no crane is required for lifting to a rooftop installation.  In some cases, savings on the total construction cost can be achieved since the lightweight unit means that additional support structure in the roof is not required.