This industry comprises establishments primarily engaged in installing and servicing plumbing, heating, and air-conditioning equipment. Contractors in this industry may provide both parts and labor when performing work. The work performed may include new work, additions, alterations, maintenance, and repairs. Illustrative Examples: Cooling tower installation Heating, ventilation, and air-conditioning (HVAC) contractors Duct work (e.g., cooling, dust collection, exhaust, heating, ventilation) installation Lawn sprinkler system installation Fire sprinkler system installation Mechanical contractors Fireplace, natural gas, installation Refrigeration system (e.g., commercial, industrial, scientific) installation Furnace installation Sewer hookup and connection, building Cross-References. Establishments primarily engaged in--