Biomass Thermal Utilization Act of 2019 or the BTU Act of 2019 This bill expands the tax credit for residential energy efficient property to include 30% of qualified biomass fuel property expenditures for property placed in service before 2024. A qualified biomass fuel property expenditure is an expenditure for property that uses the burning of biomass fuel (a plant-derived fuel available on a renewable or recurring basis) to heat a dwelling used as a residence, or to heat water for use in such dwelling, and which has a thermal efficiency rating of at least 75%. The bill also allows (1) a 15% energy tax credit until 2024 for investment in open-loop biomass heating property, including boilers or furnaces that operate at thermal output efficiencies of at least 65% and provide thermal energy in the form of heat, hot water, or steam for space heating, air conditioning, domestic hot water, or industrial process heat; and (2) a 30% credit until 2024 for investment in such property that operates at a thermal output efficiency of at least 80%.