HVAC contractor services; Installation, maintenance and repair of HVAC systems and equipment, plumbing systems, air ducts, indoor air quality systems, ductless mini-split units, furnaces, boilers, water heaters, gas fittings and connectors; Plumbing contractor services; Plumbing services; Air duct cleaning services; Comprehensive preventive maintenance of medical gas systems for others; Extraction of gas; Installation of gas and water pipelines; Installation of apparatus for supply and distribution of gas; Installation, maintenance and repair of apparatus for supplying gas; Laying, repair, maintenance, replacement and refurbishment of gas pipelines; Maintenance and repair services for gas pipelines; Plumbing and gas and water installation; Technical consulting related to the installation of oil and gas equipment, control systems, and machinery