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Installation of central air conditioning, refrigeration, heating and ventilating systems, including ductwork in connection with a complete system only to the extent such ductwork is performed by the contractor as is necessary to make complete an air-distribution system, boiler and unfired pressure vessel systems, and all appurtenances, apparatus or equipment used in connection therewith; installing piping, insulation of pipes, vessels and ducts, pressure and process piping, pneumatic control piping and connection of power wiring; to install a drain from an air conditioning unit to an existing safe waste or other approved disposal other than a direct connection to a sanitary system. Shall not include any work such as liquefied petroleum or natural gas fuel lines within buildings, potable water lines or connections thereto, sanitary sewer lines, swimming pool piping, and filters, or electrical power wiring on the line side of the disconnect switch.