Mechanical Insulation Installation Incentive Act of 201 9 This bill allows an additional tax deduction for a portion of the cost of installing mechanical insulation property. The bill limits the amount of such deduction to the lesser of (1) 30% of the cost, or (2) the reduction in energy loss from the installed mechanical insulation property compared to property that meets the minimum requirements of American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard 90.1-2007. The bill allows the cost of mechanical insulation property that is placed in service to replace insulation property to be treated as a deductible business expense in the current taxable year. The bill defines "mechanical insulation property" as insulation materials, facings, and accessory products (1) placed in service in connection with a mechanical system which is located in the United States and of a character subject to an allowance for depreciation; and (2) utilized for thermal requirements for mechanical piping and equipment, hot and cold applications, and heating, venting and air conditioning applications which can be used in a variety of facilities. The bill also allows a tax deduction for capital expenditures related to mechanical insulation property.